Intrinsic Defect Energetics and Fluorine Doping Effects in Li2CO3 and Li2O2: A First-Principles Study

Keisuke Mukai; Nanako Ishihara; Shuji Nakanishi; Tasuku Sugiura; Teruyasu Mizoguchi; Youjeong Choi

arxiv: 2606.25408 · v1 · pith:U7JIQALInew · submitted 2026-06-24 · ❄️ cond-mat.mtrl-sci

Intrinsic Defect Energetics and Fluorine Doping Effects in Li2CO3 and Li2O2: A First-Principles Study

Youjeong Choi , Tasuku Sugiura , Keisuke Mukai , Nanako Ishihara , Shuji Nakanishi , Teruyasu Mizoguchi This is my paper

Pith reviewed 2026-06-25 21:05 UTC · model grok-4.3

classification ❄️ cond-mat.mtrl-sci

keywords Li2CO3Li2O2fluorine dopingdefect energeticsvacancy formation energyfirst-principleslithium-oxygen battery

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The pith

Fluorine doping lowers lithium and carbon vacancy formation energies selectively in Li2CO3 and lithium vacancy energy in Li2O2

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

This paper uses first-principles calculations to examine intrinsic point-defect energetics in Li2CO3 and Li2O2. Lithium-related defects dominate the intrinsic behavior in both compounds. Fluorine doping decreases lithium and carbon vacancy formation energies in Li2CO3 while also reducing the lithium vacancy formation energy in Li2O2. The changes indicate that doping can modulate the thermodynamic stability of these discharge products under conditions relevant to lithium-oxygen batteries.

Core claim

Intrinsic defect analysis reveals that defect behavior is predominantly governed by lithium-related defects. Upon fluorine doping, lithium and carbon vacancy formation energies decrease selectively in Li2CO3, partially destabilizing the carbonate framework, while a reduction in lithium vacancy formation energy is also observed in Li2O2. These results suggest that fluorine doping modulates the defect energetics of both discharge products, potentially providing a thermodynamic basis for controlling the stability of Li2CO3 and Li2O2 under thermodynamic conditions representative of lithium-oxygen batteries.

What carries the argument

First-principles calculations of vacancy formation energies before and after fluorine substitution, performed in supercells with chosen chemical potentials

If this is right

Lithium and carbon vacancy formation energies decrease selectively in Li2CO3 upon fluorine doping.
Lithium vacancy formation energy also decreases in Li2O2.
The carbonate framework experiences partial destabilization in Li2CO3.
Doping provides a thermodynamic route to influence stability of both discharge products.

Where Pith is reading between the lines

These are editorial extensions of the paper, not claims the author makes directly.

The selective energy reductions could alter relative decomposition rates of carbonate versus peroxide phases during cell operation.
Similar doping approaches might be explored in related alkali metal compounds to tune defect-controlled properties.
Validation through direct defect spectroscopy on doped samples would clarify applicability beyond the computed conditions.

Load-bearing premise

The first-principles defect energies computed under the chosen supercell and chemical-potential conditions accurately reflect thermodynamic stability under the operating conditions of lithium-oxygen batteries.

What would settle it

Experimental measurement of lithium or carbon vacancy concentrations in fluorine-doped Li2CO3 and Li2O2 samples at battery-relevant chemical potentials would directly test whether the computed energy reductions occur.

Figures

Figures reproduced from arXiv: 2606.25408 by Keisuke Mukai, Nanako Ishihara, Shuji Nakanishi, Tasuku Sugiura, Teruyasu Mizoguchi, Youjeong Choi.

**Figure 2.** Figure 2: Formation energies of intrinsic point defects in bulk Li2CO3 as a function of the Fermi level under voltage-dependent Li chemical potential: (a) 0 V, (b) 2.96 V, (c) 3.82 V vs. Li+/Li. The Fermi level is referenced to the valence band maximum and varied across the calculated band gap of Li2CO3. For Li vacancies, dashed lines represent the high formation energies. The voltage-dependent defect behavior of Li… view at source ↗

**Figure 3.** Figure 3: Formation energies of neutral vacancies in pristine (solid line) and fluorine-doped Li2CO3 (dashed and dotted lines) as a function of applied voltage U: (a) Li vacancy, (b) C vacancy, (c) O vacancy at O(f) site and (d) O vacancy at O(e) site. The gray shaded region indicates the equilibrium voltage of Li2CO3. The slopes observed for VLi 0 and VC 0 reflect the voltage dependence of 𝜇Li and 𝜇C through Eq. (2… view at source ↗

