Highly improved rate capability for a lithium-ion battery nano-Li 4Ti 5O 12 negative electrode via carbon-coated mesoporous uniform pores with a simple self-assembly method
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- Highly improved rate capability for a lithium-ion battery nano-Li 4Ti 5O 12 negative electrode via carbon-coated mesoporous uniform pores with a simple self-assembly method
- Kang, Eunae; Jung, Yoon Seok; Kim, Gi-Heon; Chun, Jinyoung; Wiesner, Ulrich; Dillon, Anne C.; Kim, Jin Kon; Lee, Jinwoo
- Block copolymer self-assembly; Capacity retention; Carbon nanocomposite; Charge and discharge; Charge transfer resistance; Conductive carbon; Electronic conductivity; Ethylene oxides; Free surfaces; High rate capability; Hydrophobic blocks; In-situ; Li-ion batteries; Lithium-ion battery; Mesoporous; Mesoporous structures; Mesostructured; Mesostructures; Negative electrode; Potential range; Pyrolyzed carbon; Rate capabilities; Reversible capacity; Self-assembly method; Sharp contrast; Solid electrolyte interphase; Structure directing agents; Uniform pore; Voltage window
- Issue Date
- WILEY-V C H VERLAG GMBH
- ADVANCED FUNCTIONAL MATERIALS, v.21, no.22, pp.4349 - 4357
- A mesostructured spinel Li4Ti5O12 (LTO)-carbon nanocomposite (denoted as Meso-LTO-C) with large (>15 nm) and uniform pores is simply synthesized via block copolymer self-assembly. Exceptionally high rate capability is then demonstrated for Li-ion battery (LIB) negative electrodes. Polyisoprene-block-poly(ethylene oxide) (PI-b-PEO) with a sp2-hybridized carbon-containing hydrophobic block is employed as a structure-directing agent. Then the assembled composite material is crystallized at 700 degrees C enabling conversion to the spinel LTO structure without loss of structural integrity. Part of the PI is converted to a conductive carbon that coats the pores of the Meso-LTO-C. The in situ pyrolyzed carbon not only maintains the porous mesostructure as the LTO is crystallized, but also improves the electronic conductivity. A Meso-LTO-C/Li cell then cycles stably at 10 C-rate, corresponding to only 6 min for complete charge and discharge, with a reversible capacity of 115 mA h g-1 with 90% capacity retention after 500 cycles. In sharp contrast, a Bulk-LTO/Li cell exhibits only 69 mA h g-1 at 10 C-rate. Electrochemical impedance spectroscopy (EIS) with symmetric LTO/LTO cells prepared from Bulk-LTO and Meso-LTO-C cycled in different potential ranges reveals the factors contributing to the vast difference between the rate-capabilities. The carbon-coated mesoporous structure enables highly improved electronic conductivity and significantly reduced charge transfer resistance, and a much smaller overall resistance is observed compared to Bulk-LTO. Also, the solid electrolyte interphase (SEI)-free surface due to the limited voltage window (>1 V versus Li/Li+) contributes to dramatically reduced resistance.
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