Unravelling Charge Carrier Mobility in d₀‐Metal‐based Spinels

Abstract

Enabling high Mg ion mobility, spinel-type materials are promising candidates for cathode or solid electrolyte applications. To elucidate the factors governing the observed high mobility of multivalent ions, periodic DFT calculations of various charge carriers (A = Li, Na, K, Mg, Ca, Zn and Al) in the ASc 2 S 4 and ASc 2 Se 4 spinel compounds were performed, resulting in the identification of a Brønsted-Evans-Polanyi-type scaling relation for the migration barriers of the various charge carriers. Combining this scaling relation with the derivation of a descriptor, solely based on easily accessible observables, constitutes a conceptual framework to investigate ion mobility in d 0 -metal-based spinel chalcogenides with significantly reduced computational effort. This approach was exemplarily verified for various d 0 -metal-based spinel chalcogenide compounds AB 2 X 4 (B = Sc, Y, Ga, In, Er and Tm; X = O, S and Se) and led to the identification of d 0 -metal-based CaB 2 O 4 spinels as promising compounds possibly enabling high Ca ion mobility.

Ion Mobility in Crystalline Battery Materials

“…The discovery of the defect formation energy as a significant feature for interstitial migration is noteworthy as it reflects a kind of Brønsted-Evans-Polanyi-type relation between activation energies and site preference of the charge carriers. [4] Overall, these analyses will aid in designing efficient electrodes and solid electrolytes by narrowing down the essential properties in a multidimensional design space. However, to extend the results beyond anti-perovskites, further research is necessary, such as incorporating dynamic phenomena like lattice vibrations and poly-anion rotations into the feature set.…”

“…Such improvements are evident in the low migration barriers of Ca in d 0 ‐metal oxide spinels. [ 4 ] Migration barriers in spinel materials have recently been used to derive a descriptor for the ion mobility based on ionic radii, oxidation states, and electronegativities, as mentioned in the previous section. [ 3 ] Additionally, it was shown that transport properties of spinel compounds are impacted by transition metal cations, discovering that these metals have a notable impact on the barriers for Mg 2+ migration in such compounds.…”

“…The discovery of the defect formation energy as a significant feature for interstitial migration is noteworthy as it reflects a kind of Brønsted–Evans–Polanyi‐type relation between activation energies and site preference of the charge carriers. [ 4 ]…”

“…In recent years, significant progress has been made in our conceptual understanding of ion mobility in crystalline electrode materials, especially concerning the role of non-ionic interaction between the migrating ion and the host lattice. [2][3][4][5] In this review, we will discuss the materials' properties that correlate with ionic conductivity, in particular with the height of the activation barrier, using the descriptor concept. Both experimental and theoretical studies will be addressed in order to establish strategies to identify solid electrolytes and electrodes with improved mobility.…”

To Be or Not to Be – Is MgSc2Se4 a Mg‐Ion Solid Electrolyte?

“…This high electronic conductivity poses a challenge for its practical application as it leads to significant self-discharge. [16] In our earlier work, we estimated the self-discharge for a charged Mg|MgSc 2 Se 4 |Mo 6 S 8 battery and found that 10% of the total charge capacity would be lost within a short duration of 16 h. [18] Due to the promising ionic conductivity of MgSc 2 Se 4 reported by Canepa et al, follow-up works have been carried out to gain a more comprehensive understanding. Wang et al employed two routes of compositional tuning to suppress the electronic conductivity of MgSc 2 Se 4 , but neither method was successful.…”