Characterisation and modelling of potassium-ion batteries

Potassium-ion batteries (KIBs) are emerging as a promising alternative technology to lithium-ion batteries (LIBs) due to their significantly reduced dependency on critical minerals. KIBs may also present an opportunity for superior fast-charging compared to LIBs, with significantly faster K-ion electrolyte transport properties already demonstrated. In the absence of a viable K-ion electrolyte, a full-cell KIB rate model in commercial cell formats is required to determine the fast-charging potential for KIBs. However, a thorough and accurate characterisation of the critical electrode material properties determining rate performance-the solid state diffusivity and exchange current density-has not yet been conducted for the leading KIB electrode materials. Here, we accurately characterise the effective solid state diffusivities and exchange current densities of the graphite negative electrode and potassium manganese hexacyanoferrate <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub><mml:mrow><mml:mi>K</mml:mi></mml:mrow> <mml:mrow><mml:mn>2</mml:mn></mml:mrow> </mml:msub> <mml:mi>Mn</mml:mi> <mml:mrow><mml:mo>[</mml:mo> <mml:mrow><mml:mi>Fe</mml:mi> <mml:msub> <mml:mrow><mml:mrow><mml:mo>(</mml:mo> <mml:mrow><mml:mi>CN</mml:mi></mml:mrow> <mml:mo>)</mml:mo></mml:mrow> </mml:mrow> <mml:mrow><mml:mn>6</mml:mn></mml:mrow> </mml:msub> </mml:mrow> <mml:mo>]</mml:mo></mml:mrow> </mml:math> (KMF) positive electrode, through a combination of optimised material design and state-of-the-art analysis. Finally, we present a Doyle-Fuller-Newman model of a KIB full cell with realistic geometry and loadings, identifying the critical materials properties that limit their rate capability.