Commercial carbon anode material surface-modified by spinel lithium titanate for fast lithium-ion interaction
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Research Letter
Commercial carbon anode material surface-modified by spinel lithium titanate for fast lithium-ion interaction Lung-Hao Hu
, Department of Mechanical and Electro-Mechanical Engineering, National Sun Yat-sen University, Kaohsiung 804, Taiwan
Address all correspondence to Lung-Hao Hu at [email protected] and [email protected] (Received 7 November 2019; accepted 10 December 2019)
Abstract This research utilizes anatase TiO2 incorporated with lithium salt via a simple wet physical method to surface-modified the commercial graphite to form the lithium titanate/graphite composite coated with an amorphous carbon layer on its surface (the double core–shell structure) to enhance its surface conductivity. This double core–shell structure provides a stable specific capacity about 280 mAh/g under the high current density, 2.25 A/g with 15% capacity retention decay. Its intercalation potential is below 1 V that is much lower than that of 1.55 V, the intercalation potential of spinel Li4Ti5O12, to make higher power and energy density for a full cell.
Introduction The commercial carbon anode material that has been widely utilized for lithium (Li)-ion battery is graphite due to its low cost, low redox potential, and simple process. Its theoretical capacity is relatively high, about 372 mAh/g;[1] however, when the charging or discharging rate applied is higher, this could cause the graphene interlayer expansion and contraction continuously. Finally, the graphene interlayer of graphite would collapse owing to the volume change.[1–5] Therefore, the rate capability of the commercial anode material, graphite is poor to be not suitable for the high power devices. The mechanism of charging and discharging for the Li-ion battery at the anode is shown in reaction (1). During one Li-ion intercalated in or de-intercalated out from the graphite anode, there is one electron moving to the load.[6] 6C + x Li+ + xe− Lix C6 , where x = 1 in Lix C6
(1)
Lithium titanate (LTO, Li4Ti5O12) is the other commercially available anode material been widely studied, and its advantage is able to sustain high current discharging and charging owing to its spinel structure.[7–9] This anode material is so-called a zerostrain material without volume change during Li-ion intercalation/de-intercalation. Compared with the traditional graphite anode material, the potential (1.55 V versus Li/Li+) for Li-ion intercalation is relatively higher than that of graphite avoiding the formation of solid-electrolyte interphase (SEI) and lithium dendrite, and the decomposition of organic electrolyte. However, the higher potential for Li-ion intercalation of LTO is a drawback to cause a low working voltage of a full cell battery. The advantages of spinel LTO as the anode for the Li-ion battery are good rate capability, low cost, and highly safety issue; however, its drawbacks are its high working voltage ∼1.55 V and low
theoretical capacity and conductivity. The commercial anode material for the Li-ion battery is the artificial graphite whose advantages a
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