Abstract
In this study, the use of a closo-borate salt as an electrolyte for lithium-ion batteries (LIB) was evaluated in a series of solvent systems. The lithium closo-borate salts are a unique class of halogen-free salts that have the potential to offer some advantages over the halogenated salts currently employed in commercially available LIB due to their chemical and thermal stability. To evaluate this concept, three different solvent systems were prepared with a lithium closo-borate salt to make a liquid electrolyte (propylene carbonate, ethylene carbonate:dimethyl carbonate, and 1-Butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide). The closo-borate containing electrolytes were then compared by utilizing them with three different electroactive electrode materials. Their cycle stability and performance at various charge/discharge rates was also investigated. Based on the symmetrical cell and galvanostaic cycling studies it was determined that the carbonate based liquid electrolytes performed better than the ionic liquid electrolyte. This work demonstrates that halogen free closo-borate salts are interesting candidates and worthy of further investigation as lithium salts for LIB.
Highlights
Lithium-ion batteries (LIB) have emerged as ubiquitous components of personal consumer electronics, electric vehicles, and grid storage owing to their high energy density. significant advances have been made to fine-tune and enhance the properties of cathode and anode materials, the electrolyte salt (LiPF6 ) used in many these systems has remained nearly constant since the rechargeable LIB was released by Sony in the early1990s [1]
In this report we evaluate the electrochemical properties of a halogen-free closo-borate salt (Li2B12H12) in three different liquid solvents (propylene carbonate, ethylene carbonate:dimethyl carbonate, and 1-Butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide)
All reagents were purchased from Fisher Scientific: propylene carbonate (PC), ethylene carbonate (EC), dimethyl carbonate (DMC), 1-Butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (BMIM-TFSI), titanium disulfide (TiS2 ), lithium titanate (Li4 Ti5 O12, LTO), perylenetetracarboxylic diimide (PTCDI), decaborane, lithium borohydride (LiBH4 ), and acetylene black (AB)
Summary
Lithium-ion batteries (LIB) have emerged as ubiquitous components of personal consumer electronics, electric vehicles, and grid storage owing to their high energy density. significant advances have been made to fine-tune and enhance the properties of cathode and anode materials, the electrolyte salt (LiPF6 ) used in many these systems has remained nearly constant since the rechargeable LIB was released by Sony in the early1990s [1]. LiPF6 has a low ionic conductivity in the solid-state so it must be dissolved in a nonaqueous solvent to facilitate its dissociation and produce mobile Li+ in solution to facilitate charging and discharging. Manufacturers have developed a series of carbonate based solvent systems and additives to enhance cycle stability, ionic conductivity, thermal stability, and solid electrolyte interface (SEI) formation. The carbonates used are flammable and can act as a fuel source if there is a short circuit or thermal runaway in a battery. This has led to the investigation of ionic liquids as the solvent medium or additives for LIB to reduce or eliminate the flammable component of the electrolyte system [2]
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