Cation mixing is read from the I(003)/I(104) ratio for every material (1.05 to 1.45, Tables II.5–II.9) and refined only for two: 3.5 % Li/Ni antisite in NMA and 2.2 % in La–NMA (p. 90). Every dopant is said to reduce mixing, and the electrochemistry is explained by it (Chapter III).

I(003)/I(104) is a proxy that also moves with preferred orientation, absorption and the oxygen position; it is not an occupancy. More important, charge balance requires Ni\(^{2}\)⁺, the species that mixes, in every Mn-containing material: 0.05–0.15 Ni\(^{2}\)⁺ per formula unit (fact base), rising with Mn, while the ratio is read as falling mixing. X-rays see Ni on the Li layer well (3 % exchange changes the Cu Kα pattern by 6.5 %), but they cannot tell Ni from Mn there (Z 28 and 25: 0.2 %). Neutrons can (b 10.3 against −3.73 fm: 6.9 %, 33 times more).

Li/Ni mixing by neutrons and joint X-ray/neutron refinement is well established for \(\mathrm{LiNiO_{2}}\), NCA and NMC (Rougier et al. 1996; Pouillerie et al. 2001; Goonetilleke et al. 2023; Kurzhals et al. 2021: 1.6–3.7 % Ni on the Li layer of \(\mathrm{LiNiO_{2}}\)), and joint refinement reaches about 0.1 % antisite sensitivity (Yin et al. 2018). I(003)/I(104) gives the mixing only after a preferred-orientation correction and within one disordering scheme (Orlova et al. 2021, X-rays). No neutron refinement of Co-free NMA was found, and no study uses Mn's negative scattering length to tell Mn from Ni on the Li layer.

Neutron powder diffraction at high resolution (ILL D2B) refined jointly with synchrotron data (ESRF ID22) in diff-ref-struct: Li, Ni and Mn on both layers, constrained by ICP and charge balance.

The key set K9.

The Ni (and Mn) on the Li layer of each material, with esd; the dopant ranking of the thesis tested against refined values; the I(003)/I(104) proxy calibrated against the refined mixing on nine materials of one laboratory.

Li/Ni mixing is the thesis's explanation of capacity, efficiency and retention for every dopant. Measured, it becomes its central structural result.

ICP-OES gives Li 0.6–0.9 wt% below nominal in all four Co-reduction materials, called a modest deficiency from volatilisation or surface LiOH/\(\mathrm{Li_{2}CO_{3}}\) (Table II.4, p. 70).

Converted to formula units, Table II.4 gives 0.908–0.932 Li per transition metal: a 7–9 % deficit. If it is real and in the bulk, the cathodes are Li₁₋ₓNi₁₊ₓO₂-like and Ni must fill the Li layer; if part of the Li is in surface carbonate and hydroxide, the bulk deficit is larger still. Lithium carries 1 % of the X-ray scattering of NMA; neutrons see it in antiphase to the metals.

Li₁₋ₓNi₁₊ₓO₂ non-stoichiometry is the classic defect of these oxides (Rougier et al. 1996; Goonetilleke et al. 2023); the Li/Ni ratio of the synthesis controls it more than temperature (Kurzhals et al. 2021). Ex situ neutron diffraction refines Li occupancy in NCA at every state of charge (Hölderle et al. 2023).

Neutron diffraction (D2B) for the Li occupancy, jointly with ID22; ICP-OES on washed and unwashed powder; titration of surface lithium species; TGA–MS.

K9, fresh and as stored.

The bulk Li per formula unit of each material and the surface Li species, separated; a Li balance consistent with the refined Ni on the Li layer.

Lithium inventory sets the first-cycle efficiency (63 % for NCA, 98 % for NMA, 81 % for La–NMA: Table III.2, p. 136), which the thesis reads without it.

