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.

Novel composite gel polymer electrolytes exhibiting high ionic conductivity and good mechanical stability are prepared, and their electrochemical properties are characterized. As lithium ion sources of a single ion conductor, the core‐shell structured SiO2(Li+) nanoparticles with uniform spherical shape are synthesized and used as functional fillers in the composite gel polymer electrolytes. By using the composite gel polymer electrolytes, the lithium powder polymer batteries composed of a lithium powder anode and a layered lithium vanadate (LiV3O8) cathode are assembled and their cycling performance is evaluated. The resulting lithium powder polymer batteries deliver a high discharge capacity of 264 mAh g−1 at room temperature and exhibit good capacity retention even at high current rates. The morphological analysis of the lithium powder anode reveals that the dendrite growth during cycling can be effectively suppressed by using the composite gel polymer electrolytes.

Poly(3,4-ethylenedioxythiophene)-co-poly(ethylene glycol) copolymer was coated onto lithium metal as a protective layer. The thin conductive polymer with strong adhesion to the lithium electrode suppressed the corrosion of the lithium metal and stabilized the interface of the lithium electrode in prolonged contact with the organic electrolyte. The conductive polymer coating on the lithium metal caused the capacity retention of the Li/LiCoO2 cell to increase from 9.3% to 87.3% after 200 cycles compared to the cell with the pristine lithium electrode. The improvement in cycling stability is attributed to the conductive polymer coating suppressing lithium dendrite growth and the deleterious reaction between the lithium electrode and the electrolyte solution during cycling.

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Core-shell structured SiO 2 nanoparticles containing poly(lithium acrylate) in the shell were synthesized and used as functional fillers in composite polymer electrolytes for lithium-ion polymer cells. The composite polymer electrolytes prepared with SiO 2 (Li + ) particles exhibited high ionic conductivity, good thermal stability, and favorable interfacial characteristics. By using these composite polymer electrolytes, lithium-ion polymer cells composed of a graphite negative electrode and a LiNi 0.6 Co 0.2 Mn 0.2 O 2 positive electrode were assembled, and their cycling performance was evaluated. The cells assembled with composite polymer electrolytes containing a proper amount of SiO 2 (Li + ) particles exhibited good cycling performance at both at ambient and elevated temperatures. Lithium-ion polymer cells which employ polymer electrolytes have been widely investigated for applications in portable electronic devices, electric vehicles, and energy storage systems.1-4 Although the ionic conductivities of gel polymer electrolytes usually exceed 10 −3 S cm −1 at ambient temperature, the host polymers usually lose their mechanical strength when they are plasticized by organic solvents. Thus, porous polyolefin separators are now being used to provide mechanical support in commercialized lithium-ion polymer batteries. In order to obtain gel polymer electrolytes with enhanced mechanical strength, inert inorganic fillers such as SiO 2 , Al 2 O 3 , TiO 2 , and BaTiO 3 have been incorporated into the gel polymer electrolytes. [5][6][7][8][9][10][11][12][13][14] In these composite polymer electrolytes, the inorganic particles improve the mechanical properties of the gel polymer electrolytes through physical action without directly contributing to the lithium-ion transport process. In our previous studies, core-shell structured SiO 2 particles containing poly(lithium 4-styrene sulfonate) in the shell were synthesized and used in preparing Li + -conducting composite polymer electrolytes. [15][16][17][18] In this study, we synthesized core-shellstructured SiO 2 particles containing poly(lithium acrylate) in the shell, because poly(lithium acrylate) is expected to be more compatible with carbonate-based liquid electrolytes such as ethylene carbonate (EC) and diethylene carbonate (DEC). Unlike conventional ceramic fillers, the core-shell-structured SiO 2 particles containing poly(lithium acrylate) act as a source of Li + ions in the composite polymer electrolyte, because mobile Li + ions dissociate out of the shell of the particles. The SiO 2 (Li + ) nanoparticles were incorporated into a poly(vinylidene fluoride-co-hexafluoropropylene) (P(VdF-co-HFP)) matrix polymer to make a thin porous composite polymer membrane, and the membrane was activated by soaking with liquid electrolyte to form the composite polymer electrolyte. The effect of the amount of coreshell SiO 2 (Li + ) particles was investigated in detail in order to provide the composite polymer electrolyte with high ionic conductivity, good thermal stability, and favo...