科研之友
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摘要
Sodium-ion batteries potentially provide the opportunities to realize the energy storage system beyond the state-of-the-art lithium-ion batteries, though at present their performance is limited partly due to lack of suitable positive electrode materials. NASICON-type Na3V2(PO4)(3) is a promising candidate for the positive electrode materials because of its high capacity and high operating potential, however, the electrode reaction of Na1+2xV2(PO4)(3) (0 <= x <= 1) including a biphasic region is not yet fully understood. Here, in order to clarify the microscopic mechanism of the biphasic reaction, the reaction entropy of the electrochemical cell including the Na1+2xV2(PO4)(3) positive electrode was measured using the potentiometric method. The temperature-dependent open-circuit voltage reveals that the reaction entropy is almost constant for 0.1 <= x <= 0.9. The constant reaction entropy of the electrochemical cell suggests that the electrode reaction proceeds through the boundary migration between the Na-rich and-poor phases without substantial change in the configurational entropy.
- 出版日期2016-4
