Highly Improved Rate Capability for a Lithium-Ion Battery Nano-Li4Ti5O12 Negative Electrode via Carbon-Coated Mesoporous Uniform Pores with a Simple Self-Assembly Method

Abstract

A mesostructured spinel Li 4 Ti 5 O 12 (LTO)-carbon nanocomposite (denoted asMeso-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-blockpoly(ethylene oxide) (PI-b -PEO) with a sp 2 -hybridized carbon-containing hydrophobic block is employed as a structure-directing agent. Then the assembled composite material is crystallized at 700 °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 ratecapabilities. The carbon-coated mesoporous structure enables highly improved electronic conductivity and signifi cantly 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.

Comparative study of carbon free and carbon containing Li4Ti5O12 electrodes

“…Song et al [14] and Kim et al [15] both used LTO particles from simple solid state synthesis of TiO2 and Li2CO3 starting materials producing relatively large particle size up to 1 µm. On the other hand, carbon additives or carbon coating has been earlier found to improve the performance of LTO electrodes when particle size has been close to our LTO particles (100-300 nm) [18] or surface area very large (68.7 m 2 g -1 ) [17]. Kim et al [15] explained progress of the lithium insertion reaction in carbon free LTO electrodes during charging by propagation of a conductive LTO front, i.e.…”

“…However, the published information of the necessity of carbon additives or carbon coating in LTO electrodes is inconsistent as for some LTO materials carbon free electrodes have shown worse rate capabilities when compared to carbon containing electrodes [17,18]. Here we study the performance of carbon free Li4Ti5O12 electrodes using two different LTO powders manufactured by a pilot scale process with different particle size and specific surface area.…”

Anodes – Materials for negative electrodes in electrochemical energy technology

“…NiO has been prepared as a composite with polypyrrole yielding substantially improved performance when compared with plain NiO [94]. Among several lithium titanium oxides (see [58]), Li 4 Ti 5 O 12 with a carbon coating has shown promising performance [95]. A review of the use of conversion materials with particular attention to metal oxides has been provided [96].…”

Molten Salt Assisted Self Assembly (MASA): Synthesis of Mesoporous Metal Titanate (CoTiO3, MnTiO3, and Li4Ti5O12) Thin Films and Monoliths

“…16,17,20 No small surfactant soft-templating method exists for the synthesis of mesoporous metal titanates in the literature. 16 Also note that the metal titanates form at high temperatures (250−350°C).…”

“…16,25−34 The formation of LLC mesophases using lithium salts can also be beneficial in the development of liquid crystalline gel-electrolytes 34 as well as in the development of lithium ion containing mesoporous metal oxides. 16,29−34 Note that many lithium metal oxides have been used as anode or cathode materials in lithium ion batteries.…”