Improving Toleration of Volume Expansion of Silicon-Based Anode by Constructing a Flexible Solid-Electrolyte Interface Film via Lithium Difluoro(bisoxalato) Phosphate Electrolyte Additive

Abstract

The silicon (Si) anode is considered one of the most promising candidates among many novel anode materials in lithium-ion batteries owing to its high theoretical capacity and earth abundancy. Nonetheless, a large volume expansion of Si particles appears with cycling, prompting unceasing breakage/reformation of the solid-electrolyte interface (SEI) and fast capacity degradation in traditional electrolytes. For the purpose of tolerating volume expansion for the Si anode, lithium difluoro­(bisoxalato) phosphate (LiDFBOP) was adopted in the standard (STD) electrolyte based on LiPF6. Density functional theory (DFT) calculations, Young’s modulus from atomic force microscopy, potential-resolved in situ electrochemical impedance spectroscopy (PRI-EIS) measurement, and other characterizations proved that the formed SEI can inhibit volume expansion of a Si@Graphite@C anode. In the STD+2% LiDFBOP electrolyte, the solvation structure of Li­(EC)2(PF6)1(DFBOP)1 is more likely to be produced, and this kind of solvation structure has stronger reducibility and easily participates in SEI formation. The 2% LiDFBOP additive increases the inorganic LiF component of SEI, which yields great advantages in regulating the uniform diffusion of Li+ ions passing through the SEI. Besides, the organics containing P and F atoms are also abundant in SEI, which has greater flexibility and can tolerate volume expansion of the Si@Graphite@C anode. Therefore, the STD+2% LiDFBOP electrolyte can improve the electrochemical performances of Si@Graphite@C/Li half-cells. This work has practical implications not only for the molecular design of novel lithium salt but also for the constructions of SEI and electrolyte systems compatible with the Si@Graphite@C anode.

Liquid electrolyte chemistries for solid electrolyte interphase construction on silicon and lithium-metal anodes

“…122 Lithium diuoro(bisoxalato) phosphate (LiDFBOP) forms spatially exible SEIs that comprise LiF and phosphorus-/ uorine-containing organics and can tolerate the volume changes due to silicon lithiation and delithiation. 122,123 The building blocks of phosphorus-and uorine-rich SEIs can be formed by the (electro)chemical decomposition of phosphorusand uorine-donating compounds. LiDFP, 120 LiDFBOP, and ethoxy(pentauoro)cyclotriphosphazene (EFPN) were reported to dictate the distribution of phosphorus in the SEI.…”

Basic guidelines of first-principles calculations for suitable selection of electrochemical Li storage materials: a review

“…The substantial volume expansion of Si particles, which leads to constant breakage/reformation of the SEI layer, leads to electrolyte consumption. Wang et al 148 speculated that the volume of Si@graphite@C anode growth could be inhibited by the formation of a stable SEI by adding Li difluoro (bisoxalato) phosphate (LiDFBOP) to a LiPF 6 -based electrolyte. They determined the most likely solvent structure across a variety of electrolytes by calculating the single point energies (SPEs) of various solvation structures.…”

Exploring the Potential of Carbonized Nano-Si within G@C@Si Anodes for Lithium-Ion Rechargeable Batteries

“…These factors contribute to a decline in cycling stability and overall battery performance. 2) Unstable solid electrolyte interface (SEI) formation: The recurrent volume expansion/contraction across charge–discharge cycles cause the SEI layer on the Si anode surface to break and reform repeatedly . This dynamic process results in increased side reactions, lithium-ion consumption, and a decline in Coulombic efficiency.…”

“…2) Unstable solid electrolyte interface (SEI) formation: The recurrent volume expansion/contraction across charge−discharge cycles cause the SEI layer on the Si anode surface to break and reform repeatedly. 9 This dynamic process results in increased side reactions, lithium-ion consumption, and a decline in Coulombic efficiency. 3) Low intrinsic electronic conductivity: Si exhibits poor electronic conductivity (∼10 −3 S cm −1 ), 10 which hampers the efficient transfer of electrons within the anode.…”