**Figure 4.** Figure 4: Formation energies of neutral vacancies in pristine and fluorine-doped Li2O2 as a function of applied voltage U: (a) Li vacancy at Li(a) site, (b) Li vacancy at Li(c) site, and (c) O vacancy. Li(a) and Li(c) denote two inequivalent Li sites, as defined in Figure S2. The gray shaded region indicates the equilibrium voltage of Li2O2 [PITH_FULL_IMAGE:figures/full_fig_p017_4.png] view at source ↗

read the original abstract

Lithium carbonate, Li2CO3, is a thermodynamically stable carbonate phase whose defect energetics are closely related to its stability and decomposition behavior in various lithium-based electrochemical systems. These properties of Li2CO3 are particularly important in lithium-oxygen battery environments. In these systems, Li2CO3 can form as a parasitic discharge product alongside Li2O2, the primary discharge product, leading to performance degradation. However, compared with Li2O2, the intrinsic defect thermodynamics of Li2CO3 and how chemical doping modifies its defect energetics remain insufficiently understood. In this study, first-principles calculations were performed to systematically analyze the intrinsic point-defect energetics of Li2CO3 and to evaluate the effects of fluorine doping on vacancy formation energies in Li2CO3 and Li2O2. Intrinsic defect analysis reveals that defect behavior is predominantly governed by lithium-related defects. Upon fluorine doping, lithium and carbon vacancy formation energies decrease selectively in Li2CO3, partially destabilizing the carbonate framework, while a reduction in lithium vacancy formation energy is also observed in Li2O2. These results suggest that fluorine doping modulates the defect energetics of both discharge products, potentially providing a thermodynamic basis for controlling the stability of Li2CO3 and Li2O2 under thermodynamic conditions representative of lithium-oxygen batteries.

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit. Tearing a paper down is the easy half of reading it; the pith above is the substance, this is the friction.

Desk Editor's Note private letter to a colleague

F doping lowers Li and C vacancy energies in Li2CO3 (and Li vacancies in Li2O2) according to their DFT runs, but the mapping to battery operating conditions rests on unshown chemical-potential choices.

read the letter

The main point is that fluorine doping appears to selectively reduce lithium and carbon vacancy formation energies in Li2CO3 while also lowering lithium vacancy energy in Li2O2. The authors frame this as a thermodynamic handle on the stability of these discharge products in Li-O2 cells.

They run standard first-principles defect calculations on both compounds, identify that lithium-related defects control the behavior, and then track how F substitution shifts the vacancy energies. That supplies concrete numbers for Li2CO3, which the abstract notes had been under-studied compared with Li2O2. The work is a straightforward extension of existing defect methods to these specific battery-relevant phases.

The calculations follow the usual formation-energy formula and supercell approach, so the numbers are in principle reproducible if the full methods section is solid. The selective effect on vacancies is the clearest new observation.

The weakest link is the claim that these energies reflect behavior under lithium-oxygen battery conditions. The abstract states the calculations use representative thermodynamic conditions, yet gives no explicit chemical-potential references, voltage adjustment, or sensitivity tests. If the potentials are referenced only to elemental phases rather than the cell voltage near 2.96 V, the reported drop in vacancy energies may not translate to operating stability. Without the actual numbers, error estimates, or convergence data, the magnitude of the effect is also hard to judge.

This is for modelers working on Li-O2 side reactions who want defect data on Li2CO3. A reader could extract useful trends, but would need to check the methods and chemical-potential section carefully before relying on the interpretation.

Send it to peer review. The calculations are standard and the topic is practical; the chemical-potential mapping is fixable with clearer justification or additional plots.

Referee Report

1 major / 1 minor

Summary. The manuscript reports first-principles DFT calculations of intrinsic point-defect energetics in Li2CO3 and Li2O2, with emphasis on vacancy formation energies, and evaluates the effects of fluorine doping on these energies. The central claims are that defect behavior is dominated by lithium-related defects, that F doping selectively lowers Li and C vacancy formation energies in Li2CO3 (partially destabilizing the carbonate), and that Li vacancy formation energy is also reduced in Li2O2, all under thermodynamic conditions stated to be representative of lithium-oxygen batteries.

Significance. If the computed formation energies remain representative when referenced to the electrochemical potentials set by Li-O2 cell operation, the results could supply a thermodynamic rationale for using F doping to modulate stability of parasitic Li2CO3 versus the desired Li2O2 product. The work employs standard supercell defect methodology and formation-energy formulas; its value would be strengthened by explicit validation or sensitivity checks against experimental defect data or voltage-dependent conditions.

major comments (1)

[Abstract] Abstract and (presumed) Methods/Results sections: the claim that calculations are performed “under thermodynamic conditions representative of lithium-oxygen batteries” is load-bearing for the interpretation that the reported decreases in vacancy energies imply destabilization under operating conditions. No explicit justification, chemical-potential references (Li, C, O, F), finite-size corrections, or sensitivity analysis to the ~2.96 V cell voltage is supplied in the provided text; if the potentials are instead taken from elemental phases or the Li2CO3/Li2O2 equilibrium without voltage adjustment, the selective lowering may not translate to the battery regime.

minor comments (1)

[Abstract] The abstract supplies no numerical formation-energy values, supercell sizes, or error estimates; inclusion of at least representative numbers and a brief statement of convergence would improve immediate assessability.

