# Fileset

[76_Sodeyama&Kaneko_Electrochemistry 2024_Ether decomposition on MgM2O4 spinel surface.pdf](https://mdr.nims.go.jp/filesets/699cb16b-d859-4409-be41-a37ee98dd4c4/download)

## Creator

[Tomoaki KANEKO](https://orcid.org/0000-0002-5296-7403), [Yui FUJIHARA](https://orcid.org/0000-0002-4842-5740), [Toshihiko MANDAI](https://orcid.org/0000-0002-2403-7794), [Hiroaki KOBAYASHI](https://orcid.org/0000-0001-6705-9515), [Keitaro SODEYAMA](https://orcid.org/0000-0002-9228-0729)

## Rights

[Creative Commons BY Attribution 4.0 International](https://creativecommons.org/licenses/by/4.0/)

## Other metadata

[Ether Molecule Decomposition on Mg<i>M</i><sub>2</sub>O<sub>4</sub> (<i>M</i> = Mn, Fe, Co) Spinel Surface: A First-principles Study](https://mdr.nims.go.jp/datasets/14ff370e-ef52-4598-b020-cf8ed917202e)

## Fulltext

untitledArticle Electrochemistry, 92(2), 027003 (2024)Ether Molecule Decomposition on MgM2O4 (M = Mn, Fe, Co) Spinel Surface:A First-principles StudyTomoaki KANEKO,a,e,* Yui FUJIHARA,b,§ Toshihiko MANDAI,c,§Hiroaki KOBAYASHI,d,§ and Keitaro SODEYAMAe,*a Department of Computational Science and Technology, Research Organization for Information Science and Technology,1-18-16 Hamamatsucho, Minato, Tokyo 105-0013, Japanb Energy Transformation Research Laboratory, Central Research Institute of Electric Power Industry,2-6-1 Nagasaka, Yokosuka 240-0196, Japanc Center for Advanced Battery Collaboration, Center for Green Research on Energy and Environmental Materials,National Institute for Materials Science (NIMS), 1-1 Namiki, Tsukuba 305-0044, Japand Department of Chemistry, Faculty of Science, Hokkaido University, Kita 10, Nishi 8, Kita-ku, Sapporo 060-0810, Japane Data-driven Materials Research Field, Center for Basic Research on Materials, National Institute for Materials Science (NIMS),1-1 Namiki, Tsukuba 305-0044, Japan* Corresponding authors: kaneko.tomoaki@rist.or.jp (T. K.), SODEYAMA.Keitaro@nims.go.jp (K. S.)ABSTRACTThe transition between MgM2O4 (M = Mn, Fe, Co) spinels (SPs) and MgMO2 rock salts (RS) has attracted considerable interest for cathodereactions in future magnesium battery applications. To improve the cycling performance, one should suppress the consumption of solventmolecules. In this study, we investigated ether solvent decomposition on MgM2O4 SP and MgMO2 RS surfaces using first-principlescalculations. We found that the C–H bond dissociation of ether molecules on the SP surface was exothermic, while the C–H bonddissociation on RS and C–O bond dissociation on both SP and RS surfaces were endothermic, irrespective of the transition metal element.The products of C–H dissociation reactions at the SP surfaces have occupied states originating from SP surfaces inside the bandgap. As theSP surface is destabilized by C–H dissociation, the electrons at this level can be extracted as an oxidative current.© The Author(s) 2023. Published by ECSJ. This is an open access article distributed under the terms of the Creative Commons Attribution 4.0 License (CC BY,http://creativecommons.org/licenses/by/4.0/), which permits unrestricted reuse of the work in any medium provided the original work is properly cited. [DOI:10.5796/electrochemistry.23-00087].Keywords : First-principles Calculations, Mg-battery, Solvent Decomposition, Mg-spinel1. IntroductionThe demand for rechargeable batteries with high energy densitieshas increased because of the widespread use of portable electronicdevices and vehicles. Mg batteries have attracted significant interestfor their future high rechargeability1 because of the high specificcapacity of magnesium metal anodes (2200mAhg¹1) compared tothe graphite anodes (370mAhg¹1) used in conventional lithium-ionbatteries. MgM2O4 (M =Mn, Fe, Co)-based spinels (SP) areconsidered promising candidates for use as cathode materials inmagnesium batteries. During the discharging process, the SPtransforms into the MgMO2 rock salt (RS) phase:MgM2O4 þMg2þ þ 2e� � 2MgMO2: ð1ÞAlthough Mg batteries with an SP cathode exhibit a high potential(2–3V vs. Mg2+/Mg) and high capacities (260–270mAhg¹1), poorreversibility and slow kinetics are critical problems for practicalapplications.1,2 The consumption of solvent or anion moleculesduring cycling is considered a critical problem in the cycleperformance. The purpose of this study was to discuss and gainfurther insight into the decomposition of solvent molecules atcathode surfaces using first-principles calculations.For Mg batteries with SP cathodes, the oxidative decompositionof the solvent is an important issue for practical applications.Owing to the undesired decomposition of electrolytes at thecathode–electrolyte interface during charging, the deliverablecapacity decreases drastically upon cycling. The adsorption andsubsequent decomposition of ether at the [cathode « electrolyte]interface would impede intercalation/deintercalation of Mg2+ into/from the cathode due to the large diffusion barrier of decom-position products generated at the interface. This undesired sidereaction can consequently lead to continuous decrease of thedeliverable capacities with cycling. To address these critical issues,certain inorganic and organic ionic liquid-based electrolytes havebeen developed and applied to Mg batteries; however, theseoxidatively stable electrolytes are less compatible with Mg metalanodes.3,4Recently, the oxidation potentials of ether solvent decompositionfor MgM2O4 in Mg batteries were determined experimentally andcomputationally.5,6 Han et al. observed the oxidation decompositionof ether-based electrolytes on SP cathodes at a lower oxidationpotential than their potential anodic limits and suggested the specificcatalytic activity of SP cathodes against ether solvents.5,6 They alsoreported the highest oxidation potential of ether solvents whenMgFe2O4 was used as a cathode.5,6 The origin of such transition-element-dependent oxidation potentials of ether solvents can beexplained by the electronic structures of the SP cathode anddifferences in the HOMO energy levels between the solvent ethersand SP cathode surfaces. However, the detailed decompositionmechanism and the decomposition behavior on RS cathodes remainunclear.§ECSJ Active MemberT. Kaneko orcid.org/0000-0002-5296-7403Y. Fujihara orcid.org/0000-0002-4842-5740T. Mandai orcid.org/0000-0002-2403-7794H. Kobayashi orcid.org/0000-0001-6705-9515K. Sodeyama orcid.org/0000-0002-9228-0729ElectrochemistryThe Electrochemical Society of Japan https://doi.org/10.5796/electrochemistry.23-00087https://doi.org/10.50892/data.electrochemistry.24980718Received: September 6, 2023Accepted: December 28, 2023Published online: January 12, 2024Issued: February 15, 20241https://orcid.org/0000-0002-5296-7403https://orcid.org/0000-0002-4842-5740https://orcid.org/0000-0002-2403-7794https://orcid.org/0000-0001-6705-9515https://orcid.org/0000-0002-9228-0729http://creativecommons.org/licenses/by/4.0/https://doi.org/10.5796/electrochemistry.23-00087http://creativecommons.org/licenses/by/4.0/http://creativecommons.org/licenses/by/4.0/https://orcid.org/0000-0002-5296-7403https://orcid.org/0000-0002-5296-7403https://orcid.org/0000-0002-5296-7403https://orcid.org/0000-0002-4842-5740https://orcid.org/0000-0002-4842-5740https://orcid.org/0000-0002-4842-5740https://orcid.org/0000-0002-2403-7794https://orcid.org/0000-0002-2403-7794https://orcid.org/0000-0002-2403-7794https://orcid.org/0000-0001-6705-9515https://orcid.org/0000-0001-6705-9515https://orcid.org/0000-0001-6705-9515https://orcid.org/0000-0002-9228-0729https://orcid.org/0000-0002-9228-0729https://orcid.org/0000-0002-9228-0729https://doi.org/10.5796/electrochemistry.23-00087https://doi.org/10.5796/electrochemistry.23-00087https://doi.org/10.50892/data.electrochemistry.24980718https://doi.org/10.50892/data.electrochemistry.24980718In contrast, theoretical studies on solvent decomposition on thecathode surfaces of the Mg battery is limited. Han et al. discussedthe origin of oxidative decomposition by the electronic structures ofthe SP surfaces.5,6 For the cathode materials of Li-ion batteries,solvent molecule decomposition on the cathode surface has beenintensively investigated by several authors.7–29 However, moststudies have been conducted on ethylene carbonate (EC) and relatedcarbonate molecules, such as fluoroethylene carbonate and diethylcarbonate, while only quite recent report handles the decompositionof ether molecules.29 Another quite recent work by Zhou et al.reports the decomposition of 1,2-dimethoxyethane on the SP surfaceand the decomposition reaction on SP surface is mainly determinedby the catalytic chemistry of SP surface.30 Therefore, the under-standing of oxidative decomposition at the SP surface is still limited.In this study, we performed first-principles calculations toinvestigate the origin of oxidative decomposition at the cathodesof Mg batteries.2. Computational DetailsIn this study, we employed the quantum espresso code,34 which isa first-principles calculation code based on density functional theorywith a plane-wave basis set. The generalized gradient approximation(GGA)35 and ultrasoft pseudopotentials were used.36,37 In ourcalculations, the semicore states of 2s and 2p orbitals of Mg and 3sand 3p orbitals of Mn, Fe, and Co were treated as valence electrons.The DFT-D3 dispersion correction was considered.38 For d-orbitalsof Mn, Fe, and Co, an isotropic model of DFT+U was adopted.39The Ueff values were 5.0, 5.0, and 6.0 eV for Mn, Fe, and Co,respectively, which are typical values, as discussed in our previouspaper.40 The cutoff energies of the plane-wave basis set and thecharge density were selected to