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2009, 113, 6324–6326 Published on Web 03/31/2009
Study on the Theoretical Capacity of Spinel Lithium Titanate Induced by Low-Potential Intercalation Hao Ge,* Ning Li, Deyu Li, Changsong Dai, and Dianlong Wang Department of Applied Chemistry, Harbin Institute of Technology, Harbin 150001, P. R. China ReceiVed: February 24, 2009; ReVised Manuscript ReceiVed: March 23, 2009
The view that the theoretical capacity of spinel Li4Ti5O12 is limited by the number of available octahedral sites to accommodate lithium ions is debated. Combining the electrochemical and XRD results with the crystal structure of Li4Ti5O12, we demonstrate the corresponding reaction mechanism of the low-potential intercalation behavior of Li4Ti5O12 and modify the classical viewpoint on the theoretical capacity of Li4Ti5O12. The theoretical capacity of Li4Ti5O12 is limited by the number of tetravalent titanium ions, but not the octahedral or tetrahedral sites to accommodate lithium ions in the voltage range of 2.5 to 0.01 V, corresponding to 293 mAhg-1, but not 175 mAhg-1. Despite lithium-ion batteries having obvious advantages over nickel-cadmium and lead-acid cells, i.e., superior energy density and lower toxicity, there are still some safety concerns with the carbon anode and a safer alternative which can offer the same performance would be preferable.1-3 Spinel oxides Li4Ti5O12, the end member of Li1+xTi2-xO4 (0 e x e 1/3),4 has been studied as a candidate of a negative active electrode for rechargeable lithium batteries due to its excellent cycle life and safety compared to carbon materials.5-7 The theoretical capacity8 of Li4Ti5O12 was considered as 175 mAhg-1, which has been quoted by almost all the papers on Li4Ti5O12. Because the reversible capacity of Li4Ti5O12 is close to 175 mAhg-1 in the voltage range of 2.5∼1.0 V, most researchers have thought that lithium ions can not intercalate into Li4Ti5O12 at low potential (
