Effects of Difluoro(oxalato)borate-Based Ionic Liquid as Electrolyte Additive for Li-Ion Batteries

Abstract

In this work, the use of N-methyl-N-propylpiperidinium difluoro(oxalato)borate Pip13DFOB ionic liquid (IL), originally synthesized in our laboratory, as an additive for liquid electrolytes in lithium-ion batteries (LIBs), is proposed. The synthesized IL exhibits glass and melting transitions at −70.9 °C and 17.1 °C, respectively, and a thermal decomposition temperature over 230 °C. A mixture based on 1.0 M LiPF6 in 1:1 v/v ethylene carbonate (EC): dimethyl carbonate (DMC) electrolyte solution (so called LP30) and the IL was prepared and tested in lithium metal cells versus two different commercially available carbonaceous electrodes, i.e., graphite (KS6) and graphene (GnP), and versus a high voltage LiNi0.5Mn1.5O4 (LNMO) cathode. A noticeable improvement was observed for Li|LNMO cells with an IL-added electrolyte, which exhibited a high specific capacity above 120 mAh g−1 with a Coulombic efficiency above 93% throughout 200 cycles, while the efficiency fell below 80% after 80 cycles with the absence of IL. The results confirm that the IL is promising additive for the electrolyte, especially for a longer cycle life of high-voltage cells.

Ionic Liquids as Cathode Additives for High Voltage Lithium Batteries

“…Regarding PIP 1,3 DFOB, both the glass transition and melting points were observed in the first scan at −67.4 °C and 14.5 °C, respectively. A cold‐crystallization was observed before the melting point, which is a common phenomenon for ILs [6] …”

“…A cold-crystallization was observed before the melting point, which is a common phenomenon for ILs. [6] TGA highlighted the notable thermal stability of both ILs, making their use suitable for battery applications. More specifically, PIP 1,3 BOB has a single decomposition process at 283.9 °C while PIP 1,3 DFOB decomposes through a two-step process.…”

“…The formation of a stable cathode electrolyte interface (CEI) has been recognized as a promising strategy to improve the capacity retention of LNMO [1,5–8] . In this manner, a direct contact between the electrolyte and the electrode is avoided, preventing the decomposition of electrolytes and formation of HF, in tune improving the interfacial stability [9] .…”

“…The formation of a stable cathode electrolyte interface (CEI) has been recognized as a promising strategy to improve the capacity retention of LNMO. [1,[5][6][7][8] In this manner, a direct contact between the electrolyte and the electrode is avoided, preventing the decomposition of electrolytes and formation of HF, in tune improving the interfacial stability. [9] The realization of a well-designed CEI, being a good Li + -conductor and providing protection, has been one of the main focuses of research during recent years.…”

Study on the (trimethoxysilyl) naphthalene electrolyte additive for enhancing electrochemical performance of LiNi0.5Mn1.5O4 cathode for Li-ion battery

“…By adding appropriate additives to the electrolyte, a protective film can be formed on the LNMO's surface. As previous reported, the siloxane (-Si-O-) derivatives can scavenge HF in electrolyte and carbon-carbon double bond (-C=C-) is favorable for electrochemical polymerization [5][6][7]. Hence, (Trimethoxysilyl)naphthalene (TMSN) containing Si-O and C=C groups was used as the electrolyte additive in conventional carbonate electrolytes to enhance the LNMO's electrochemical performances.…”