be 35 and 315Ry, respectively. Forthe calculations of primitive cells, we used a special k-samplingof 2 © 2 © 2. The lattice constants of MgFe2O4 (SP-MFO) andMgCo2O4 (SP-MCO) were determined by minimizing the totalenergy. To optimize the lattice constant of SP MgMn2O4 (SP-MMO)using a stress tensor, cutoff energies of the plane wave basis set andcharge densities of 55 and 495Ry, respectively, were employedbecause SP-MMO belongs to the tetragonal lattice system owing tothe strong Jahn-Teller effect in Mn3+. We assumed antiferromagneticordering along the [110] direction, alternating between spins up anddown.41 For SP-MCO, a low-spin state is adopted for Co3+ becauseit is more stable than the high-spin state.The RS phases of MgMnO2 (RS-MMO), MgFeO2 (RS-MFO),and MgCoO2 (RS-MCO) are also calculated. For simplicity, weassumed that the transition metal atoms reside at the same site in SPand that the Mg atoms occupy the 16c site of the RS phase. Assummarized in Table 1, the optimized lattice constants agree wellwith the experimental values, except for a few % changes. Then, thevoltage of with Mg metal anode is defined asVMg=Mg2þ ¼ � 12e½2EMgMO2� EMgM2O4� EMg�; ð2Þwhere EMgMO2, EMgM2O4, EMg are the total energies per formula unitsfor SP, RS, and Mg in hcp lattice, respectively. The obtainedVMg=Mg2þ values were 2.20 for Mn, 1.86 for Fe, and 2.75 for Co.These results agree well with the experimental results reported inRef. 3, i.e., 2.3 for Mn, 2.2 for Fe, and 2.9 for Co, and our previouscalculations without vdW correction.40We considered the (001) cleaved slab models of SP and RSsurfaces, with the thickness of the slab model as a single primitivesize. For the SP surface, we used the RS-like reconstruction surfacemodel previously reported in Ref. 40. The surface slab models arecharge neutral. For surface calculations, we used special k-samplingof 2 © 2 © 1. To remove the spurious interactions between periodicimages, an effective screening medium was employed42 with avacuum layer thicker than 10¡ on both sides of the slab. For theprojected density of states (PDOS) calculations, we used ¥ pointcentered 4 © 4 © 1 k-sampling.In the experiments, glyme molecules such as tri-glyme (G3) andtetra-glyme (G4) were used as solvents. However, such glymemolecules are excessively long to simulate, that is, their adsorptionstructures are complicated, and the number of possible reactionsincreases dramatically. As mentioned in the Introduction, thereare only a few reports of theoretical studies on ether moleculedecomposition on the surface of the cathode of Mg batteries.Therefore, we consider the simplest ether molecule, dimethylether(Me2O), in the primary stage of this study. We define the adsorptionenergy (Eads) as follows:Eads ¼ Esurf+ads � Esurf � Emol; ð3Þwhere Esurf+ads, Esurf, and Emol denote the total energies of the surfacewith the adsorbate, surface, and Me2O molecules, respectively.Bader charge analysis was performed using bader code.43–46 Theresults of the Bader charge are summarized in the SupportingInformation.The O atoms in Me2O were placed at the Mg andM (Mn, Fe, Co)atom sites on the SP or RS surfaces. We consider the followingreactions, referred to as cut-1 and cut-2:Me2O ! CH3Oþ CH3 ðcut-1Þ; ð4ÞandMe2O ! CH3OCH2 þ H ðcut-2Þ: ð5ÞThe CH3 radial and H ions were placed on the surface of O atoms.Hereafter, the oxygen atom of Me2O is referred to as OMe2O. Thenotations OMe2O@Mg and OMe2O@M represent the adsorption siteson OMe2O. We define the reaction energy by the change in theadsorption energy. In this paper, we neglected the solvation effect ofthe molecule. The adsorption energy may change by considering thesolvation effect. On the other hand, the effect of solvation on thereaction energy would be much smaller than that of adsorptionenergy, since the reactant and product are adsorbed on the surfaces.3. Results and DiscussionFirst, we discuss the structural properties and energetics of Me2Odecomposition. The calculated adsorption energies are summarizedin Table 2. In this table, OMe2O@Mg and OMe2O@M denote theadsorption sites of Me2O. In Fig. 1a, ball-stick models of adsorbateson SP-MCO for the O@M case are shown. The other results aresummarized in the Supporting Information.For the SP surfaces, Me2O was preferentially adsorbed at the Mgsite for SP-MMO, whereas it was preferentially adsorbed at thetransition metal site for SP-MFO and SP-MCO. The calculatedMg–O and M–O interatomic distances for Me2O adsorption areTable 1. Results of bulk materials.Mn Fe CoaSP, cSP (¡) 8.227, 9.575 8.576 8.166Exp. 8.099, 9.284a 8.397b 8.138cDiff. 1.5%, 3.1% 2.1% 3.4%aRS (¡) 8.798 8.660 8.567Exp. 8.672d 8.503cDiff. 