Electrochemical cell

A method of manufacturing a sodium electrochemical cell which (i) comprises a negative electrode comprising sodium and a sodium-ion ionic liquid electrolyte having a sodium-ion concentration that is no less than 75% of its saturation limit in the electrolyte and is at least 40 mol %, the electrolyte comprising a phosphonium-based organic salt, and (ii) supports a current density at the negative electrode of at least 500 μA/cm2, the method comprising (i) bringing into contact with the negative electrode the sodium-ion ionic liquid electrolyte, and (ii) performing a polarisation cycle of the cell so as to form at the negative electrode a solid-electrolyte interphase (SEI) layer.

A sodium rechargeable battery that supports a current density at the negative electrode of at least 500 μA/cm2, the battery comprising (i) a negative electrode comprising sodium, (ii) a positive electrode and (iii) a sodium-ion ionic liquid electrolyte having a sodium-ion concentration that is no less than 75% of its saturation limit in the electrolyte and is at least 40 mol %, wherein the negative electrode has a solid-electrolyte interphase (SEI) layer formed as a result of the battery having undergone a polarization cycle, and wherein the electrolyte comprises a phosphonium-based organic salt.