Effects of Lithium Bis(Oxalate) Borate as an Electrolyte Additive on High-Temperature Performance of Li(Ni1/3Co1/3Mn1/3)O2/Graphite Cells

음극 표면에 solid electrolyte interphase (SEI)를 형성하는 전해질 첨가제인 lithium bis(oxalate) borate (LiBOB), fluoroethylene carbonate (FEC), vinylene carbonate (VC), 2-(triphenylphosphoranylidene) succinic anhydride (TPSA)를 Li(Ni1/3Co1/3Mn1/3)O₂ (NCM)/graphite 전지에 도입하여 고온 저장 특성을 비교하였다. 각 전지를 50%의 충전상태(stage of charge, SOC)에서, 고온 저장( 60∘C , 20일) 시킨 이후의 용량 유지율을 확인한 결과, LiBOB 1 wt.%가 가장 우수한 용량 유지 특성(초기 방전용량 대비 86.7%)을 나타내었다. LiBOB 1 wt.%의 경우 고온 저장 전후의 전지 저항 증가 및 SEI 두께 변화가 가장 적었고, 이는 음극 SEI에 포함된 다량의 semi-carbonate 물질과 연관성이 높다고 판단된다. 또한, LiBOB 1 wt.%가 포함된 NCM/graphite 전지의 상온( 25∘C ) 및 고온수명( 60∘C ) 특성도 기준 전해액(1.15 M lithium hexafluorophosphate (LiPF6) in ethylene carbonate/ethyl methyl carbonate (EC/EMC, 3/7 by volume))보다 각각 6%와 9% 향상된 결과를 보여주었다. 따라서, LiBOB이 상온 성능을 동등 이상으로 유지하면서도 고온 특성을 개선할 수 있는 우수한 전해액 첨가제로 판단된다. 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 Li(Ni1/3Co1/3Mn1/3)O₂ /graphite are investigated with coin-type full cells. The 1 wt.% LiBOB-containing electrolyte showed the highest capacity retention after high temperature ( 60∘C ) storage for 20 days, 86.7%, which is about 5% higher than the reference electrolyte, 1.15M lithium hexafluorophosphate ( LiPF₆ ) 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 BOB⁻ 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 60∘C than the reference electrolyte, which indicates that LiBOB is an effective additive for high-temperature performance of Li(Ni1/3Co1/3Mn1/3)O₂ /graphite chemistry.