30
H. Kaur et al.
The construction of SEI upon contact with the electrode consists of reduction products of electrolyte (residues) involved during various cycles of lithiation/de-lithiation
[92, 93]. The molecular insight of adsorbed moieties at the SEI requires interfacial
spectrometer techniques that can distinguish in determining the involved role of electrolytes, electrodes and ions in the electrochemical processes [92, 93]. ATR-FTIR
technique offers such substantiality in experiments to study the interactions of the
chosen molecules and solid surface under a wide range of conditions [16, 24, 94–98].
Shi et al. [96] investigated the Li-ion electrolyte reduction process at two different
metal electrodes surfaces (Au and Sn) by in-situ ATR-FTIR spectroscopy. The electrochemical cell used in the study consists of Au and Sn foil as a working electrode
and lithium foil as both the counter and reference electrode. The electrolyte composition of lithium hexafluorophosphate (LiPF 6 ) and ionic liquid of ethylene carbonate
(EC) and diethyl carbonate (DEC) in a proportion of 1 M LiPF 6 /EC: DEC (=1:2 v/v)
were used to elucidate the involved surface chemistry of the reduction process with
a different metal electrode. The working electrode was pressed against a 45°-cut Ge
prism. Assembly of all the three electrodes and electrolytes were kept in a Teflon electrochemical cell. The ATR-FTIR measurements were acquired after providing electrode potential in the range from the open-circuit voltage (OCP) to various potential
values before Li-deposition for 2 h. The in-situ studies showed different pathway reaction of electrolyte in contact with used metal electrodes. Authors identified (Fig. 17,
panel a, b and c) insoluble lithium ethylene dicarbonate (LiEDC) forms on the Au
electrode with the appearance of 1115 cm
−1 at ~0.6 V whereas relatively soluble
dioahexane dicarboxylate (DEDOHC) appears on the Sn electrode (dominant peak
centered at 1744 cm
−1 ) at ~1.25 V with common lithium propionate (characteristic
peak positions observed at 2920, 2851, and 1565 cm
–1 ) formed on both the electrodes. Based on the FTIR observations, it is concluded that two different reaction
mechanisms i.e., a non-catalytic reaction path (Au electrode) and a catalytic reduction path (Sn electrode), to clarify the observed surface dependence. The study shows
important implications in understanding the surface modification dependence upon
the selection of polymer binder, electrolyte and electrode in the SEI formation in the
LIBs.
Shi et al. [16] studied on the electrode/electrolyte interface and focused on investigating the decomposition process of SEI on the graphite electrode during the electrochemical cycling procedure. The work is performed by using in-situ ATR-FTIR
spectroscopy with varying penetration depth. The electrochemical cell utilized for
this study consisted of a silicon working electrode, lithium electrode as both the
counter and reference electrode and an electrolyte. The electrolyte composition of
1 M LiPF 6 (EC: DEC = 1:2 v/v) was used and the detailed description of the cell
is mentioned in their study [16]. The angle of incidence of the IR beam varied from
45° to 65° with respect to the ATR prism. The penetration depth of the evanescent wave decreased on increasing the incidence angle of IR on the sample (refer
Eq. 16), which provided subtle information up to 65 nm depth at ~65
◦ covering the
SEI deposited on the electrode/electrolyte interface. In contrast, the diffuse layer
(∼0.5 μm) at ~45
◦ probed the electrolyte reactivity processes in the bulk phase.
H. Kaur et al.
The construction of SEI upon contact with the electrode consists of reduction products of electrolyte (residues) involved during various cycles of lithiation/de-lithiation
[92, 93]. The molecular insight of adsorbed moieties at the SEI requires interfacial
spectrometer techniques that can distinguish in determining the involved role of electrolytes, electrodes and ions in the electrochemical processes [92, 93]. ATR-FTIR
technique offers such substantiality in experiments to study the interactions of the
chosen molecules and solid surface under a wide range of conditions [16, 24, 94–98].
Shi et al. [96] investigated the Li-ion electrolyte reduction process at two different
metal electrodes surfaces (Au and Sn) by in-situ ATR-FTIR spectroscopy. The electrochemical cell used in the study consists of Au and Sn foil as a working electrode
and lithium foil as both the counter and reference electrode. The electrolyte composition of lithium hexafluorophosphate (LiPF 6 ) and ionic liquid of ethylene carbonate
(EC) and diethyl carbonate (DEC) in a proportion of 1 M LiPF 6 /EC: DEC (=1:2 v/v)
were used to elucidate the involved surface chemistry of the reduction process with
a different metal electrode. The working electrode was pressed against a 45°-cut Ge
prism. Assembly of all the three electrodes and electrolytes were kept in a Teflon electrochemical cell. The ATR-FTIR measurements were acquired after providing electrode potential in the range from the open-circuit voltage (OCP) to various potential
values before Li-deposition for 2 h. The in-situ studies showed different pathway reaction of electrolyte in contact with used metal electrodes. Authors identified (Fig. 17,
panel a, b and c) insoluble lithium ethylene dicarbonate (LiEDC) forms on the Au
electrode with the appearance of 1115 cm
−1 at ~0.6 V whereas relatively soluble
dioahexane dicarboxylate (DEDOHC) appears on the Sn electrode (dominant peak
centered at 1744 cm
−1 ) at ~1.25 V with common lithium propionate (characteristic
peak positions observed at 2920, 2851, and 1565 cm
–1 ) formed on both the electrodes. Based on the FTIR observations, it is concluded that two different reaction
mechanisms i.e., a non-catalytic reaction path (Au electrode) and a catalytic reduction path (Sn electrode), to clarify the observed surface dependence. The study shows
important implications in understanding the surface modification dependence upon
the selection of polymer binder, electrolyte and electrode in the SEI formation in the
LIBs.
Shi et al. [16] studied on the electrode/electrolyte interface and focused on investigating the decomposition process of SEI on the graphite electrode during the electrochemical cycling procedure. The work is performed by using in-situ ATR-FTIR
spectroscopy with varying penetration depth. The electrochemical cell utilized for
this study consisted of a silicon working electrode, lithium electrode as both the
counter and reference electrode and an electrolyte. The electrolyte composition of
1 M LiPF 6 (EC: DEC = 1:2 v/v) was used and the detailed description of the cell
is mentioned in their study [16]. The angle of incidence of the IR beam varied from
45° to 65° with respect to the ATR prism. The penetration depth of the evanescent wave decreased on increasing the incidence angle of IR on the sample (refer
Eq. 16), which provided subtle information up to 65 nm depth at ~65
◦ covering the
SEI deposited on the electrode/electrolyte interface. In contrast, the diffuse layer
(∼0.5 μm) at ~45
◦ probed the electrolyte reactivity processes in the bulk phase.