1.5% 7.5%VMg=Mg2þ (V) 2.20 1.86 2.75Exp. 2.3c 2.2c 2.9ca: Ref. 31, b: Ref. 32, c: Ref. 3, d: Ref. 33.Electrochemistry, 92(2), 027003 (2024)2summarized in the Supporting Information. The different trends inthe adsorption sites on SP-MMO from SP-MFO or SP-MCO arecaused by the strong Jahn–Teller effect in SP-MMO, that is, the Mn–O interatomic distance is much longer than that in SP-MFO or SP-MCO. Such an electronic configuration of the surface Mn ion playsan important role in the energetics of adsorbates.However, for the adsorbates of Cut-1 and Cut-2, the adsorptionenergies for OMe2O@M were lower than those for OMe2O@Mg. Inthe Cut-1 structure, the H atom in the methyl group forms ahydrogen bond with the O in Me2O for SP-MCO. We observed thesame trend for the other transition metal elements, as shown in theSupporting Information. In the Cut-2 structure, the dangling bond atthe C atom was passivated by the topmost O atom of SP-MCO. Asshown in the Supporting Information, this behavior is the sameas that of other M elements, except for SP-MMO, OMe2O, and M.Interestingly, the adsorbate was stabilized by disconnecting the bondbetween OMe2O and M in Cut-2 at OMe2O@M of SP-MMO case.We also performed a Bader charge analysis, and the results areprovided in the Supporting Information. The number of valenceelectrons in Me2O was 20. The total Bader charge of Me2O wasunchanged for pristine Me2O and for the cut-1 reaction. However,the total Bader charge associated with adsorbate atoms decreases(18.17–18.70) by the cut-2 reaction. The Bader charge of the H atomfor Cut-2 is summarized in the Supporting Information. Because theBader charge of the surface H atom is much smaller than unity,the Cut-2 reaction can be understood as deprotonation instead ofdehydrogenation.Next, we consider the RS surface. For RS surfaces, Me2Opreferentially adsorbs at the Mg site, irrespective of the transitionmetal element. The adsorption energies become smaller for Cut-1and OMe2O@M than for OMe2O@Mg, whereas the adsorptionenergies decrease to only a few tens meV difference for Cut-2. InFig. 2a, ball-stick models of adsorbates on RS-MCO for O@Mcases are shown. The results for the others are provided in theSupporting Information. The characteristics on structures of theMe2O adsorption and Cut-1 are similar to those of the SP-surfacecases. For Me2O adsorption, the difference in the interatomicdistances between OMe2O and the adsorption sites is much smallerTable 2. Me2O adsorption energy (Eads) on the SP and RS surfaces.SP-MMO SP-MFO SP-MCO RS-MMO RS-MFO RS-MCOMe2O, OMe2O@Mg ¹0.691 ¹0.745 ¹0.868 ¹0.647 ¹0.695 ¹0.657Me2O, OMe2O@M ¹0.463 ¹0.814 ¹1.297 ¹0.528 ¹0.609 ¹0.514cut-1, OMe2O@Mg +0.664 +0.543 +0.331 +0.427 +0.538 +0.544cut-1, OMe2O@M +0.270 ¹0.649 ¹0.041 +0.340 +0.330 +0.408cut-2, OMe2O@Mg ¹1.233 ¹1.731 ¹2.182 +0.535 +0.720 +0.522cut-2, OMe2O@M ¹1.357 ¹2.009 ¹3.942 +0.578 +0.695 +0.585Figure 1. (a) Optimized structures of (i) pristine Me2O, (ii) cut-1, and (iii) cut-2 for SP-MCO and OMe2O@Mg. (b) Local density of states of(i) pristine Me2O, (ii) cut-1, and (iii) cut-2 for SP-MCO and OMe2O@Mg. (c) PDOS of (i) pristine Me2O, (ii) cut-1, and (iii) cut-2 for SP-MCOand OMe2O@Mg.Electrochemistry, 92(2), 027003 (2024)3than that in the SP-MMO case because of the absence of a strongJahn–Teller effect. For Cut-2, the dangling bond at the C atom waspassivated by the surface transition metal atom, whereas thedangling bond was passivated by the O atom on the SP surface.For the Bader charge of the RS case, the total Bader charge wasclose to that of the isolated Me2O molecule. However, the totalBader charge for cut-2 was much closer to that of the isolated Me2Omolecule. Because the Bader charge of the surface H is muchsmaller than that of the isolated molecule, the cut-2 reaction isdeprotonation instead of dehydrogenation, similar to the SP-surfacecase. Then, an excess of electrons accumulated at the C atoms,which were connected to the surface H atoms (see Table S5).Consequently, the C atoms were anionic and passivated by thesurface M atoms on the RS surface, whereas the C atoms werepassivated by surface O on the SP surface. The M3+ ions receive anelectron from a molecule on the SP surface, whereas the M2+ ionsare difficult to reduce.Next, we discuss the energies of the decomposition reactions.The calculated reaction energies are listed in Table 3. Here, thereaction energy is defined as the difference in the total energy, thatis, the reaction is exothermic when the reaction energy is negative.For the SP surfaces, the reaction energy was negative for the Cut-2reaction, irrespective of the adsorption site and transition metal,whereas the reaction energy of the Cut-1 reaction was positive.Because the reaction energy of the Cut-2 reaction becomessignificantly more negative for OMe2O@M than for OMe2O@Mg,the Cut-2 reaction should occur at theM site. For the RS surfaces, onthe other hand, the reaction energies are positive for both Cut-1 andCut-2 