The DFT-ReaxFF Hybrid Reactive Dynamics Method with Application to the Reductive Decomposition Reaction of the TFSI and DOL Electrolyte at a Lithium–Metal Anode Surface

Abstract

The high energy density and suitable operating voltage make rechargeable lithium ion batteries (LIBs) promising candidates to replace such conventional energy storage devices as nonrechargeable batteries. However, the large-scale commercialization of LIBs is impeded significantly by the degradation of the electrolyte, which reacts with the highly reactive lithium metal anode. Future improvement of the battery performance requires a knowledge of the reaction mechanism that is responsible for the degradation and formation of the solid-electrolyte interphase (SEI). In this work, we develop a hybrid computational scheme, Hybrid ab initio molecular dynamics combined with reactive force fields, denoted HAIR, to accelerate Quantum Mechanics-based reaction dynamics (QM-MD or AIMD, for ab initio RD) simulations. The HAIR scheme extends the time scale accessible to AIMD by a factor of 10 times through interspersing reactive force field (ReaxFF) simulations between the AIMD parts. This enables simulations of the initial chemical reactions of SEI formation, which may take 1 ns, far too long for AIMD. We apply the HAIR method to the bis­(trifluoromethanesulfonyl)­imide (TFSI) electrolyte in 1,3-dioxolane (DOL) solvent at the Li metal electrode, demonstrating that HAIR reproduces the initial reactions of the electrolyte (decomposition of TFSI) previously observed in AIMD simulation while also capturing solvent reactions (DOL) that initiate by ring-opening to form such stable products as CO, CH2O, and C2H4, as observed experimentally. These results demonstrate that the HAIR scheme can significantly increase the time scale for reactive MD simulations while retaining the accuracy of AIMD simulations. This enables a full atomistic description of the formation and evolution of SEI.

Formation of Linear Oligomers in Solid Electrolyte Interphase via Two‐Electron Reduction of Ethylene Carbonate

“…[35] Unfortunately, the current functional forms of ReaxFF do not include a proper description for explicit electron, which has trouble exploring electron (e -) transfer reaction during electrochemical processes. [36] Islam and van Duin [37] extend the eReaxFF method to treat electrons explicitly in a pseudo-classical manner, and the major reduction reaction pathways were observed, including electron transfer. These theoretical results suggest the initial reduction process of EC, while long-time simulations for SEI formation are still worthy of being clarified.…”

A strong Lewis acid imparts high ionic conductivity and interfacial stability to polymer composite electrolytes towards all-solid-state Li-metal batteries

“…Furthermore, in comparison with the pure PEO/LiTFSI electrolyte, the cycled composite electrolyte exhibited an increased generation of LiF on the surface. LiF was recognized for its ability to inhibit dendrite growth and its existence had been widely verified to stabilize the Li/electrolyte interface [45][46][47]. As all the LiF generated in the subsequent cycling process comes from the decomposition of the TFSI − , it can be inferred that more fresh interfaces had been generated in the pure PEO electrolytes.…”

In situ formation of circular and branched oligomers in a localized high concentration electrolyte at the lithium-metal solid electrolyte interphase: a hybrid ab initio and reactive molecular dynamics study

“…This paper uses a hybrid method, a hybrid ab initio and reactive force eld dynamics (HAIR), to extend the simulation to nanoseconds. HAIR can extend the AIMD simulation to 10 to 100 times while maintaining DFT accuracy, [35][36][37][38] because reactive force eld (ReaxFF) 39 can replace the costly AIMD simulation in accelerating mass transfer when the accuracy or ReaxFF can be trained to level up with AIMD. The details of the simulation setup and HAIR method are as follows.…”