Mn is assumed to replace Co on its site in the Mn–NCA series; the oxidation states of Ni, Mn and Co are not measured (XPS of Ni and Sb is not reported); the redox plateau is assigned to Ni\(^{2}\)⁺/Ni\(^{4}\)⁺ (p. 123).

Ni, Co and Mn differ by one to three electrons; on the same site X-rays hardly separate them (Mn for Ni 0.16 %, Co for Ni 0.19 %). Neutrons separate them by sign and size (10.3, 2.49, −3.73 fm): 6.6 and 6.2 %, 35–40 times more. Oxidation states need X-ray absorption: Ni, Mn and Co K edges.

Al in NCA is octahedral and homogeneous (Trease et al. 2016, with neutrons and NMR); Mn stays on its site on heating while Co migrates (Bak et al. 2014). 5 % Mn or Al in \(\mathrm{LiNiO_{2}}\) delays the H2–H3 transition (Adamo and Manthiram 2024). The Mn-for-Co series of this thesis is published by the candidate (El Kouihen et al. 2026, J. Energy Storage) from laboratory XRD.

Neutron diffraction (D2B) for the layer composition; Ni K, Mn K and Co K XANES (ESRF BM23) for Ni\(^{2}\)⁺/Ni\(^{3}\)⁺, Mn\(^{4}\)⁺ and Co\(^{3}\)⁺.

NCA, 5 % Mn–NCA, 10 % Mn–NCA, NMA, Fe/Sb–NMA.

The mean Ni oxidation state of each material, set against the charge-balance prediction (Ni 3.00 in NCA down to 2.81 in NMA); the Mn and Co contents of the TM layer.

The Co-to-Mn replacement is the first design line of the thesis; whether Mn enters as Mn\(^{4}\)⁺ with Ni\(^{2}\)⁺, and where the Ni\(^{2}\)⁺ goes, decides what it does to the structure.

All five are said to be incorporated, from lattice shifts and the absence of extra peaks: Mg, Y, La on the TM layer (p. 88), Sc on the Mn site and Na on the Li site (p. 98). La\(^{3}\)⁺ (1.03 Å) and Y\(^{3}\)⁺ (0.90 Å) are much larger than any TM ion of the layer.

The site of a dopant at 3 mol % is a small change on any probe. X-rays see Y and La best (10–15 % between the TM and the Li layer), neutrons Mg and Sc slightly better than X-rays; Na is seen equally. Second phases (La- or Y-rich oxides, Na-rich layers) below a few per cent are invisible in laboratory data; surface segregation is invisible to diffraction altogether.

Mg goes first to the Ni site up to about 1.7 % and then to the Li site (Weber et al. 2022, synchrotron XRD); in Mg/Mn-\(\mathrm{LiNiO_{2}}\) Mg sits on the Li site (Mu et al. 2020). Y forms a surface gradient by segregation (Wang et al. 2021); La forms a \(\mathrm{La_{2}Ni_{0}}\).₅Li₀.₅O₄ surface layer on NCM811 (Wu et al. 2019). Dopants added at co-precipitation enter the lattice, at lithiation they stay as a phase (Colalongo et al. 2024, Zr, synchrotron XRD + XAS), the closest template for this route. No site-resolved evidence was found for Sc or Na.

High-resolution synchrotron diffraction (ID22) for the site of Y and La and for second phases to \(\approx 0.1\) wt%; neutrons (D2B) for Mg; Y K, La K and Sc K X-ray absorption (BM23; BM08 or BM20 for Sc) for the local environment.

Mg–, Y–, La–, Sc–, Na–NMA and the pristine NMA.

For each dopant: the fraction on the TM layer, on the Li layer, and in a second phase or at the surface.

The best retention of the thesis (La–NMA 96.3 %, Y–NMA 92.9 % after 200 cycles) is explained by incorporation into the lattice; a surface phase would be a different mechanism, a coating.