reactions, that is, the reactions are endothermic.We briefly mention the use of DFT+U calculations in the ResultsSection. The parameter U is used to enlarge the electroniccorrelation at the 3d-orbital, which is underestimated in DFT andGGA. The bandgap of transition metal oxides can be improvedusing appropriate U values. As mentioned in our previous study, thecalculated VMg=Mg2þ depends on Ueff. A quantitative comparison ofthe results, such as the reaction energies, between different SPsmight be difficult. Therefore, we will not discuss a comparison ofthe transition metal element differences.The decomposition of solvent molecules on cathode surfaces hasbeen investigated by several researchers.7–28 Most calculationsFigure 2. (a) Optimized structures of (i) pristine Me2O, (ii) cut-1, and (iii) cut-2 for RS-MCO and OMe2O@Mg. (b) Local density of states of(i) pristine Me2O, (ii) cut-1, and (iii) cut-2 for RS-MCO and OMe2O@Mg. (c) PDOS of (i) pristine Me2O, (ii) cut-1, and (iii) cut-2 for RS-MCO and OMe2O@Mg.Table 3. Reaction energy of Me2O decomposition on SP and RS.SP-MMO SP-MFO SP-MCO RS-MMO RS-MFO RS-MCOcut-1, OMe2O@Mg +1.354 +1.288 +1.199 +1.074 +1.233 +1.200cut-1, OMe2O@M +0.732 +0.165 +1.256 +0.868 +0.939 +0.922cut-2, OMe2O@Mg ¹0.543 ¹0.986 ¹1.315 +1.181 +1.415 +1.179cut-2, OMe2O@M ¹0.894 ¹1.195 ¹2.645 +1.111 +1.304 +1.099Electrochemistry, 92(2), 027003 (2024)4consider the ring-opening reactions of EC at the surface of thecathode materials of Li-ion batteries. Leung performed DFT-MDsimulations of EC adsorbed onto a partially delithiated SPLi0.6Mn2O4 surface.7,10 The ring-opening reaction of EC and protontransfer from the product of the ring-opening reaction to the surfacewere observed. Proton transfer is a two-electron oxidative reactiontriggered by the preceding ring-opening reaction. For the ECdecomposition on SP Li0.67Mn2O4(111) surface, in contrast, thedeprotonation occurs before the ring-opening reaction. In this case,the decomposition reaction is exothermic, whereas deprotonation isendothermic. Therefore, the results seem to be sensitive to thesurface orientation.Giordano et al. reported C–H bond dissociation of EC on layeredtype LixMO2ð10�14Þ and MO(100) surfaces.24,27 They showed thatthe C–H bond dissociation is exothermic for LixMO2ð10�14Þ, whereasthe reactions become endothermic for MO(100). Our results are ingood agreement with these results, although the cathode materialand solvent molecules are different. Okuno et al. reported thedecomposition of EC on LiNi0.5Mn1.5O4 surface.11 They found thatthe C–H dissociation reaction of pristine EC on partially delithiatedLiNi0.5Mn1.5O4 is sensitive to the H adsorption site of O, that is, thereaction is exothermic for a two-coordinated surface O andendothermic for a three-coordinated surface O. In our study, therewere no two-coordinated surfaces O because we used a recon-structed surface. Therefore, the Cut-2 reaction becomes moreexothermic when the SP surface is partially demagnethiated SP.Next, we discuss electronic structures. The calculated PDOS ofSP-MCO and RS-MCO with OMe2O@Mg are shown in Figs. 1c and2c, respectively. In Figs. 1c and 2c, the up- and down-spincomponents of PDOS are presented in the top and bottom halvesof each panel, respectively. The upward and downward arrowsrepresent the up- and down-spin components of the highest occupiedlevel in the solvent, respectively. In these figures, the energy wasmeasured using Fermi energy. The results for the other SP and RSare summarized in the Supporting Information.For SP-MCO surfaces, the HOMO level of Me2O is 2.03 eVbelow the valence band top of SP-MCO as shown in Fig. 2b–(i).The positions of the HOMO levels of Me2O measured from SP andRS surfaces are summarized in the Supporting Information. Therange of the HOMO level position, measured from the top of thesurface valence band, was 1.4–2.0 eV. For the Cut-1 model, theadsorbate levels appeared in the gap of SP-MCO as shown inFig. 1c–(ii). This behavior was also observed for the other SPsurfaces. In contrast, for the Cut-2 model, the levels originating fromSP-MCO can be found in the gap of SP-MCO, and the HOMOlevels of adsorbates are located outside the SP-MCO gap. This resultis consistent with the decrease in the total Bader charge of Me2O forthe Cut-2 on SP. Notably, these trends are the same irrespective ofthe transition metal element and the adsorption site of OMe2O.For the RS-MCO surface, the HOMO is 1.89 eV below thevalence band top of RS-MCO. The range of HOMO levels measuredfrom the valence band top is 1.9–2.7 eV, suggesting that theadsorbates are harder to oxidize compared with SP surfaces. Forboth the Cut-1 and Cut-2 models, adsorbate-related levels wereobserved inside the bandgap of RS-MCO. For the other RS surfaces,such adsorbate-related levels appeared inside the band