Simulated Author's Rebuttal

1 responses · 0 unresolved

We thank the referee for the constructive feedback. We address the single major comment below and will revise the manuscript accordingly to strengthen the presentation of thermodynamic conditions.

read point-by-point responses

Referee: [Abstract] Abstract and (presumed) Methods/Results sections: the claim that calculations are performed “under thermodynamic conditions representative of lithium-oxygen batteries” is load-bearing for the interpretation that the reported decreases in vacancy energies imply destabilization under operating conditions. No explicit justification, chemical-potential references (Li, C, O, F), finite-size corrections, or sensitivity analysis to the ~2.96 V cell voltage is supplied in the provided text; if the potentials are instead taken from elemental phases or the Li2CO3/Li2O2 equilibrium without voltage adjustment, the selective lowering may not translate to the battery regime.

Authors: We agree that explicit details on chemical-potential references, finite-size corrections, and relation to cell voltage would improve clarity. The calculations reference Li to bcc-Li, C to graphite, O to O2(g), and F to F2(g) at standard states, with formation energies computed via the standard supercell formula; finite-size corrections follow the FNV scheme. The doping-induced reductions in vacancy energies are relative quantities and thus independent of the absolute reference; these trends remain informative for battery conditions even if absolute values shift with voltage. We will add an explicit subsection in Methods/Results detailing the references, confirming FNV corrections were used, and providing a short discussion of how the reported trends map onto the ~2.96 V Li-O2 equilibrium (including a one-paragraph sensitivity note). revision: yes

Circularity Check

0 steps flagged

No circularity detected; derivation is self-contained first-principles computation

full rationale

The paper computes intrinsic point-defect formation energies and fluorine-doping effects in Li2CO3 and Li2O2 via standard DFT supercell calculations and the conventional defect formation-energy formula. No fitted parameters are renamed as predictions, no self-definitional loops appear in the energy expressions, and no load-bearing uniqueness theorems or ansatzes are imported from the authors' prior work. The central results follow directly from the electronic-structure calculations under stated chemical-potential references; the mapping to battery conditions is an interpretive step external to the numerical derivation itself.

Axiom & Free-Parameter Ledger

0 free parameters · 1 axioms · 0 invented entities

Abstract-only review yields no explicit free parameters, invented entities, or non-standard axioms; the work implicitly relies on standard DFT assumptions for defect formation energies.

axioms (1)

domain assumption Standard density-functional-theory approximations and supercell boundary conditions suffice to compute formation energies of point defects in these ionic solids.
Implicit in any first-principles defect study of this type.

pith-pipeline@v0.9.1-grok · 5810 in / 1069 out tokens · 23659 ms · 2026-06-25T21:05:05.581888+00:00 · methodology

discussion (0)

Reference graph

Works this paper leans on

4 extracted references · 3 canonical work pages

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[1] [1]

D.; Siegel, D

(1) Radin, M. D.; Siegel, D. J. Charge Transport in Lithium Peroxide: Relevance for Rechargeable Metal –Air Batteries. Energy Environ. Sci. 2013, 6 (8),

2013

[2] [2]

(2) Cortes, H

https://doi.org/10.1039/c3ee41632a. (2) Cortes, H. A.; Vildosola, V. L.; Barral, M. A.; Corti, H. R. Effect of Halogen Dopants on the Properties of Li 2 O2 : Is Chloride Special? Phys. Chem. Chem. Phys. 2018, 20 (25), 16924– 16931. https://doi.org/10.1039/C8CP01211C. (3) Thomas C. Allison. NIST -JANAF Thermochemical Tables - SRD 13,

work page doi:10.1039/c3ee41632a 2018

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(4) Idemoto, Y.; Richardson, J

https://doi.org/10.18434/T42S31. (4) Idemoto, Y.; Richardson, J. W.; Koura, N.; Kohara, S.; Loong, C. -K. Crystal Structure of (LixK1 − x)2CO3 (x = 0, 0.43, 0.5, 0.62,

work page doi:10.18434/t42s31

[4] [4]

Journal of Physics and Chemistry of Solids 1998, 59 (3), 363 –376

by Neutron Powder Diffraction Analysis. Journal of Physics and Chemistry of Solids 1998, 59 (3), 363 –376. https://doi.org/10.1016/S0022 - 3697(97)00209-6

work page doi:10.1016/s0022 1998