Application of P2-Na_2/3Ni_1/3Mn_2/3O₂ Electrode to All-Solid-State 3 V Sodium(-Ion) Polymer Batteries

Abstract

In this study, all-solid-state sodium batteries with dry polymer electrolytes are demonstrated based on Na half-cell optimization for the stable operation of a layered oxide positive electrode, P2-Na2/3[Ni1/3Mn2/3]O2, and a hard carbon negative electrode at 60 °C. In all-solid-state batteries, the dry-polymer electrolyte does not penetrate the pores of the composite electrode; thus, dispersibility of the active material, conductive carbon, and binder polymer inside the composite electrode is essential to obtain a stable charge–discharge reaction. Using Ketjen black as a conductive carbon, a uniformly dispersed composite electrode was successfully fabricated for an acceptable charge–discharge reaction. Instead of a conventional polyvinylidene fluoride binder, a polymer electrolyte must be used as a binder polymer to provide an effective ionic conduction path inside the composite electrode. All-solid-state Na // P2-Na2/3[Ni1/3Mn2/3]O2 batteries exhibited excellent cycle performance even at 60 °C, while deterioration was more pronounced in the liquid electrolyte at the same temperature. The capacity retention of the P2-Na2/3[Ni1/3Mn2/3]O2 // hard carbon cell was further improved by coating P2-Na2/3[Ni1/3Mn2/3]O2 with Al-oxide.

Scalable Glass-Fiber-Polymer Composite Solid Electrolytes for Solid-State Sodium–Metal Batteries

“…The CSE begins to reach a current density of ∼200 μA cm –2 , where the electrolyte polarization limits active material utilization, shown by the cycling data for the 4.5 mg sample at C/2. The all-solid-state cell design is able to show relatively stable cycling performance for the different current densities discussed, although the capacity fade is worse than what would be expected in a liquid electrolyte cell at the given rates …”

“…To test the critical current density of the CSE, sodium symmetric cells were cycled at increasing current densities ranging from 0.03 to 1.0 mA cm –2 with 0.03 mA cm –2 steps every 5 cycles. The voltage time profile for the critical current density measurement is plotted in Figure C, revealing a linear increase in overpotential with the applied current density until the cell was found to short-circuit at 0.67 mA cm –2 , where it exhibited an overpotential of 1.1 V. The ohmic response observed by the cell can be attributed to the stability of the SEI layer formed at the sodium–metal interface . The complex impedance spectra were collected after each current density and are plotted in Figure D, which reveals a consistent decrease in cell resistance until current densities are >0.4 mA cm –2 .…”

“…The voltage time profile for the critical current density measurement is plotted in Figure 7C, revealing a linear increase in overpotential with the applied current density until the cell was found to short-circuit at 0.67 mA cm −2 , where it exhibited an overpotential of 1.1 V. The ohmic response observed by the cell can be attributed to the stability of the SEI layer formed at the sodium−metal interface. 36 The complex impedance spectra were collected after each current density and are plotted in Figure 7D, which reveals a consistent decrease in cell resistance until current densities are >0.4 mA cm −2 . At higher current densities, the bulk impedance begins to increase, suggesting the stack pressure of the coin-cell format becomes a limiting factor.…”

“…Future work will investigate stable cycling performance for the different current densities discussed, although the capacity fade is worse than what would be expected in a liquid electrolyte cell at the given rates. 36 The importance of calendaring is examined in Figure 8B using both calendared and uncalendared electrodes and by examining the performance at different current densities. The uncalendared electrodes show marginally better cathode material utilization at higher rates, but the most noticeable difference has to do with the capacity retention over cycling.…”

Research and Development of Novel Secondary Batteries in Japan

“…In addition to these batteries, the VSI also illustrates novel materials development, theoretical calculations, and characterization for other secondary batteries, such as Li-ion and Na-ion batteries. − …”