Improving Compatibility between Trimethyl Phosphate and Graphite Anodes by Preconstructing a Stable Solid Electrolyte Interphase Film

Abstract

The electrolyte additive of trimethyl phosphate (TMP) shows a good flame-retardant property for lithium-ion batteries (LIBs) comprising nonaqueous carbonate solvents. However, TMP is not conducive to cycle performance because of its poor compatibility with graphite anodes. Herein, a stable solid electrolyte interphase (SEI) film on the graphite surface is preconstructed by cycling the Li||graphite half-cell with the 1.5 M lithium difluoro­(oxalato)­borate (LiDFOB)-ethylene carbonate (EC)/dimethyl carbonate (DMC) electrolyte for five cycles. The as-generated stable SEI film is relatively rich in LiF and lithium oxalate, which helps to restrain the cointercalation of Li+-TMP and improves the compatibility between TMP and the graphite anode. As a result, the modified Li||graphite cell enables a good flame-retardant property and excellent electrochemical performance, even if the 0.7 M LiDFOB-EC/DMC/TMP(40%) electrolyte is used in the subsequent cycles. This study emphasizes the importance of constructing a stable SEI film and provides a reference method for designing safe and practical electrolytes for LIBs.

Building a Flexible and Highly Ionic Conductive Solid Electrolyte Interphase on the Surface of Si@C Anodes by Binary Electrolyte Additives

“…As reported, a stable SEI is established as a prerequisite for realizing the practical application of silicon-based anode cells. − Thus, various types of electrolyte additives which are usually able to preferentially form stable SEI on the anode surface before the decomposition of electrolyte body are used in Si-based LIBs. , It is reported that additives of fluoroethylene carbonate (FEC), vinyl carbonate (VC), (pentafluoro­phenyl)­borane (TPFPB), lithium bis­(oxalate)­borate (LiBOB), and lithium difluorobisoxalate phosphate (LiDFBOP) have shown positive effects on improving the cycle life of Si-based anodes. − FEC has once been considered as the most promising additive because its reduction products are mainly composed of polyolefins and LiF, and its derived SEI has characteristics of flexibility and high ionic conductivity. However, FEC will decompose at high temperature to generate gaseous products, especially HF, which is very destructive to cycling and safety performances .…”

Non-Flammable Electrolyte Mediated by Solvation Chemistry toward High-Voltage Lithium-Ion Batteries

“…This analysis is consistent with the phenomena, which implies that the Li + -TMP would undergo a severe decomposition readily when it was cointercalated into the graphite layers compared to that on the graphite electrode surface, consequently causing the graphite exfoliation as observed before. 48,49 On the cathode side, the PF 6 − -TMP could also be oxidized readily due to the high HOMO level value of PF 6 − -TMP (i.e., −0.191 hartree), particularly at the high-voltage operations (Figure 1b). To optimize the performance, it is essential to attenuate the interaction between Li + and TMP.…”

Breaking Solvation Dominance of Phosphate via Dipole–Dipole Chemistry in Gel Polymer Electrolyte

“…While phosphate-based electrolytes have shown significant success in lithium metal electrodes, their compatibility with graphite anodes remains an underexplored area, necessitating further research to unlock their full potential in high-safety LIBs technology. Researchers have been actively pursuing various methodologies to address this challenge. − For example, Xu et al have proposed a method that preconstructing a stable solid electrolyte interface (SEI) film on the graphite anode’s surface effectively mitigates the adverse effects of phosphates on graphite . However, the long-term cycling performance of this approach is compromised by the irreversible damage to the preprepared SEI .…”

“…18−20 For example, Xu et al have proposed a method that preconstructing a stable solid electrolyte interface (SEI) film on the graphite anode's surface effectively mitigates the adverse effects of phosphates on graphite. 21 However, the long-term cycling performance of this approach is compromised by the irreversible damage to the preprepared SEI. 22 Another proposed solution revolves around electrolyte engineering, which includes strategies such as reducing the concentration of phosphate-based species or increasing lithium salt concentrations in the electrolyte to minimize adverse cointeraction behavior.…”