Reviving bipolar construction to design and develop high-energy sodium-ion batteries

With increased penetration of portable electronics and renewable energy sources, the demand for safer, energy-dense, and environmentally friendly batteries has recently risen. Sodium-ion batteries, believed to be safer and cheaper than Li-ion batteries, are lagging in energy density due to their higher standard reduction potential (−2.713 V) than lithium (−3.040 V). To improve the energy density, the sodium-ion batteries are designed in a bipolar configuration, where the cathode and anode are coated on opposite sides of the same current collector. The shared current collector eliminates the use of the tabs and wires interconnection and hence improves the energy density of the sodium-ion Battery. Bipolar sodium-ion batteries are believed to outperform conventional monopolar sodium-ion batteries. The performance of the bipolar sodium-ion Battery critically depends on the choice of the bipolar substrate, active electrode materials, electrolyte, and thickness and form factor of the cell. Moreover, the bipolar battery design has a major challenge of building the cell without electrolyte leakage and intermixing between the cells' interconnections. The present review mainly focuses on selecting bipolar substrate, anode, and active cathode material, design challenges, and their plausible solutions.