Eung-Ju Lee

Development of Microstrain in Aged Lithium Transition Metal Oxides

Cathode materials with high energy density for lithium-ion batteries are highly desired in emerging applications in automobiles and stationary energy storage for the grid. Lithium transition metal oxide with concentration gradient of metal elements inside single particles was investigated as a promising high-energy-density cathode material. Electrochemical characterization demonstrated that a full cell with this cathode can be continuously operated for 2500 cycles with a capacity retention of 83.3%. Electron microscopy and high-resolution X-ray diffraction were employed to investigate the structural change of the cathode material after this extensive electrochemical testing. It was found that microstrain developed during the continuous charge/discharge cycling, resulting in cracking of nanoplates. This finding suggests that the performance of the cathode material can be further improved by optimizing the concentration gradient to minimize the microstrain and to reduce the lattice mismatch during cycling.

Progress in High-Capacity Core–Shell Cathode Materials for Rechargeable Lithium Batteries

High-energy-density rechargeable batteries are needed to fulfill various demands such as self-monitoring analysis and reporting technology (SMART) devices, energy storage systems, and (hybrid) electric vehicles. As a result, high-energy electrode materials enabling a long cycle life and reliable safety need to be developed. To ensure these requirements, new material chemistries can be derived from combinations of at least two compounds in a secondary particle with varying chemical composition and primary particle morphologies having a core-shell structure and spherical cathode-active materials, specifically a nanoparticle core and shell, nanoparticle core and nanorod shell, and nanorod core and shell. To this end, several layer core-shell cathode materials were developed to ensure high capacity, reliability, and safety.

High dispersion of TiO2 nanocrystals within porous carbon improves lithium storage capacity and can be applied batteries to LiNi0.5Mn1.5O4

A new and simple strategy was developed to effectively disperse titanium dioxide (TiO2) nanocrystals into porous carbon (PC), and a series of hierarchical PC–TiO2 composites with different architectures were synthesized. By varying the amount of TiO2, from 30 wt% to 64 wt%, the lithium storage capacity of PC–TiO2 could be controllably varied from 546 mA h g−1 to 446 mA h g−1 under a current density of 50 mA g−1. Also, very stable cycling performances and rate capabilities could be obtained at the rates of 50 mA g−1 to 1600 mA g−1. By further increasing the content of TiO2 to 93%, another new composite of TiO2–C was also prepared and it demonstrated a storage capacity of 352 mA h g−1 at 50 mA g−1, which is much higher than that for most reported TiO2 materials. Based on these results, new full cells with a LiNi0.5Mn1.5O4 cathode, such as PC–TiO2/LiNi0.5Mn1.5O4, were successfully assembled and investigated. This full cell not only delivered a high energy density of 413 W h kg−1 but also showed a good rate capability and an energy retention of 90.5% over 100 cycles.