A Single-Phase, All-Solid-State Sodium Battery Using Na_(3?x)V_(2?x)Zr_x(PO_4)_3 as the Cathode, Anode, and Electrolyte

摘要

Many studies of all-solid-state lithium-ion batteries have been performed due to the high energy density and small radii of the lithium ion.[1–4] However, the much lower price of sodium compared with lithium gives the former a large advantage; therefore, there is a compelling reason to study sodium-ion batteries.[ 5,6] Although there have been some reports of all-solidstate sodium-ion batteries using a sulfide-based electrolyte,[6–9] there have been only a limited number of publications regarding all-solid-state sodium-ion batteries incorporating inorganic oxide-based solid electrolytes, and these reports involve high temperature operation (above 473 K).[10–12] One challenge associated with the fabrication of all-solid-state sodium-ion batteries is the interfacial resistance between the electrolyte and the electrode. In order to ensure good contact between the electrode and electrolyte, high temperature sintering is typically employed, particularly in the case of an oxide-based solid electrolyte. However, this process potentially brings a high-resistive layer between the electrode and electrolyte as a consequence of reactions induced in the various materials.[ 1,13] The large interfacial resistance lowers the capability of the solid-state battery even if the bulk conductivity of the electrolyte is very high.[8,14–16] The sodium super ionic conductor(NASICON)-related phosphate, Na_3V_2(PO_4)_3, is a promising electroactive material, and can potentially serve as the anode and cathode in a battery, based on its redox reactions at low potentials (V~(3+)/V~(2+)) and high potentials (V~(3+)/V~(4+)), respectively.[ 10,17] Noguchi et al. first reported a symmetrical “all- NASICON cell,” using Na_3V_2(PO_4)_3 as the active material and Na_3Zr_2Si_2PO_(12) as the solid electrolyte and operating at room temperature.[10] However, in spite of this identical crystal structure, this device still has a high-resistive interface because the Na_3V_2(PO_4)_3 must be attached via relatively low temperature (973 K) calcination (to prevent the formation of a reaction layer that is otherwise generated above 1073 K).