Yoon-Sung Lee

Improvement of the Cycling Performance of LiNi0.6Co0.2Mn0.2O2 Cathode Active Materials by a Dual-Conductive Polymer Coating

LiNi0.6Co0.2Mn0.2O2 cathode materials were surface-modified by coating with a dual conductive poly(3,4-ethylenedioxythiophene)-co-poly(ethylene glycol) (PEDOT-co-PEG) copolymer, and their resulting electrochemical properties were investigated. The surface-modified LiNi0.6Co0.2Mn0.2O2 cathode material exhibited a high discharge capacity and good high rate performance due to enhanced transport of Li(+) ions as well as electrons. The presence of a protective conducting polymer layer formed on the cathode also suppressed the growth of a resistive layer and inhibited the dissolution of transition metals from the active cathode materials, which resulted in more stable cycling characteristics than the pristine LiNi0.6Co0.2Mn0.2O2 cathode material at 55 (o)C.

Improvement of the Cycling Performance and Thermal Stability of Lithium-Ion Cells by Double-Layer Coating of Cathode Materials with Al2O3 Nanoparticles and Conductive Polymer

We demonstrate the effectiveness of dual-layer coating of cathode active materials for improving the cycling performance and thermal stability of lithium-ion cells. Layered nickel-rich LiNi0.6Co0.2Mn0.2O2 cathode material was synthesized and double-layer coated with alumina nanoparticles and poly(3,4-ethylenedioxythiophene)-co-poly(ethylene glycol). The lithium-ion cells assembled with a graphite negative electrode and a double-layer-coated LiNi0.6Co0.2Mn0.2O2 positive electrode exhibited high discharge capacity, good cycling stability, and improved rate capability. The protective double layer formed on the surface of LiNi0.6Co0.2Mn0.2O2 materials effectively inhibited the dissolution of Ni, Co, and Mn metals from cathode active materials and improved thermal stability by suppressing direct contact between electrolyte solution and delithiated Li(1-x)Ni0.6Co0.2Mn0.2O2 materials. This effective design strategy can be adopted to enhance the cycling performance and thermal stability of other layered nickel-rich cathode materials used in lithium-ion batteries.

Unique core–shell structured SiO2(Li+) nanoparticles for high-performance composite polymer electrolytes

Core–shell structured SiO2 nanoparticles with controlled morphology were synthesized and used as functional fillers in Li+-conducting composite polymer electrolytes for lithium-ion polymer batteries. The composite polymer electrolytes prepared with poly(vinylidene fluoride-co-hexafluoropropylene) and core–shell SiO2(Li+) nanoparticles exhibited high ionic conductivity, good mechanical strength and favorable interfacial characteristics. Tests run on carbon/LiNi1/3Co1/3Mn1/3O2 cells with composite polymer electrolyte containing optimized SiO2(Li+) nanoparticles yielded excellent results in terms of capacity retention (95% after 100 cycles) and rate capability (167 mA h g−1 at 5 C rate).

Study on the cycling performance of LiNi0.5Mn1.5O4 electrodes modified by reactive SiO2 nanoparticles

We demonstrate a facile approach to improve the cycling stability of spinel LiNi0.5Mn1.5O4 materials by their surface modification. The cross-linked composite polymer electrolyte layer was formed on the surface of LiNi0.5Mn1.5O4 by radical polymerization between diethylene glycol diacrylate and SiO2 nanoparticles with reactive vinyl groups. The protective composite polymer layer formed on the LiNi0.5Mn1.5O4 materials suppressed the irreversible decomposition of the electrolyte at high voltages and reduced the dissolution of transition metals from the charged LiNi0.5Mn1.5O4 electrode into the electrolyte at elevated temperature, which resulted in more stable cycling characteristics than the pristine LiNi0.5Mn1.5O4 electrode.

Cross-linked Composite Gel Polymer Electrolyte using Mesoporous Methacrylate-Functionalized SiO2 Nanoparticles for Lithium-Ion Polymer Batteries.

Liquid electrolytes composed of lithium salt in a mixture of organic solvents have been widely used for lithium-ion batteries. However, the high flammability of the organic solvents can lead to thermal runaway and explosions if the system is accidentally subjected to a short circuit or experiences local overheating. In this work, a cross-linked composite gel polymer electrolyte was prepared and applied to lithium-ion polymer cells as a safer and more reliable electrolyte. Mesoporous SiO2 nanoparticles containing reactive methacrylate groups as cross-linking sites were synthesized and dispersed into the fibrous polyacrylonitrile membrane. They directly reacted with gel electrolyte precursors containing tri(ethylene glycol) diacrylate, resulting in the formation of a cross-linked composite gel polymer electrolyte with high ionic conductivity and favorable interfacial characteristics. The mesoporous SiO2 particles also served as HF scavengers to reduce the HF content in the electrolyte at high temperature. As a result, the cycling performance of the lithium-ion polymer cells with cross-linked composite gel polymer electrolytes employing methacrylate-functionalized mesoporous SiO2 nanoparticles was remarkably improved at elevated temperatures.

High performance composite polymer electrolytes for lithium-ion polymer cells composed of a graphite negative electrode and LiFePO4 positive electrode

Core–shell structured SiO2 particles with different core diameters were synthesized by radical polymerization of 4-styrenesulfonic acid sodium salt with vinyl-functionalized SiO2 core particles and were used as Li+ ion-conducting fillers in composite polymer electrolytes. Composite polymer electrolytes prepared with core–shell SiO2 particles exhibited high ionic conductivity exceeding 10−3 S cm−1 at room temperature and good mechanical properties, allowing the preparation of a free-standing film with a thickness of 30 μm. Lithium-ion polymer cells composed of graphite negative electrode, composite polymer electrolyte and LiFePO4 positive electrode were assembled, and their cycling performance was evaluated. Cells assembled with a composite polymer electrolyte containing core–shell SiO2 particles with a core diameter of 250 nm exhibited good cycling performance in terms of discharge capacity, capacity retention and rate capability.