A1722
Journal of The Electrochemical Society, 164 (7) A1720-A1725 (2017)
(ii) Preparation of 4,4ꢀ-bis(methyloxycarbonyl)benzil (3): To the
solution of 2 (740 mg, 2.25 mmol) in dimethyl sulfoxide (10 mL), 3
mL of 48% hydrobromic acid was added under stirring. The reaction
mixture was stirred at 55◦C for 24 h followed by adding 20 mL
deionized water. The obtained yellow colored precipitate was washed
with water and dried at 70◦C overnight (Yield of 3: 710 mg, 96.5%).
1H NMR (400 MHz, CDCl3): δ 8.06 (d, 4H, 8.4 Hz, ArH), δ 7.93
(d, 4H, 8.4 Hz, ArH), δ 3.85 (s, 6H, -OCH3). 13C NMR (CDCl3,
400 MHz): δ 192.86 (-C=O), δ 165.81 (-COOH), δ 135.76 (Ar-C),
δ 135.55(Ar-C), δ 130.16(Ar-C), δ 129.86 (Ar- C), δ52.65 (-OCH3).
(iii) Preparation of 4,4ꢀ-bis(hydroxycarbonyl)benzil (4): 10 mL of
4:1 (v/v) H2SO4/H2O solution was added to the solution of 3 (300 mg,
0.92 mmol) in acetic acid (25 mL). The reaction mixture was refluxed
and stirred for 10 h. Then 20 mL of deionized water was added and
cooled in ice bath. The obtained pale yellow colored precipitate was
washed with water and dried at 70◦C overnight (Yield of 4: 270 mg,
93.7%). 1H NMR (500 MHz, DMSO-d6): δ 8.13 (d, 4H, 8.5 Hz,
ArH), δ 8.06 (d, 4H, 8.5 Hz, ArH). 13C NMR (500 MHz, DMSO-
d6): δ 193.85 (-C=O), δ 166.78 (-COOH), δ 136.91(Ar-C), δ 135.50
(Ar-C), δ 130.56 (Ar-C), δ 130.52 (Ar- C).
(iv) Preparation of 4,4ꢀ-bis(lithiooxycarbonyl)benzil (5): 32 mg of
LiOH.H2O was added to the mixture of 4 (100 mg, 0.33 mmol) and 15
mL of absolute ethanol. The reaction mixture was stirred at 60◦C for
24 h. The obtained pale yellow color solution was concentrated under
reduced pressure and washed with acetone several times to obtain a
light yellow colored solid, which was dried in vacuum oven at 100◦C
Figure 2. HRSEM images of the Li2-BPDC (a, b) and Li2-BZL(c, d) at dif-
ferent magnifications.
1
overnight (Yield of 5: 95 mg, 91.3%). H NMR (500 MHz, D2O):
δ 8.02 (d, 4H, 8 Hz, ArH), δ 7.94 (d, 4H, 8 Hz, ArH). 13C NMR (500
MHz, D2O): δ 196.14 (-C=O), δ 174.23 (-COOLi), δ 143.31(Ar-C),
δ 133.45 (Ar-C), δ 130.20 (Ar-C), δ 129.23 (Ar-C).
bandgap in comparison to that of Li2-BPDC and the intermediate Li4-
BZL formed upon lithiation of Li2-BZL facilitate further lithiation
process, density functional theory (DFT) calculations were carried out
at B3LYP/6-31G (d) level using Gaussian 09 program. The lowest-
unoccupied molecular orbital (LUMO) energy of the Li2-BZL (−2.27
eV) is lower than that of Li2-BPDC (−1.25 eV) (Fig. 3), indicating
easy electronic reduction of Li2-BZL in comparison to that of Li2-
BPDC. The lower bandgap of Li2-BZL (4.01 eV) versus Li2-BPDC
(4.68 eV), indicates higher electronic conductivity of the former. In
addition, bandgap (2.06 eV) of the intermediate Li4-BZL is further
decreased, which enables further lithiation of the carbonyl group of
the carboxylate in Li4-BZL into Li6-BZL.
Material characterization and electrochemical measurements.—
1H and 13C NMR spectra were recorded at Bruker AVANCE 500
MHz spectrometer. The morphologies of the compounds Li2-BPDC
and Li2-BZL were analyzed by a high resolution scanning electron
microscope (HRSEM) FEI Quanta FEG 200. The working electrodes
were prepared by coating slurry on copper foil. The slurry was ob-
tained by mixing of 55 wt% of active material, 35 wt% of acetylene
black (AB) and 10 wt% of polyvinylidene fluoride (PVDF) in N-
methyl-2-pyrrolidone (NMP). The loading of the active materials in
the electrodes is ∼2 mg cm−2. Swagelok cells were fabricated in ar-
gon filled glove box. Cells were galvanostatically cycled by using an
Arbin BT-2000, galvanostat. The specific capacities were calculated
by taking the active materials weight alone. Cyclic voltammetry (CV)
were done using Biologic science instruments VSP model. The sam-
ple preparation for ex-situ 13C NMR experimental procedure is as
follows: two Swagelok cells were assembled with electrodes contain-
Electrochemical lithiation/delithiation performance of samples
(Li2-BPDC and Li2-BZL) were investigated by using two electrode
Swagelok cells. Lithium metal disc served as both reference and
counter electrode and a borosilicate glass fiber sheet separator soaked
ing ∼3 mg of Li2-BZL and cycled at a current density 50 mA g−1
.
These cells were dismantled in the argon filled glove box after the
first charge. The electrodes were cleaned and soaked in the dimethyl
carbonate solvent for 24 h in order to remove the residual electrolyte
from the electrode surface. Next, the dried electrodes were transferred
to a vial containing 1 mL of D2O solvent and subjected to sonication
to extract the active material into D2O, and then the vials were al-
lowed to stand for 24 h. The supernatant solution was collected with a
micro syringe to carry out 13C NMR analysis. The optimized geome-
tries and electronic properties (HOMO, LUMO and Eg) of Li2-BPDC
and Li2-BZL, Li4-BZL were computed by using Kohn-Sham density
functional theory (DFT) in Gaussian 09 suite.
Results and Discussion
Both 1H and 13C NMR spectra (ESI, Fig. S1-S6) reveal the success-
ful synthesis and purity of the Li2-BPDC and Li2-BZL materials. The
morphologies of both Li2-BPDC and Li2-BZL samples were shown
in Fig. 2. The SEM images of the Li2-BPDC and Li2-BZL reveal the
formation of agglomerated micron sized pillar like particles. To ver-
ify our assumption that two carbonyl groups (chromophoric groups)
in the Li2-BZL enhances the electronic conductivity by lowering the
Figure 3. Energy level diagram and frontier orbitals of Li2-BPDC, Li2-BZL
and Li4-BZL generated from Gaussian 09 at B3LYP/ 6-31G (d) level.
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