A Novel LiTi2O4-XCx As Li-Ion Battery Anode Material
Authors: Li Da , Armstrong Anthony Robert , Irvine John T. S. 
Published: February 2020

As a result of their high energy density lithium-ion batteries have been widely applied in the fields of portable electronic, implantable organs, power tools, and more recently electric vehicles. Typically carbon is widely used as a conductive additive in electrode fabrication due to the low conductivity of the active materials, which has a negative effect on the volumetric and gravimetric energy density. As a result, exploration of new materials with high conductivity as electrodes for Li-ion batteries is highly desirable.

Titanium-based materials as lithium-ion battery negative electrode have been widely studied. The zero strain insertion leads to excellent reversibility (>10,000 times) and capacity retention rate; [1] the combination of high lithium mobility results in high rate ability of the batteries; [2] higher working potential (>1.2 V vs Li+/Li) brings better safety with no lithium metal deposition during discharging compared to the carbon anodes. [3] But the relatively low electric conductivity (e.g. Li4Ti5O12 is only 10-9 S·cm-1 at 20 ℃) limits their ability and low temperature applications.

LiTi2O4 adopting the ramsdellite structure was firstly fabricated by D.C. Johnston. [4] This structure consists of distorted TiO6 octahedra which connect together by sharing edges resulting in double linked columns. These columns form an open framework structure in which Li+ occupies 50% of the tetrahedral channel sites. Hence the remaining tetrahedral sites are available for Li+ insertion delivering a theoretical specific capacity of 161 mAh g-1 for complete reduction to Ti3+ and all tetrahedral sites occupied and presumably lithium could be extracted. For titanium ramsdellite series capabilities of 180 mAh·g-1 (theoretical 298 mAh·g-1) for Li2Ti3O7, 113 mAh·g-1 for LiTi2O4 and 320 mAh·g-1 (theoretical 335 mAh·g-1) for TiO2 under 0.25 mA·cm-2 has been obtained by Gover. [5]

Titanium oxycarbide, TiOxC1-x, with a rocksalt structure formed by TiC and TiO, with O and C atoms sharing the anion sites, has a high metallic conductivity. [6] Thus partial replacement of O by C in transition metal oxides opens up a range of new compositions that might be expected to yield important functional properties.

In this work a novel carbon doping strategy was used to successfully fabricate LiTi2O4-xCx with the Ramsdellite structure. Initially TiOxC1-x and Li2Ti3O7 were made as raw materials by solid reaction ans then the LiTi2O4-xCx was fabricated in Ar under specific temperature. After that its structure was characterised and electrochemical property was tested. Based on refiment of X-ray diffraction patterns, increased levels of carbon substitution led to an increase in a and b parameters with a contraction in c. The incorporation of carbon was further confirmed by mass spectroscopy/thermal analysis. The performance as a negative electrode material for lithium-ion batteries was enhanced by carbon substitution with increased rate capability and improved cycle ability. Especially for LiTi2O3.925C0.075 capacities of 151 mAh·g-1 and 67 mAh·g-1 could be obtained under discharging current densities of 100 mA·g-1 and 2000 mA·g-1 and capacity decreased by 5.57% after 100 cycles. This results from increased conductivity and reduced cell polarization.

Keywords: titanium carbide, lithium ion battery, carbon doping

Reference

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