First-Principles Prediction of Potentials and Space-Charge Layers in All-Solid-State Batteries

As all-solid-state batteries (SSBs) develop as an alternative to traditional cells, a thorough theoretical understanding of driving forces behind battery operation is needed. We present a fully first-principles-informed model of potential profiles in SSBs and apply the model to the $\mathrm{Li}/\mathrm{LiPON}/{\mathrm{Li}}_x{\mathrm{CoO}}_2$ system. The model predicts interfacial potential drops driven by both electron transfer and ${\mathrm{Li}}^{+}$ space-charge layers that vary with the SSB’s state of charge. The results suggest a lower electronic ionization potential in the solid electrolyte favors ${\mathrm{Li}}^{+}$ transport, leading to higher discharge power.

Figure 1

The vacuum-aligned position of the electronic bands in lithium metal, LiPON, ${\mathrm{LiCoO}}_2$, and ${\mathrm{Li}}_{0.5}{\mathrm{CoO}}_2$ before contact. Occupied bands (VBM) are blue and unoccupied bands (CBM) are orange. Vacuum (dashed line) alignments and band gaps are indicated.

Figure 2

Fermi level referenced to the VBM ($E_F$, blue; left axis) and ${\mathrm{Li}}^{+}$ carrier defect concentrations (${\mathrm{Li}}_i^{+}$, orange and $V_{\mathrm{Li}}^{-}$, blue; right axis) as a function of ${\mu }_{\mathrm{Li}}$. Li metal and ${\mathrm{LiCoO}}_2$ values for ${\mu }_{\mathrm{Li}}$ are solid vertical lines, and the boundaries for thermodynamic stability of LiPON are dashed lines.

Figure 3

Schematic of the electrostatic potential and valence bands at the interfaces between LiPON and ${\mathrm{Li}}_x{\mathrm{CoO}}_2$ for (a) $x=1$ and (b) $x=0.5$. Electron transfer based on the band structure and ${\mathrm{Li}}^{+}$ transfer based on defect formation energies are illustrated schematically. The shapes of the curves are for illustrative purposes only. Computed bulk offsets $\mathrm{\Delta }{E}_B$, intrinsic offsets $\mathrm{\Delta }{E}_I$, and resulting potential shift $e\mathrm{\Delta }\varphi$ are indicated.

Figure 4

Thermodynamic potentials and band edges in a model 1D $\mathrm{Li}/\mathrm{LiPON}/{\mathrm{Li}}_x{\mathrm{CoO}}_2$ battery in open circuit conditions. (a) Discharged state ($x=1$). (b) Charged state ($x=0.5$)