Abstract
We report, for the first time, a one-step, continuous synthesis of spherical lithium titanate (Li4Ti5O12, LTO)/graphene composites through direct aerosolization of a graphene oxide (GO) suspension mixed with Li and Ti precursors. The resulting crumpled graphene-sphere-supported LTO nanocrystals has a three-dimensional structure with a high electrical conductivity, a high surface area and good stability in electrolyte. The LTO/CG composite, as an anode in LIBs, exhibited excellent rate capability (for example, at a high current density of 5000 mA g−1 it delivered 60% of the capacity obtained at 12.5 mA g−1) and an outstanding cycling performance (a capacity retention of 88% after 5000 cycles at 1,250 mA g−1). The one-step, continuous synthesis of the LTO/graphene composite offers a high-producing efficiency compared with conventional multi-step preparations, and can be generally applied for synthesizing lithium metal oxides/graphene (cathode or anode) materials for lithium-ion batteries. Researchers have used ‘crumpled’ graphene spheres dotted with nanocrystals to boost the safety and performance of Li-ion batteries. Lithium titanate (Li4Ti5O12 or LTO) is a promising alternative to conventional Li-ion battery anodes that is less prone to dangerous short-circuit reactions, but it suffers from poor conductivity. Junhong Chen and co-workers from the University of Wisconsin-Milwaukee have developed a one-step synthetic technique to remedy this situation. By passing aerosolized graphene oxide and LTO precursors through a high-temperature furnace, normally flat graphene sheets transformed into crumpled spheres covered with LTO nanocrystals. The hollow, three-dimensional structure of this anode significantly improved LTO conductivity by shortening distances needed for charge transfer. Furthermore, the integrated composite prevents premature nanocrystal aggregation, giving rise to long device lifespans — prototype batteries retained 88% of their capacity after 5,000 recharge cycles. A one-step and continuous method to produce a spherical Li4Ti5O12/graphene composite for the lithium-ion battery anode is reported. The high conductivity and hollow structure of the crumpled graphene sphere greatly enhance the rate capability and cycling performance of the Li4Ti5O12 anode. This method provides a new and exciting approach for high-performance anode material design and fabrication.
Highlights
For the first time, a one-step, continuous synthesis of spherical lithium titanate (Li4Ti5O12, LTO)/graphene composites through direct aerosolization of a graphene oxide (GO) suspension mixed with Li and Ti precursors
LTO/crumpled graphene (CG) composite synthesis through aerosolization method The LTO/CG hybrid was produced by an aerosolization/hightemperature-induced GO crumpling and nanocrystal growth method
Because of the rapid evaporation of the solvents, the GO sheets were compressed into a crumpled sphere shape while LTO nanocrystals were simultaneously grown from precursors and assembled on the surface of graphene spheres
Summary
Lithium-ion batteries (LIBs) have a high-rate capacity and long cycle life, and are critical for many important applications, such as electric vehicles (EVs) and portable electronic devices.[1,2,3] The use of combustible graphite (especially in lithiated states) is highly risky in the application of EVs and hybrid EVs (HEVs); alternative anode materials with a higher power density, better stability, and higher safety performance are greatly needed and deserve greater scientific exploration.Compared with graphitic carbon, spinel lithium titanate Li4Ti5O12 (LTO) exhibits a relatively high lithium insertion/extraction voltage of ~ 1.55 V (vs Li+/Li), which prevents the formation of the solid electrolyte interphase (SEI) and suppresses lithium dendrite deposition on the surface of the anode (most electrolyte materials or solvents are reduced below 1 V), thereby greatly decreasing the short-circuit risk of the battery.[4,5,6,7,8] In addition, LTO possesses excellent Li ion insertion and removal reversibility with almost zero volume change during the charge/discharge process.[9,10] as demonstrated in previous studies, it is still a challenge to achieve good battery performance at high charge/discharge rates using LTO as the anode material because of the low electrical conductivity (o10 − 13 S cm − 1) of LTO,[11,12] and there have been many efforts to improve the rate capability and the cycling performance of LTO-based batteries. The LTO/CG composite, as an anode in LIBs, exhibited excellent rate capability (for example, at a high current density of 5000 mA g − 1 it delivered 60% of the capacity obtained at 12.5 mA g − 1) and an outstanding cycling performance (a capacity retention of 88% after 5000 cycles at 1,250 mA g − 1).
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