Sb\(^{3}\)⁺ is said to oxidise to Sb\(^{5}\)⁺ during calcination (p. 79), while §II.3.2 lists Sb\(^{3}\)⁺ among the trivalent dopants; Fe\(^{3}\)⁺ is placed on the TM layer. The Fe/Sb–NMA formula of §II.4.4 has 1.10 metals per formula unit, and Table II.10's own theoretical values correspond to about Ni₀.₇₆Mn₀.₀₈Fe₀.₀₅Sb₀.₀₅Al₀.₀₆.

Valence is not a diffraction quantity. Fe on the Li layer, known in \(\mathrm{LiNi_{1}}\)₋ₓFeₓO₂, changes the X-ray and neutron patterns about equally (5–6 %); Sb on the Li layer is an X-ray question (14 % in Cu Kα). With Sb\(^{5}\)⁺ and Fe\(^{3}\)⁺ charge balance requires 0.10 Ni\(^{2}\)⁺ in Fe/Sb–NCA, more Ni to mix, not less.

Fe in Li(Ni,Fe)O₂ sits on both the slab and the interslab sites at high substitution (Prado et al. 2000, X-rays, neutrons and ⁵⁷Fe Mössbauer), the only direct precedent. Fe and Ni have similar neutron scattering lengths (9.45 and 10.3 fm), so the Fe site needs resonant X-rays at the Fe K edge or Mössbauer. No Sb K-edge XAS or Sb site refinement was found for Ni-rich cathodes; Sb doping is argued from surface oxygen retention (Cheng et al. 2020).

Sb K (30.49 keV) and Fe K XANES/EXAFS (BM23); resonant diffraction at the Fe K edge (ID22) for the Fe site, since Fe and Ni scatter neutrons alike; ⁵⁷Fe Mössbauer where available; the joint refinement (D2B + ID22) with the ICP composition.

Fe/Sb–NCA, Fe/Sb–NMA, and their pristine references.

The valence of Sb and Fe, the site of Fe, and one formula per material that closes against ICP and charge.

The co-doped NMA has the best retention of the thesis (96.7 %); its composition is not yet one number.

Li–O distances of 2.363–2.395 Å are reported (Tables II.5, II.9), which require a refined oxygen position; thermal stability is argued from TGA mass loss of the lithiated powders (pp. 73, 81).

The oxygen position and occupancy carry 15 % of the X-ray scattering of NMA and 42 % of the neutron scattering: neutrons are 2–2.5 times more sensitive (o-z, o-vac). TGA of a lithiated powder measures surface species and moisture, not the oxygen release of a charged cathode, which is what thermal stability means for a battery.

On heating, charged NMC releases O₂ and turns to rock salt, earlier the more Ni it holds (Bak et al. 2014; Jung et al. 2017; Geng et al. 2020 with ex situ neutrons). No in situ heating synchrotron study of doped NMA was found.

Neutrons (D2B) for z(O) and occupancy; in situ heating synchrotron diffraction of charged (delithiated) electrodes (ID22 hot-air blower or ID15A oven) for the layered → spinel → rock-salt sequence and its onset temperature.

NMA, La–NMA, Y–NMA, Fe/Sb–NMA, charged to 4.5 V.

z(O), the Li-slab and TM-slab thicknesses with esd; the onset temperature of the phase transitions of each charged cathode.

It replaces a thermal-stability claim based on powders by the measurement that defines it.

The same pristine NMA appears with a = 2.9042, c = 14.3489 Å (Table II.3) and a = 2.860, c = 14.30 Å (Tables II.7–II.9); c/a = 5.00–5.08 for the NMA family against 4.94 for NCA.

Both NMA cells are far from each other (1.5 % in a) and from the values usually reported for Ni-rich NMA (c/a \(\approx 4.94\text{–}4.95\)); c/a near 5.0 is unusual for a layered oxide of this composition. A zero-shift or calibration problem in the laboratory data is the likely cause; no standard or zero-shift treatment is stated.

High-resolution synchrotron diffraction of all twelve powders with an internal standard (ID22).

