Prelithiation is of great interest to Li‐ion battery manufacturers as a strategy for compensating for the loss of active Li during initial cycling of a battery, which would otherwise degrade its available energy density. Solution‐based chemical prelithiation using a reductive chemical promises unparalleled reaction homogeneity and simplicity. However, the chemicals applied so far cannot dope active Li in Si‐based high‐capacity anodes but merely form solid–electrolyte interphases, leading to only partial mitigation of the cycle irreversibility. Herein, we show that a molecularly engineered Li–arene complex with a sufficiently low redox potential drives active Li accommodation in Si‐based anodes to provide an ideal Li content in a full cell. Fine control over the prelithiation degree and spatial uniformity of active Li throughout the electrodes are achieved by managing time and temperature during immersion, promising both fidelity and low cost of the process for large‐scale integration.

Although often overlooked in anode research, the anode’s initial Coulombic efficiency (ICE) is a crucial factor dictating the energy density of a practical Li-ion battery. For next-generation anodes, a blend of graphite and Si/SiO x represents the most practical way to balance capacity and cycle life, but its low ICE limits its commercial viability. Here, we develop a chemical prelithiation method to maximize the ICE of the blend anodes using a reductive Li–arene complex solution of regulated solvation power, which enables a full cell to exhibit a near-ideal energy density. To prevent structural degradation of the blend during prelithiation, we investigate a solvation rule to direct the Li+ intercalation mechanism. Combined spectroscopy and density functional theory calculations reveal that in weakly solvating solutions, where the Li+–anion interaction is enhanced, free solvated-ion formation is inhibited during Li+ desolvation, thereby mitigating solvated-ion intercalation into graphite and allowing stable prelithiation of the blend. Given the ideal ICE of the prelithiated blend anode, a full cell exhibits an energy density of 506 Wh kg–1 (98.6% of the ideal value), with a capacity retention after 250 cycles of 87.3%. This work highlights the promise of adopting chemical prelithiation for high-capacity anodes to achieve practical high-energy batteries.

We report the stereospecific ring-opening metathesis polymerization (ROMP) of endodicyclopentadiene (DCPD) by various well-defined molybdenum-based and tungsten-based alkylidene initiators. Tungsten MAP (MonoAryloxide Pyrrolide) initiators with the general formula W(X)(CHCMe 2 Ph)(Me 2 Pyr)(OAr) (X = arylimido, alkylimido, or oxo; Me 2 Pyr = 2,5dimethylpyrrolide; OAr = an aryloxide) yield cis,syndiotactic-poly(DCPD), while biphenolate alkylidene complexes with the general formula M(NR)(CHCMe 2 Ph)(biphen) (M = Mo or W; R = alkyl or aryl, biphen = (e.g.) 3,3′-(t-Bu) 2 -5,5′-6,6′-(CH 3 ) 4 -1,1′-biphenyl-2,2′-diolate) yield cis,isotactic-poly(DCPD). Subtle changes in the initiator can greatly alter the structure of the poly(DCPD)s that are formed. Cis,syndiotactic or cis,isotactic poly(DCPD)s (made with 50-1000 equiv of DCPD) are accessible within seconds to minutes in dichloromethane at room temperature. No isomerization or cross-linking reactions are observed, and addition of a chain transfer reagent (1-hexene) or the use of THF as a solvent does not decrease the stereospecificity of the polymerizations. Cis,syndiotactic and cis,isotactic poly(DCPD)s can be distinguished readily from each other by 13 C NMR spectroscopy. Hydrogenation of each stereoregular poly(DCPD) produces crystalline H-poly(DCPD)s that have melting points between 270 and 290 °C.

Ring-opening metathesis polymerization of a series of 3-substituted cyclooctenes (3-MeCOE, 3-HexCOE, and 3-PhCOE) initiated by various Mo and W MAP complexes leads to cis,HTpoly(3-RCOE) polymers. The apparent rate of polymerization of 3-HexCOE by W(N-t-Bu)(CHt-Bu)(Pyr)(OHMT) (1c) (Pyr = pyrrolide; OHMT = O-2,6-Mesityl 2 C 6 H 3) is greater than the rate of polymerization by Mo(N-t-Bu)(CH-t-Bu)(Pyr)(OHMT) (1b), but both gave the same cis,HT polymer structures. Formation of HT-poly(3-RCOE) employing 1c takes place via propagating species in which the R group (methyl, hexyl, or phenyl) is on C2 of the propagating alkylidene chain, a type of intermediate that has been modeled through the preparation of W(N-t-Bu)(CHCHMeEt)(Pyr)(OHMT). The rate of ROMP is exceedingly sensitive to steric factors, e.g., W(N-t-Bu)(CH-t-Bu)(Me 2 Pyr)(OHMT), the dimethylpyrrolide analog of 1c, essentially did not polymerize 3-HexCOE at 22 °C. Upon cooling a sample of W(N-t-Bu)(CHCHMeEt)(Pyr)(OHMT) and 3-methyl-1-pentene in CDCl 3 to-20 °C the alkylidene resonances for W(N-t-Bu)(CHCHMeEt)(Pyr)(OHMT) disappear and resonances that can be ascribed to protons in a syn α /syn α' disubstituted TBP metallacyclobutane complex appear. 3-Methyl-1-pentene is readily lost from this metallacycle on the NMR time scale at RT.

