Hoogil Lee

Dopamine as a Novel Electrolyte Additive for High-Voltage Lithium-Ion Batteries.

Dopamine, which can be electrochemically oxidized to polydopamine on cathode surface, was introduced as an electrolyte additive for high-voltage lithium-ion batteries (LIBs). The addition of 0.1 wt % dopamine to the electrolyte led to the formation of a polydopamine-containing layer on the cathode, thereby resulting in suppression of the oxidative decomposition of the electrolyte during high-voltage operation (up to 4.5 V) of a LiNi1/3Co1/3Mn1/3O2/artificial graphite cell. The addition of dopamine to the electrolyte improved the capacity retention of the cell from 136 to 147 mAh g(-1) after 100 cycles at a rate of 1 C and a cutoff voltage of 4.5 V, while the cycle performance and rate capability with a cutoff voltage of 4.3 V were comparable to those of the cell without dopamine. Further evidence of the positive impact of dopamine on high-voltage LIBs was the lower DC-IRs and AC impedances, as well as the retention of the cathode morphology even after operation at 4.5 V.

Effects of an Integrated Separator/Electrode Assembly on Enhanced Thermal Stability and Rate Capability of Lithium-Ion Batteries

To improve the rate capability and safety of lithium-ion batteries (LIBs), we developed an integrated separator/electrode by gluing polyethylene (PE) separators and electrodes using a polymeric adhesive (poly(vinylidene fluoride), PVdF). To fabricate thin and uniform polymer coating layers on the substrate, we applied the polymer solution using a spray-coating technique. PVdF was chosen because of its superior mechanical properties and stable electrochemical properties within the voltage range of commercial LIBs. The integrated separator/electrode showed superior thermal stability compared to that of the control PE separators. Although PVdF coating layers partially blocked the porous structures of the PE separators, resulting in reduced ionic conductivity (control PE = 0.666 mS cm-1, PVdF-coated PE = 0.617 mS cm-1), improved interfacial properties between the separators and the electrodes were obtained due to the intimate contact, and the rate capabilities of the LIBs based on integrated separators/electrodes showed 176.6% improvement at the 7 C rate (LIBs based on PVdF-coated and control PE maintained 48.4 and 27.4% of the initial discharge capacity, respectively).

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.