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arxiv: 1906.09416 · v1 · pith:K23SMF63new · submitted 2019-06-22 · ❄️ cond-mat.mtrl-sci

Chemical induced delithiation on LixMnPO4: an investigation about the phase structure

Melanie K\"ontje , Giorgia Greco , Giuliana Aquilanti , Luca Olivi , Peter Axmann , Margret Wohlfahrt-Mehrens This is my paper

Pith reviewed 2026-05-25 18:19 UTC · model grok-4.3

classification ❄️ cond-mat.mtrl-sci
keywords chemical delithiationLixMnPO4cerimetric analysisoxidation stateX-ray absorption spectroscopylithium manganese phosphatephase transition
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The pith

Cerimetric analysis of chemically delithiated LixMnPO4 shows lithium content and oxidation state do not match.

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

The paper examines the phases created by chemically removing lithium from LixMnPO4 using nitronium tetrafluoroborate in acetonitrile. XRD and ICP-OES results align with earlier studies on the LiMnPO4 to MnPO4 transition, yet cerimetric titration finds clear differences between the measured lithium removal and the average manganese oxidation state. The work also applies XAS to map local atomic and electronic structure in both bare and carbon-coated samples at nominal compositions x=0.45 and x=0.23-0.24. A sympathetic reader would care because any mismatch between bulk lithium content and redox state implies that nominal delithiation levels do not produce the expected single-phase or two-phase mixtures. This directly affects how the material's electrochemical performance is interpreted and improved.

Core claim

Standard materials characterization with XRD and ICP-OES analysis are in accordance with literature data, but further cerimetric analysis revealed serious deviations, showing differences in the degree of delithiation to the average degree of oxidation. A structural characterization of the atomic and electronic local structure of the materials is also obtained using XAS technique.

What carries the argument

Cerimetric titration applied after chemical delithiation with excess nitronium tetrafluoroborate, used to quantify average oxidation state separately from lithium content measured by ICP-OES.

If this is right

  • The LiMnPO4/MnPO4 two-phase region may contain additional redox processes beyond simple lithium extraction.
  • Carbon coating changes the observed delithiation behavior compared with bare material.
  • XAS local-structure data can be used to distinguish phases even when bulk oxidation state deviates from nominal composition.
  • Electrochemical cycling studies of these samples would need to account for the actual rather than nominal lithium content.

Where Pith is reading between the lines

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

  • If side reactions consume part of the oxidant without removing lithium, similar titration discrepancies could appear in other olivine phosphates prepared by the same route.
  • The mismatch suggests that reported phase diagrams for chemically delithiated LixMnPO4 may need revision once oxidation state is measured independently of lithium content.
  • Testing whether the deviation scales with the amount of excess oxidant used would clarify whether the effect is intrinsic to the material or procedural.

Load-bearing premise

The chemical delithiation procedure produces samples whose lithium content exactly matches the nominal x values without side reactions or solvent effects that alter the measured oxidation state independently of lithium removal.

What would settle it

Repeat the cerimetric titration and ICP-OES measurements on freshly prepared batches while tracking total manganese content and any soluble manganese species in the delithiation solution; consistent mismatch would support the claim while exact agreement would falsify it.

read the original abstract

Understanding the LiMnPO4/MnPO4 phase transition is of great interest in order to further improve the electrochemical performance of this cathode material. Since most of the previously published literature deals with characterization of chemically delithiated Lix MnPO4, the aim of this study is to compare and study the composition and structure of the different phases that are generated upon chemical delithiation of LixMnPO4. Bare and carboncoated lithium manganese phos-phates are prepared via a combined coprecipitation-calcination method. Partial delithiation to two different degrees of delithiation Lix MnPO4 (x = 0.24/0.23 and 0.45) for carbon-coated and/or bare materials is achieved using an excess of nitro-nium tetrafluoroborate in acetonitrile. The effect of carboncoating has been also considered. Standard materials characterization with XRD (X-Ray Diffraction) and ICPOES (Inductive Coupled Plasma spectrometry and Optical Emission Spectroscopy) analysis are in accordance with literature data, but further cerimetric analysis revealed serious deviations, showing differences in the degree of delithiation to the average degree of oxidation. A structural characterization of the atomic and electronic local structure of the materials is also ob-tained using XAS (X-ray Absorption Spectroscopy) technique.

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.

Referee Report

2 major / 2 minor

Summary. The manuscript examines chemical delithiation of bare and carbon-coated LiMnPO4 to nominal compositions LixMnPO4 (x ≈ 0.24/0.23 and 0.45) using excess nitronium tetrafluoroborate in acetonitrile. Standard characterization via XRD and ICP-OES is reported to agree with literature values on the LiMnPO4/MnPO4 two-phase system, while cerimetric titration is claimed to reveal significant deviations between the degree of delithiation and the average Mn oxidation state. XAS is additionally employed to characterize local atomic and electronic structure, with consideration of the carbon-coating effect.

