Electrochemical performance of all-solid-state lithium secondary batteries using Li 4 Ti 5 O 12 electrode and Li 2 S-P 2
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All-solid-state Li–In/Li4Ti5O12 cells using Li2S–P2S5 solid electrolytes were assembled to investigate their electrochemical properties in the wide voltage range of 0–3 V (versus Li). The Li/Li4Ti5O12 cells using 1 M LiPF6 in ethylene carbonate and diethyl carbonate were fabricated for comparison with the all-solid-state cells. The capacity of the all-solid-state cell using the 70Li2S27P2S53P2O5 (mol%) solid electrolyte decreased with an increase in the current density as well as the cell using the liquid electrolyte. However, the allsolid-state cell was charged and discharged even at a high current density of 10 mA/cm2. The all-solid-state cell was cycled at 1.3 mA/cm2 and retained 90% of the first reversible capacity of about 120 mAh/g after 500 cycles. The all-solid-state cell cycling at 100 C showed the small overpotential and reversible capacity of about 120 mAh/g at 13 mA/cm2. I. INTRODUCTION
All-solid-state lithium secondary batteries have been studied as new energy storage devices with safety and reliability. All-solid-state batteries using sulfide-based solid electrolytes have been developed during last 15 years.1–6 We have focused on the fact that Li2S–P2S5 glass-ceramics have high lithium-ion conductivities and applied the 80Li2S20P2S5 (mol%) glass-ceramic of about 103 S/cm at room temperature as the solid electrolyte to the allsolid-state lithium batteries.3,7 The all-solid-state batteries showed the good cyclability under current densities less than 0.1 mA/cm2. During our search for the solid electrolytes with higher lithium-ion conductivities, we have recently found that the 70Li2S(30 x)P2S5xP2O5 glassceramics show remarkably high lithium-ion conductivities of about 3 103 S/cm.8,9 We have also searched electrode materials applicable to all-solid-state lithium batteries with Li2S–P2S5 solid electrolytes. Lithium titanate spinel (Li4Ti5O12) is a promising negative electrode because the material showed the flat voltage profiles at 1.55 V and excellent cycling performance in the cell using liquid electrolytes.10 In addition, Li4Ti5O12 exhibits the negligible volume change during cycling, and these features of Li4Ti5O12 are suitable for the negative electrode of all-solid-state cells. In fact, the all-solid-state Li–In/Li4Ti5O12 cells using Li2S–P2S5 solid electrolytes cycled in the voltage range of 1.0–2.0 V (versus Li) at a current density of 0.064 mA/cm2 and retained the reversible capacity of more than 100 mAh/g over 300 cycles.11 However, the all-solid-state cells a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2010.0199
1548
http://journals.cambridge.org
J. Mater. Res., Vol. 25, No. 8, Aug 2010 Downloaded: 13 Mar 2015
showed a limited discharge capacity at high current densities because a large overpotential was observed during discharge process.12 The overpotential was ascribed to the resistance related to the lithium-ion transfer at the electrode–electrolyte interface. We presumed that the interfacial resistance is affected by the l
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