Electrochemical deposition mechanism of sodium and potassium

Abstract

Sodium and potassium metal batteries are being developed and studied enthusiastically by researchers, but the electrochemical deposition mechanism of sodium and potassium are still elusive and considered as analogs of the lithium version. In this study, it is found that the deposition of sodium and potassium are different from lithium. During deposition, cations get electrons and turn into metal deposited beneath the solid electrolyte interphase (SEI), and consequently the SEI is subject to the pressure from the metal around the deposition sites. Under the pressure, the SEI of lithium is strong enough to keep its integrity, which leads to the root growth of deposits. The lithium deposits are whiskers with the diameter of submicrometer and can be blocked by separators with the pores of dozens of nanometers. By contrast, the SEIs of sodium and potassium are weak and break into fragments under the pressure, and the subsequent deposition occur on the metal surfaces. The deposits grow into micro-scale granules and spread through the nanopores of separators, which causes the short circuit.