Low-Temperature Performance Improvement of Graphite Electrode by Allyl Sulfide Additive and Its Film-Forming Mechanism

Abstract

This work describes the beneficial effects given by the allyl sulfide (AS)-derived surface film on the low-temperature performances of graphite electrode and the film-forming mechanism. Adding a small amount of allyl sulfide as an electrolyte additive into a Li/graphite cell increases the reversible capacity of graphite electrode to three times larger than that of the AS-free cell at −30 • C. Lithium plating is also suppressed by adding AS into the background electrolyte. An impedance analysis reveals that the charge transfer resistance is significantly lower in the AS-added cell at low-temperatures. When the graphite electrode is soaked in the AS-added electrolyte, allyl sulfide is spontaneously oxidized to produce the sulfur-containing surface film. The as-generated film is then electrochemically reduced during the first lithiaiton period to produce another type of the sulfur-containing film. After repeated cycling, a carbon-rich sulfur-containing film is generated near the graphite surface, while the decomposition products of background electrolyte are deposited in the outer surface region. The presence of the carbon-rich sulfur-containing film near the graphite surface seems to be responsible for the facilitation of charge transfer reaction at low temperatures.Adequate low-temperature performance is a key requirement of energy storage devices for hybrid electric vehicles (HEVs) and electric vehicles (EVs). Lithium-ion batteries (LIBs) are the most promising candidate for these applications due to their relatively high energy and power density compared with other power sources. However, for these weather-sensitive applications, LIBs must overcome the drastic decrease in reversible capacity at low-temperatures. 1,2 It is reported that, in severe conditions (< −40 • C), a commercial 18650 cells deliver only 5% of its energy density in comparison to its value at 20 • C. 3 Graphite, the preferred negative electrode for LIBs, is well-known for poor electrochemical performance below −20 • C. 4-6 There are many possible causes for this undesirable feature; increased viscosity and reduced Li + conductivity in electrolytes, 7 the enlarged resistance of the passivation layer called solid electrolyte interphase (SEI), 8 the increase of charge transfer resistances (R CT ) at the electrode/electrolyte interface, 6 and the decrease of solid-state Li + diffusion rate. 9 Due to the enlarged R CT for Li intercalation at graphite/electrolyte interfaces and slower Li + diffusion into graphene layers at low temperatures, Li + ions are reduced into Li metal (lithium plating) on graphite surface instead of intercalation, which causes a serious safety concern. Several approaches to improve low-temperature performances of graphite negative electrode have been pursued in recent studies. 4,6,10,11 The formation of SEI film on graphite electrodes is unavoidable because the working voltage of graphite electrodes is beyond the thermodynamic stability window of typical organic electrolytes. The SEI film passivates the graphite surface, the...

Critical Review on Low‐Temperature Li‐Ion/Metal Batteries

“…[124] Holoubek et al [15] designed the electrolyte of 1 m LiPF 6 with a mixture of methyl 3,3,3-trifluoropionate (MTFP)/FEC (9:1 by vol) for ultralowtemperature application of LMBs (Figure 8b). The synergistic effect of MTFP with excellent oxidative stability (≈5.8 V) and Jurng et al [102] 0.5 wt% DMS 1.0 m LiPF 6 EC/EMC (1:2, wt)…”

“…[96][97][98][99][100][101] Allyl sulfide (AS)-added electrolytes were demonstrated to be spontaneously decomposed on the surface of soaked graphite and form a sulfur-containing inner layer SEI, which facilitated the charge-transfer process at low temperatures. [102] Besides, the addition of 2 wt% AS could also suppress Li plating, further enhancing the low-temperature performance of cells. Guo et al [103] reported that the graphite||NCM523 pouch cells with carbonate electrolyte (1 m LiPF 6 EC/EMC, 1:2 by wt) containing 0.5 wt% DMS exhibited superior low-temperature performance, outperforming the commercialized DTD additive (Figure 7a).…”

Electrolyte Design for Lithium Metal Anode‐Based Batteries Toward Extreme Temperature Application

“…[ 12 ] The SEI film has generally been recognized as the most resistive component in the journey of the Li‐ion transportation. [ 13 ] An increased R ct can be observed as the temperature decreased below zero, indicating the sluggish charge transportation on SEI. [ 14 ] The interfacial and bulk impedances rapidly increased with the decrease of temperature.…”

Hierarchical Sulfide‐Rich Modification Layer on SiO/C Anode for Low‐Temperature Li‐Ion Batteries

“…Some sulfite solvents with high dielectric constant and wide temperature range show excellent compatibility with SiO/C anode, which are usually used as additives of electrolytes to promote the formation of SEI and produce sulfide with low impedance. [26][27][28][29][30][31] However, the oxidation of sulfur-containing solvent at higher potential leads to its continuous consumption and limits its further application in full batteries. [32] In addition, the structure and performance-dependent properties of SEI layer has not been clearly demonstrated which also impede its rational design and optimization.…”