gap or at theenergetically similar position of the top of the valence band for Cut-1 and Cut-2, as summarized in the Supporting Information.Next, we considered the mechanism of oxidative solventdecomposition at the cathode surface. Because the Cut-2 reactionson SP surfaces are exothermic irrespective ofM element, we focusedon the Cut-2 reaction, which is a unique candidate for oxidativedecomposition. As discussed, the occupied states originating fromSP surfaces appear just above the top of the valence band for theCut-2 reaction, owing to the charge transfer from the adsorbate toSP. Notably, these occupied states are easier to oxidize than otherstates on the SP surface, which could be the origin of the oxidativecurrent. Electrons and Mg ions were extracted from the cathode foroxidative decomposition at the cathode surface. Therefore, thepartially demagnethiated SP surfaces are more likely to undergodecomposition.Giordano et al. reported that the decomposition reaction becomesenergetically favorable on the oxide surface with the transition metalelement from left to right in the periodic table.24,27 Although we canobserve similar trends for the Cut-2 reaction, these results aresensitive to the magnitude of U parameters. If we are to make suchconclusions, we need to check the U dependence of the reactionenergy, which is beyond the scope of the present study. Giordanoet al. also reported that the decomposition reaction becomesenergetically favorable by increasing transition metal valence inthe oxide, where a higher degree of EC dissociation was found asthe Fermi level was lowered into the oxide O 2p band.Next, we discuss the correspondence between the results,experiments, and other theories. Quite recently, Han et al. examinedthe oxidation potentials (Eox) of the cyclic voltammograms of Mgbatteries.6 In their experiments, 0.5mol dm¹3 [Mg(G4)][TFSA]2/[Pry1,3][TFSA] electrolytes at 100 °C were employed, where TFSAand Pry1,3 denote bis(trifluoromethanesulfonyl)amide and N-methyl-N-propylpyrrolidinium, respectively. The obtained Eox are3.05, 3.33, and 3.20 eV for SP-MMO, SP-MFO, and SP-MCO,respectively, that is, the oxidative decomposition is much suppressedfor the SP-MFO cathode.6To understand the experimental results, the electronic structuresof the pristine MgM2O4(100) (M =Mn, Fe, Co) surfaces wereinvestigated.6 In their discussion, the position of the top of thevalence band of SP oxide measured from the vacuum level wasused. The obtained levels of the valence band top were ¹4.92,¹5.32, and ¹4.73 eV for SP-MMO, SP-MFO, and SP-MCO,respectively. They discussed how the oxidative decomposition of thesolvent occurs when the HOMO of the solvent exceeds the top ofthe valence band. This discussion also explained the experimentalresults on the order of the oxidative decomposition reaction.However, our calculated results did not support their interpretationof the experiments. As discussed, the HOMO level of the solventshould be lower than that at the top of the valence band.Quite recently, Zhou et al. reported that theoretical simulationson the 1,2-dimethoxyethane (DME) decomposition on Mg-SPsurface.30 They considered the C–O bond dissociation of DMEand concluded that the decomposition reaction is mainly catalyticchemistry rather than the oxidative decomposition. They alsoperformed the decomposition calculations on the Mg-extracted SPsurfaces. According to several experiments for Mg-SP, the RSphases are formed on the Mg-SP surface,33,47 indicating that theMg deficient SP surface is hard to be realized. Moreover, thedecompositions are endothermic even on the Mg-deficient SPsurfaces. On the other hand, we also explained the Cut-2 reactionson RS are endothermic. For the SP surfaces covered by RS phases,however, there are M3+ ions in the bulk region of SP, which can bereduced by the Cut-2 reaction. We can expect that the Cut-2reactions on the SP surfaces covered by the RS phase can proceed,if the SP phases are not perfectly transformed into RS phases.Therefore, the observed reactions by Han et al. are presumed to bethe Cut-2 reaction.4. SummaryIn this study, we investigated the ether solvent decomposition onMgM2O4 (M =Mn, Fe, Co) SP and MgMO2 (M =Mn, Fe, Co) RSsurfaces using first-principles calculations. The energetics andchanges in the electronic structures of the C–O and C–H bonddissociations on both SP spinel and rock-salt surfaces wereexamined. We found that the C–H bond dissociation of etherElectrochemistry, 92(2), 027003 (2024)5molecules on the spinel surface was exothermic, irrespective of thetransition metal element, whereas other reactions were endothermic.The calculated PDOS for pristine molecule adsorption shows thatdirect oxidation of the adsorbate is not feasible. The productsresulting from the C–H dissociation reactions at the spinel