A layer structured titanate Cs 2Ti 5O 11·(1 + x)H 2O (x = 0.70) has been prepared in a solid state reaction using Cs 2CO 3 and anatase type TiO 2 at 900 °C. Ion exchange reactions of Cs + in the interlayer space were studied in aqueous solu tions. The single phases of Li+, Na+ and H+ exchange products were obtained. The three kinds of resulting titanates were evaluated for use as the cathodes in rechargeable sodium batteries after dehydrations by heating at 200°C in a vacuum. The electrochemical measurements showed that they exhibited the reversible Na+ intercalation-deintercalation in a voltage range of 0.5 - 3.5 V or 0.7 - 4.0 V. The Li+ exchange product showed the best performance of the discharge-charge capacities in this study. The initial Na+ intercalation-deintercalation capacities of the Li2Ti5O11 were 120 mAh/g and 100 mAh/g; the amounts of Na+ correspond to 1.9 and 1.6 of the formula unit, respectively. The titanates are nontoxic, inexpensive and environmentally benign.
Sodium ion batteries have emerged for the ideal alternative to the lithium ion batteries which have the problems of lithium availability and cost. We have studied the characterizations of layer structured titanates and Niobate [
The crystal structure of Cs2Ti5O11 is shown in
The layer structured titanate Cs2Ti5O11・(1 + x)H2O has been prepared in a solid state reaction using Cs2CO3, anatase type TiO2 at 900˚C according to a similar method reported by Grey et al. [
Powder X-ray diffraction (XRD) patterns were collected by a Rigaku Ultima IV diffractometer over 2θ range of 10˚ to 70˚ using graphite monochromatized CuKα radiation (λ = 0.15405 nm). The contents of Cs, Li and Na in the samples were determined by the atomic absorption method after dissolving the samples in a mixed acid solution with H2SO4 and HF. Dehydration processes were studied by TG-DTA at a heating rate of 10˚C/min. A cathode was formed of a
mixture of the titanate powder (80 wt%), acetylene black (10 wt%) and PTFE binder (10 wt%) pressed into a stainless steel grid under a pressure of 100 MPa. The electrolyte of the sodium cell was 1.0 mol/L NaClO4 solution of propylene carbonate (PC) and an anode was sodium metal. The cells were first discharge and cycled between 0.5 V and 3.5 V or 0.7 V and 4.0 V at 0.10 mA/cm2 in an argon-filled glove box at room temperature.
The XRD pattern of Cs2Ti5O11・(1 + x)H2O (
Compositions | a/nm | b/nm | c/nm | β/˚ |
---|---|---|---|---|
Cs2Ti5O11・1.7H2O | 2.470 (3) | 0.3785 (4) | 1.573 (2) | 123.7 (1) |
Li2Ti5O11・3.6H2O | 2.48 | 0.376 | 1.76 | 127 |
Na2Ti5O11・4.1H2O | 2.58 | 0.375 | 1.77 | 125 |
H2Ti5O11・3.3H2O | 2.53 | 0.375 | 1.76 | 125 |
The XRD pattern of the Li+ exchange product is shown in
The XRD pattern of the Na+ exchange product is shown in
The XRD pattern of the H+ exchange product is shown in
The Li+, Na+ and H+ exchange products were evaluated for use as the cathodes in rechargeable sodium batteries after dehydrations by heating at 200˚C for 1 hour in a vacuum.
The Li+ exchange product showed the best performance in the discharge-charge capacities. The higher performance of Li+ exchange titanate than Na+ exchange titanate may be attributed to the difference of ionic radius of Li+ and Na+. The smaller ion volume of Li+ than Na+ can provide a lager vacant space for the intercalation of Na+. It is expected that H+ exchange titanate has the largest vacant space for the intercalation of Na+ among the ion exchange titanates obtained in this study. However, the H+ exchange titanate showed the worst performance of the discharge-charge capacities. It is necessary to investigate the structural changes during the discharge-charge processes for further understanding of these cathode materials.
The studies of these titanates for lithium ion batteries are now under way and will be presented elsewhere.
In this study, we showed for the first time that the layer structure titanates derived from Cs2Ti5O11・(1 + x)H2O by ion exchange can be promising candidates for the cathode materials of sodium ion batteries. The initial Na+ intercalation-deintercalation capacities of the Li2Ti5O11 were 120 mAh/g and 100 mAh/g;
the amounts of Na+ intercalated and deintercalated were 1.9 and 1.6 of the formula unit, respectively. The titanates are nontoxic, inexpensive and environmentally benign.
Ohashi, M. (2018) Novel Cathode Materials for Sodium Ion Batteries Derived from Layer Structured Titanate Cs2Ti5O11∙(1 + x)H2O. Materials Sciences and Applications, 9, 526-533. https://doi.org/10.4236/msa.2018.96037