All twelve materials (A12).

One lattice parameter set with esd per material, from one instrument and one protocol; the dopant trends of a, c and c/a re-read on it.

Every lattice-shift argument of Chapter II (incorporation, expansion with ionic radius) rests on these numbers.

No secondary phases detected in any material (Chapter II), from laboratory patterns.

\(\mathrm{Li_{2}CO_{3}}\) and LiOH on Ni-rich surfaces, a NiO-like rock-salt fraction, and La-, Y- or Sc-rich oxides at the per-cent level are at or below laboratory detection, and Mn, Co and Fe fluoresce under Cu Kα (their K edges are below 8.05 keV), raising the background of exactly these samples unless the detector discriminates.

High-resolution synchrotron diffraction (ID22), detection limits \(\approx 0.1\) wt%.

All twelve.

The phase content of each powder with detection limits; the surface lithium species quantified.

Secondary phases change the capacity per gram and the interface, and can masquerade as dopant effects.

Retention after 200 cycles (NMA 76.5 %, Y–NMA 92.9 %, La–NMA 96.3 %, Fe/Sb–NMA 96.7 %) is explained by reduced mixing and better ordering; the Perspectives ask for operando XRD and synchrotron techniques (p. 183).

Structural evolution on cycling is not measured: no operando or ex situ diffraction of electrodes.

Operando synchrotron diffraction of the H2–H3 transition and the c collapse of Ni-rich cathodes is routine (Li et al. 2018; Jousseaume et al. 2024; Liu et al. 2023), including XRD-CT of an NCA 18650 at ESRF ID31 (Matras et al. 2022); operando neutron diffraction of pouch cells with natural Li works (Menon et al. 2026, ISIS WISH). The doped NMA of this thesis has not been studied so.

Operando synchrotron diffraction in coin or pouch cells (ESRF ID31 or ID15A) over the first charge to 4.5 V and early cycles; ex situ neutron diffraction (D2B) of electrodes after 200 cycles for the Ni on the Li layer.

NMA, Y–NMA, La–NMA, Fe/Sb–NMA.

The c-axis collapse and H2–H3 coexistence of each material against state of charge; the Li/Ni mixing after cycling against the pristine.

It tests the mechanism the thesis gives for its best retention.

About 1 wt% \(\mathrm{LiNbO_{3}}\) coating improves the NMA | \(\mathrm{Li_{6}PS_{5}Cl}\) | Li–In cell (73.8 % against 60.1 % after 50 cycles, §IV.3.2); coating thickness, crystallinity and Nb diffusion are not determined.

A nanometre coating of 1 wt% is invisible to laboratory diffraction; whether it is crystalline \(\mathrm{LiNbO_{3}}\), amorphous, or Nb dissolved in the surface of the cathode decides its role.

\(\mathrm{LiNbO_{3}}\) and \(\mathrm{Li_{2}CO_{3}}\)/\(\mathrm{LiNbO_{3}}\) coatings on NCM with β-\(\mathrm{Li_{3}PS_{4}}\) and \(\mathrm{Li_{6}PS_{5}Cl}\) are studied by XPS, ToF-SIMS and FIB-SEM (Kim et al. 2019, 2021; Walther et al. 2021); Nb from a coating step also enters the bulk of NMC811 and NMC9055 (Xin et al. 2019, 2022). An operando neutron cell for solid-state batteries exists at the ILL (ILLBAT; Korjus et al. 2025; Anil Kumar et al. 2025, preprint). Nothing on \(\mathrm{LiNbO_{3}}\)-coated Co-free NMA.

Nb K XAS (18.99 keV, BM23); X-ray total scattering (ID15A) for an amorphous coating; synchrotron diffraction of the composite before and after cycling.

Coated and pristine NMA, and their composite cathodes before and after cycling.

The state and location of Nb; the interface phases after cycling.

Second round: the link to the solid-state strand of the joint project (the garnet electrolytes of the first project).