surfacesoccupied states originating from the SP surfaces within the bandgap.Because the hydrogen atom behaves as a proton, as revealed bythe Bader charge analysis, the spinel oxide surface is effectivelyreduced, and the corresponding states can be observed inside theband gap in the PDOS. The appearance of occupied states inside thebandgap indicates that the oxidized states should be stabilized. Asthe spinel surface is destabilized by C–H dissociation, the electronsat this level can be extracted as an oxidative current.AcknowledgmentsThe authors thank Dr. Yoshitaka Tateyama and Dr. TomonobuNakayama for their fruitful discussions. The calculations wereperformed using the Numerical Materials Simulator at NIMS andthe ITO supercomputer at the Research Institute for InformationTechnology, Kyushu University. This study was partially supportedby JST ALCA-SPRING Grant No. JPMJAL1301, Japan.CRediT Authorship Contribution StatementTomoaki Kaneko: Conceptualization (Equal), Formal analysis (Lead), Investigation(Lead), Writing – original draft (Lead)Yui Fujihara: Formal analysis (Supporting), Investigation (Supporting), Resources(Lead)Toshihiko Mandai: Supervision (Supporting), Writing – original draft (Supporting)Hiroaki Kobayashi: Conceptualization (Equal), Project administration (Equal),Supervision (Equal)Keitaro Sodeyama: Conceptualization (Lead), Project administration (Lead),Supervision (Lead)Data Availability StatementThe data that support the findings of this study are openly available under the termsof the designated Creative Commons License in J-STAGE Data listed in D1 ofReferences.Conflict of InterestThe authors declare no conflict of interest in the manuscript.FundingJapan Science and Technology Agency: JPMJAL1301ReferencesD1. T. Kaneko, Y. Fujihara, T. Mandai, H. Kobayashi, and K. Sodeyama, J-STAGEData, https://doi.org/10.50892/data.electrochemistry.24980718, (2024).1. K. Shimokawa and T. Ichitsubo, Curr. Opin. Electrochem., 21, 93 (2020).2. I. D. Johnson, B. J. Ingram, and J. Cabana, ACS Energy Lett., 6, 1892 (2021).3. S. Okamoto, T. Ichitsubo, T. Kawaguchi, Y. Kumagai, F. Oba, S. Yagi, K.Shimokawa, N. Goto, T. Doi, and E. Matsubara, Adv. Sci., 2, 1500072 (2015).4. T. Mandai, K. Tatesaka, K. Soh, H. Masu, A. Choudhary, Y. Tateyama, R. Ise, H.Imai, T. Takeguchi, and K. Kanamura, Phys. Chem. Chem. Phys., 21, 12100(2019).5. J. Han, S. Yagi, and T. Ichitsubo, J. Power Sources, 435, 226822 (2019).6. J. Han, S. Yagi, H. Takeuchi, M. Nakayama, and T. Ichitsubo, J. Mater. Chem. A,9, 26401 (2021).7. K. Leung, J. Phys. Chem. C, 116, 9852 (2012).8. N. Kumar, K. Leung, and D. J. Siegel, J. Electrochem. Soc., 161, E3059 (2014).9. K. Leung, Chem. Mater., 29, 2550 (2017).10. K. Leung, Rosy, and M. Noked, J. Chem. Phys., 151, 234713 (2019).11. Y. Okuno, K. Ushirogata, K. Sodeyama, G. Shukri, and Y. Tateyama, J. Phys.Chem. C, 123, 2267 (2019).12. J. L. Tebbe, T. F. Fuerst, and C. B. Musgrave, ACS Appl. Mater. Interfaces, 8,26664 (2016).13. S. Xu, G. Luo, R. Jacobs, S. Fang, M. K. Mahanthappa, R. J. Hamers, and D.Morgan, ACS Appl. Mater. Interfaces, 9, 20545 (2017).14. Y. Yu, P. Karayaylali, Y. Katayama, L. Giordano, M. Gauthier, F. Maglia, R. Jung,I. Lund, and Y. Shao-Horn, J. Phys. Chem. C, 122, 27368 (2018).15. X. Qin, P. B. Balbuena, and M. Shao, J. Phys. Chem. C, 123, 14449 (2019).16. M. Lin, X. Yang, X. Zheng, J. Zheng, J. Cheng, and Y. Yang, J. Electrochem. Soc.,168, 050505 (2021).17. G. Shukri, B. Rendy, A. G. Saputro, F. V. Panjaitan, P. S. Tarabunga, M. K.Agusta, N. N. Mobarak, and H. K. Dipojono, J. Phys. Chem. C, 126, 2151 (2022).18. M. R. Fuhst and D. J. Siegel, J. Phys. Chem. C, 124, 24097 (2020).19. X. Sun, R. Xiao, X. Yu, and H. Li, Langmuir, 37, 5252 (2021).20. Q. Chen, Y. Pei, H. Chen, Y. Song, L. Zhen, C.-Y. Xu, P. Xiao, and G. Henkelman,Nat. Commun., 11, 3411 (2020).21. A. Bhandari, J. Bhattacharya, and R. G. S. Pala, J. Phys. Chem. C, 124, 9170(2020).22. R. Tatara, Y. Yu, P. Karayaylali, A. K. Chan, Y. Zhang, R. Jung, F. Maglia, L.Giordano, and Y. Shao-Horn, ACS Appl. Mater. Interfaces, 11, 34973 (2019).23. T. M. Østergaard, L. Giordano, I. E. Castelli, F. Maglia, B. K. Antonopoulos, Y.Shao-Horn, and J. Rossmeisl, J. Phys. Chem. C, 122, 10442 (2018).24. L. Giordano, P. Karayaylali, Y. Yu, Y. Katayama, F. Maglia, S. Lux, and Y. Shao-Horn, J. Phys. Chem. Lett., 8, 3881 (2017).25. M. Gauthier, P. Karayaylali, L. Giordano, S. Feng, S. F. Lux, F. Maglia, P. Lamp,and Y. Shao-Horn, J. Electrochem. Soc., 165, A1377 (2018).26. E. G. Leggesse, K.-H. Tsau, Y.-T. Liu, S. Nachimuthu, and J.