Blue carbon on the rise: challenges and opportunities

Routes to new tungsten alkylidene complexes that contain t-butylimido or adamantylimido ligands have been devised that begin with a reaction between WCl6 and four equivalents of HNR(TMS) to give [W(NR)2Cl(-Cl)(RNH2)]2 (R = t-Bu or 1-adamantyl). Alkylation leads to W(NR)2(CH2R')2 (R' = t-Bu or CMe2Ph) which upon treatment with pyridinium chloride yields W(NR)(CHR')Cl2py2 complexes, from which W(NR)(CHR')(Pyrrolide)2 and two W(NR)(CHR')(Pyrrolide)(OAr) complexes (OAr = hexamethyl-or hexaisopropylterphenoxide) have been prepared. Science Foundation (CHE-1111133 to R.R.S.) for financial support. The X-ray diffractometer was purchased with the help of funding from the National Science Foundation (NSF) under Grant Number CHE-0946721. We thank Professor Kit Cummins for the suggestion that hydrogen bonding is present in 1a.Supporting Information Available. Experimental details for the synthesis of all compounds and details of the X-ray structural studies. Supporting Information is available free of charge via the Internet at http://pubs.acs.org. S2 Experimental SectionGeneral. All air and moisture sensitive materials were manipulated under a nitrogen atmosphere in a Vacuum Atmospheres glovebox or on a dual-manifold Schlenk line. All glassware, including NMR tubes, was oven-dried prior to use. Diethyl ether, pentane, toluene, dichloromethane, 1,2-dimethoxyethane, and benzene were degassed and passed through activated alumina columns and stored over 4 Å Linde-type molecular sieves prior to use. Deuterated solvents were dried over 4 Å Linde-type molecular sieves prior to use. 1 H and 13 C NMR spectra were acquired at room temperature using Varian 300MHz or 500MHz spectrometers. Chemical shifts for 1 H and 13 C spectra are reported as parts per million relative to tetramethylsilane and referenced to the residual 1 H/ 13 C resonances of the deuterated solvent ( 1 H () : benzene 7.16, chloroform 7.26, methylene chloride 5.32; 13 C () : benzene 128.06, chloroform 77.16, methylene chloride 53.84). N-t-butyltrimethylsilylamine was either prepared from TMSCl and t-BuNHLi in ether or purchased from Sigma-Aldrich. The synthesis of N-trimethylsilyl(1-adamantyl)amine has been reported previously; i our preparation employed the n-butyllithium and chlorotrimethylsilane. Pyridinium chloride was purchased from Sigma-Aldrich or Alfa Aesar and sublimed before use. Ethereal solutions of HCl were prepared by bubbling HCl gas into diethyl ether; these solutions were titrated before use. Neopentyl Grignard ii , HMTOH iii , HIPTOH iv , and ZnCl 2 (dioxane) v were prepared according to literature procedures. All other reagents were used as received.[W(N-t-Bu) 2 Cl(μ-Cl)(t-BuNH 2 )] 2 (1a).The following procedure was adapted from a recent publication. vi A solution of N-t-butyltrimethylsilylamine (25 g, 172 mmol) in 30 mL toluene was added slowly over a period of 50 min to WCl 6 (15.2 g, 38.33 mmol) in 150 mL of toluene. The reaction mixture was stirred for 24 h at room temperature. The dark green mixture was filtered through a pad of Celite, a...

A molecularly engineered lithium–arene complex (LAC) with a sufficiently low redox potential enables the incorporation of active Li in Si‐based anodes to generate ideal Li contents in a full cell. In their Research Article on page 14473, J. Hong, M. Lee, and co‐workers demonstrate how the prelithiation degree and the spatial distribution of active Li in the electrodes can be precisely controlled by using the tailored LAC solution.

Ring-opening metathesis polymerization (ROMP) of methyl-N-(1-phenylethyl)-2azabicyclo[2.2.1]hept-5-ene-3-carboxylate (PhEtNNBE; (S) and racemic) was investigated employing six molybdenum and tungsten imido alkylidene initiators and two tungsten oxo alkylidene initiators. Of the six initiators that we proposed should yield cis,syndiotacticpoly[(S)-PhEtNNBE], two molybdenum OHMT alkylidene initiators, Mo(NR)(CHMe 2 Ph)(pyr)(OHMT) (R = Ad or 2,6-Me 2 C 6 H 3 ; OHMT = O-2,6-Mesityl 2 C 6 H 3 ; pyr = pyrrolide) and two tungsten oxo alkylidene initiators, W(O)(CHMe 2 Ph)(2,5dimethylpyrrolide)(PMe 2 Ph)(OR) (OR = OHMT or (R)-OBr 2 Bitet where (R)-Br 2 BitetOH = (R)-3,3'-Dibromo-2'-(tert-butyldimethylsilyloxy)-5,5',6,6',7,7',8,8'-octahydro-1,1'-binaphthyl-2-ol) produced essentially pure cis,syndiotactic-poly[(S)-PhEtNNBE]. Essentially pure cis,isotacticpoly[(S)-PhEtNNBE] was formed when (S)-PhEtNNBE was polymerized by Mo(NAr')(CHCMe 2 Ph)(OBiphen CF3)(thf) or W(NAr')(CHCMe 2 Ph)((S)-OBiphen Me) (OBiphen CF3 = 3,3'-di-tert-butyl-5,5'-bistrifluoromethyl-6,6'-dimethyl-1,1'-biphenyl-2,2'-diolate; (S)-OBiphen Me = 3,3'-di-tert-butyl-5,5',6,6'-tetramethyl-1,1'-biphenyl-2,2'-diolate). The best initiator for ROMP of rac-PhEtNNBE was Mo(NAd)(CHMe 2 Ph)(pyr)(OHMT) at 0 °C, which led to a polymer that is biased (~80%) toward a cis,syndiotactic structure and that contains alternating enantiomers in the chain (cis,syndio,alt-poly[(rac)-PhEtNNBE]).