Significance. If the cerimetric deviations prove to reflect genuine material behavior rather than analytical interference, the work would underscore limitations of chemical delithiation for isolating phase-pure LixMnPO4 intermediates and could inform better protocols for studying the olivine phosphate two-phase transition. The dual-sample (bare/coated) design and XAS component provide a modest incremental contribution to the existing literature on LiMnPO4 delithiation.

major comments (2)
  1. [Results / Cerimetric analysis] Cerimetric analysis (results section): The central claim of 'serious deviations' between nominal/ICP-OES delithiation degree and average oxidation state is load-bearing, yet the manuscript provides no calibration curves, blank runs on delithiation solvent, recovery tests on Mn standards, or controls for carbon-coating interference on the redox endpoint. This directly addresses the stress-test concern that residual acetonitrile or coating effects could produce the reported discrepancy independently of lithium content.
  2. [Abstract / Experimental] Abstract and experimental methods: No quantitative values, error bars, replicate counts, or statistical comparison between ICP-OES and cerimetric results are supplied, preventing assessment of whether the deviations exceed measurement uncertainty and undermining evaluation of the phase-structure interpretation.
minor comments (2)
  1. [Abstract] Typos and formatting: 'carboncoated' and 'phos-phates' should be corrected; 'ob-tained' appears as a line-break artifact.
  2. [Discussion] The link between the observed oxidation-state deviations and specific phase-structure features (e.g., via XAS) is stated but not quantitatively developed in the abstract; a clearer mapping in the discussion would strengthen the narrative.

Simulated Author's Rebuttal

2 responses · 0 unresolved

We thank the referee for the constructive comments. We address the major points below and will incorporate the requested information in a revised manuscript.

read point-by-point responses

  1. Referee: [Results / Cerimetric analysis] Cerimetric analysis (results section): The central claim of 'serious deviations' between nominal/ICP-OES delithiation degree and average oxidation state is load-bearing, yet the manuscript provides no calibration curves, blank runs on delithiation solvent, recovery tests on Mn standards, or controls for carbon-coating interference on the redox endpoint. This directly addresses the stress-test concern that residual acetonitrile or coating effects could produce the reported discrepancy independently of lithium content.

    Authors: We agree that explicit validation of the cerimetric procedure is needed to support the central claim. In the revised manuscript we will add calibration curves for the titration, blank measurements on the delithiation solvent, recovery tests with Mn standards, and controls assessing possible interference from residual acetonitrile or the carbon coating. revision: yes

  2. Referee: [Abstract / Experimental] Abstract and experimental methods: No quantitative values, error bars, replicate counts, or statistical comparison between ICP-OES and cerimetric results are supplied, preventing assessment of whether the deviations exceed measurement uncertainty and undermining evaluation of the phase-structure interpretation.

    Authors: We will revise the abstract and methods sections to report the quantitative lithium contents and average oxidation states obtained by both ICP-OES and cerimetry, together with error bars, the number of replicate measurements, and a direct statistical comparison of the two techniques. revision: yes

Circularity Check

0 steps flagged

No circularity: purely experimental measurements with no derivations or self-referential predictions

full rationale

The paper is an experimental study involving material synthesis, chemical delithiation, and characterization via XRD, ICP-OES, cerimetric analysis, and XAS. No equations, fitted parameters, predictions, or derivation chains are present in the abstract or described content. All results stem from independent laboratory measurements rather than any self-definition, fitted inputs renamed as predictions, or self-citation load-bearing arguments. This matches the default expectation for non-circular experimental reports.

Axiom & Free-Parameter Ledger

0 free parameters · 1 axioms · 0 invented entities

The central claim depends on the assumption that the chosen chemical delithiation method produces well-defined lithium stoichiometries and that cerimetric titration accurately reports the average manganese oxidation state without interference from the carbon coating or residual solvent.

axioms (1)
  • domain assumption Nitronium tetrafluoroborate in acetonitrile achieves partial delithiation to the stated nominal x values (0.24/0.23 and 0.45) in both bare and carbon-coated LixMnPO4 without side reactions that would decouple lithium removal from manganese oxidation.
    Invoked when the authors prepare the two degrees of delithiation and compare them to expected oxidation states.

pith-pipeline@v0.9.0 · 5796 in / 1486 out tokens · 35741 ms · 2026-05-25T18:19:01.797578+00:00 · methodology

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Reference graph

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