Jiseon Jeong

Highly Adhesive and Soluble Copolyimide Binder: Improving the Long-Term Cycle Life of Silicon Anodes in Lithium-Ion Batteries

A highly adhesive and thermally stable copolyimide (P84) that is soluble in organic solvents is newly applied to silicon (Si) anodes for high energy density lithium-ion batteries. The Si anodes with the P84 binder deliver not only a little higher initial discharge capacity (2392 mAh g(-1)), but also fairly improved Coulombic efficiency (71.2%) compared with the Si anode using conventional polyvinylidene fluoride binder (2148 mAh g(-1) and 61.2%, respectively), even though P84 is reduced irreversibly during the first charging process. This reduction behavior of P84 was systematically confirmed by cyclic voltammetry and Fourier-transform infrared analysis in attenuated total reflection mode of the Si anodes at differently charged voltages. The Si anode with P84 also shows ultrastable long-term cycle performance of 1313 mAh g(-1) after 300 cycles at 1.2 A g(-1) and 25 °C. From the morphological analysis on the basis of scanning electron microscopy and optical images and of the electrode adhesion properties determined by surface and interfacial cutting analysis system and peel tests, it was found that the P84 binder functions well and maintains the mechanical integrity of Si anodes during hundreds of cycles. As a result, when the loading level of the Si anode is increased from 0.2 to 0.6 mg cm(-2), which is a commercially acceptable level, the Si anode could deliver 647 mAh g(-1) until the 300th cycle, which is still two times higher than the theoretical capacity of graphite at 372 mAh g(-1).

Effects of Lithium Bis(Oxalate) Borate as an Electrolyte Additive on High-Temperature Performance of Li(Ni 1/3 Co 1/3 Mn 1/3 )O 2 /Graphite Cells

The effects of electrolyte additives, lithium bis(oxalate)borate (LiBOB), fluoroethylene carbonate (FEC), vinylene carbonate (VC), 2-(triphenylphosphoranylidene) succinic anhydride (TPSA), on high-temperature storage properties of /graphite are investigated with coin-type full cells. The 1 wt.% LiBOB-containing electrolyte showed the highest capacity retention after high temperature () storage for 20 days, 86.7%, which is about 5% higher than the reference electrolyte, 1.15M lithium hexafluorophosphate () in ethylene carbonate/ethyl methyl carbonate (EC/EMC, 3/7 by volume). This enhancement is closely related to the formation of semi-carbonate compounds originated from anions, thereby resulting in lower SEI thickness and interfacial resistance after storage. In addition, the 1 wt.% LiBOB-containing electrolyte also exhibited better cycle performance at 25 and than the reference electrolyte, which indicates that LiBOB is an effective additive for high-temperature performance of /graphite chemistry.