Yang-Kook Sun

Effects of Metal Ions on the Structural and Thermal Stabilities of Li [ Ni1 − x − y Co x Mn y ] O2 ( x + y ⩽ 0.5 ) Studied by In Situ High Temperature XRD

Highly crystalline Li[Ni 1-x-y Co x Mn y ]O 2 (x + y ≤ 0.5) (Li[Ni 0.6 Co 0.2 Mn 0.2 ]O 2 , Li[Ni 0.55 Co 0.15 Mn 0.3 ]O 2 , and Li[Ni 0.5 Co 0.25 Mn 0.25 ]O 2 ) were synthesized through a coprecipitation method. The capacities of the prepared samples were proportional to the amount of Ni in the host structure. The thermogravimetric analysis (TGA) and in situ high-temperature-X-ray diffraction (HT-XRD) analysis revealed that changes in the amount of manganese ions in the host structure profoundly affect the structural stability of the samples with x + y ≤ 0.5. Li[Ni 0.55 CoO 0.15 Mn 0.3 ]O 2 , containing the highest manganese content (y = 0.3), showed the most stable structural integrity among the samples as confirmed by in situ HT-XRD. The electrochemical performances of the samples in Ni amount (0.5 ≤ 1 - x - y ≤ 0.6) with the variation of Co (0.15 ≤ x ≤ 0.25) did not significantly vary under the test conditions (3.0-4.3 V). The small increase of Mn ions plays an important role in preservation of its initial structural symmetry during the high-temperature heating as well as electrochemical cycling. Furthermore, the structural stability has a relationship with the thermal stability and the electrochemical stability, especially at an elevated temperature (55°C). On the basis of the differential scanning calorimetry and TGA results, the Li[Ni 0.55 Co 0.15 Mn 0.3 ]O 2 sample demonstrated improved thermal stability compared to the other samples.

Characterization of Core-Shell Type Cathode Material in Li-ion Cells

Novel cathode material having a shell and core structure has been developed for Lithium Ion batteries. This study essentially involves the electrochemical performance and thermal stability of core-shell material and verifies the effects of the shell and core separately. It was observed that the capacity obtained of the shell was about 145mAh/g and that of core was about 190 mAh/g. The overall capacity of the core-shell composite electrode was 175 mAh/g. Electrochemical impedance spectroscopy was used to explain the possible interfacial phenomena occurring within the material during lithium intercalation-deintercalation processes. Thermal studies were also investigated using Differential Scanning Calorimeter (DSC).

Ionic Conductivities of Solid Polymer Electrolyte/Salt Systems for Lithium Secondary Battery : Electrostatic Potential Contribution

We establish a thermodynamic model of ionic conductivities model for solid polymer electrolyte/salt systems based on modified double lattice (MDL) model. The proposed model takes into account both the mobility and the charge interactions of the solid polymer electrolyte/salt systems. The interactions between Li ion and polymer molecules are described by electrostatic potential (EP) when Li ion is passing by a polymeric membrane. In comparison with experimental data, quantitative descriptions of the proposed model show better agreement for the given systems than those of existing models.