-C. Jiang,Electrochim. Acta, 210, 61 (2016).27. L. Giordano, T. M. Østergaard, S. Muy, Y. Yu, N. Charles, S. Kim, Y. Zhang, F.Maglia, R. Jung, I. Lund, J. Rossmeisl, and Y. Shao-Horn, Chem. Mater., 31, 5464(2019).28. L. Huai, Z. Chen, and J. Li, ACS Appl. Mater. Interfaces, 9, 36377 (2017).29. K. Leung, Chem. Mater., 35, 2518 (2023).30. W. Zhou, C. Xu, B. Gao, M. Nakayama, S. Yagi, and Y. Tateyama, ACS EnergyLett., 8, 4113 (2023).31. Z. Feng, X. Chen, T. T. Fister, M. J. Bedzyk, and P. Fenter, J. Appl. Phys., 120,015307 (2016).32. S. M. Antao, I. Hassan, and J. B. Parise, Am. Mineral., 90, 219 (2005).33. Q. D. Truong, M. K. Devaraju, P. D. Tran, Y. Gambe, K. Nayuki, Y. Sasaki, and I.Honma, Chem. Mater., 29, 6245 (2017).34. P. Giannozzi, O. Andreussi, T. Brumme, O. Bunau, M. Buongiorno Nardelli, M.Calandra, R. Car, C. Cavazzoni, D. Ceresoli, M. Cococcioni, N. Colonna, I.Carnimeo, A. Dal Corso, S. de Gironcoli, P. Delugas, R. A. DiStasio, Jr., A.Ferretti, A. Floris, G. Fratesi, G. Fugallo, R. Gebauer, U. Gerstmann, F. Giustino,T. Gorni, J. Jia, M. Kawamura, H.-Y. Ko, A. Kokalj, E. Küçükbenli, M. Lazzeri,M. Marsili, N. Marzari, F. Mauri, N. L. Nguyen, H.-V. Nguyen, A.Otero de-la Roza, L. Paulatto, S. Poncé, D. Rocca, R. Sabatini, B. Santra, M.Schlipf, A. P. Seitsonen, A. Smogunov, I. Timrov, T. Thonhauser, P. Umari, N.Vast, X. Wu, and S. Baroni, J. Phys.: Condens. Matter, 29, 465901 (2017).35. J. P. Perdew, K. Burke, and M. Ernzerhof, Phys. Rev. Lett., 78, 1396 (1997).36. D. Vanderbilt, Phys. Rev. B, 41, 7892 (1990).37. K. F. Garrity, J. W. Bennett, K. M. Rabe, and D. Vanderbilt, Comput. Mater. Sci.,81, 446 (2014).38. S. Grimme, J. Antony, S. Ehrlich, and H. Krieg, J. Chem. Phys., 132, 154104(2010).39. M. Cococcioni and S. de Gironcoli, Phys. Rev. B, 71, 035105 (2005).40. T. Kaneko, Y. Fujihara, H. Kobayashi, and K. Sodeyama, Appl. Surf. Sci., 613,156065 (2023).41. W. Jin, G. Yin, Z. Wang, and Y. Q. Fu, Appl. Surf. Sci., 385, 72 (2016).42. M. Otani and O. Sugino, Phys. Rev. B, 73, 115407 (2006).43. G. Henkelman, A. Arnaldsson, and H. Jónsson, Comput. Mater. Sci., 36, 354(2006).44. W. Tang, E. Sanville, and G. Henkelman, J. Phys.: Condens. Matter, 21, 084204(2009).45. M. Yu and D. R. Trinkle, J. Chem. Phys., 134, 064111 (2011).46. E. Sanville, S. D. Kenny, R. Smith, and G. Henkelman, J. Comput. Chem., 28, 899(2007).47. N. L. Okamoto, K. Shimokawa, H. Tanimura, and T. Ichitsubo, Scr. Mater., 167,26 (2019).Electrochemistry, 92(2), 027003 (2024)6https://doi.org/10.50892/data.electrochemistry.24980718https://doi.org/10.1016/j.coelec.2020.01.017https://doi.org/10.1021/acsenergylett.1c00416https://doi.org/10.1002/advs.201500072https://doi.org/10.1039/C9CP01400Dhttps://doi.org/10.1039/C9CP01400Dhttps://doi.org/10.1016/j.jpowsour.2019.226822https://doi.org/10.1039/D1TA08115Bhttps://doi.org/10.1039/D1TA08115Bhttps://doi.org/10.1021/jp212415xhttps://doi.org/10.1149/2.009408jeshttps://doi.org/10.1021/acs.chemmater.6b04429https://doi.org/10.1063/1.5131447https://doi.org/10.1021/acs.jpcc.8b10625https://doi.org/10.1021/acs.jpcc.8b10625https://doi.org/10.1021/acsami.6b06157https://doi.org/10.1021/acsami.6b06157https://doi.org/10.1021/acsami.7b03435https://doi.org/10.1021/acs.jpcc.8b07848https://doi.org/10.1021/acs.jpcc.9b02096https://doi.org/10.1149/1945-7111/abf9c0https://doi.org/10.1149/1945-7111/abf9c0https://doi.org/10.1021/acs.jpcc.1c09244https://doi.org/10.1021/acs.jpcc.0c07550https://doi.org/10.1021/acs.langmuir.1c00197https://doi.org/10.1038/s41467-020-17126-3https://doi.org/10.1021/acs.jpcc.0c00565https://doi.org/10.1021/acs.jpcc.0c00565https://doi.org/10.1021/acsami.9b11942https://doi.org/10.1021/acs.jpcc.8b01713https://doi.org/10.1021/acs.jpclett.7b01655https://doi.org/10.1149/2.0431807jeshttps://doi.org/10.1016/j.electacta.2016.05.123https://doi.org/10.1021/acs.chemmater.9b00767https://doi.org/10.1021/acs.chemmater.9b00767https://doi.org/10.1021/acsami.7b09352https://doi.org/10.1021/acs.chemmater.2c03806https://doi.org/10.1021/acsenergylett.3c01084https://doi.org/10.1021/acsenergylett.3c01084https://doi.org/10.1063/1.4955135https://doi.org/10.1063/1.4955135https://doi.org/10.2138/am.2005.1559https://doi.org/10.1021/acs.chemmater.7b01252https://doi.org/10.1088/1361-648X/aa8f79https://doi.org/10.1103/PhysRevLett.78.1396https://doi.org/10.1103/PhysRevB.41.7892https://doi.org/10.1016/j.commatsci.2013.08.053https://doi.org/10.1016/j.commatsci.2013.08.053https://doi.org/10.1063/1.3382344https://doi.org/10.1063/1.3382344https://doi.org/10.1103/PhysRevB.71.035105https://doi.org/10.1016/j.apsusc.2022.156065https://doi.org/10.1016/j.apsusc.2022.156065https://doi.org/10.1016/j.apsusc.2016.05.096https://doi.org/10.1103/PhysRevB.73.115407https://doi.org/10.1016/j.commatsci.2005.04.010https://doi.org/10.1016/j.commatsci.2005.04.010https://doi.org/10.1088/0953-8984/21/8/084204https://doi.org/10.1088/0953-8984/21/8/084204https://doi.org/10.1063/1.3553716https://doi.org/10.1002/jcc.20575https://doi.org/10.1002/jcc.20575https://doi.org/10.1016/j.scriptamat.2019.03.034https://doi.org/10.1016/j.scriptamat.2019.03.034