Lithium-rich materials with anionic redox are promising candidates for high-energy-density positive electrodes. Manganese-based compounds like Li2MnO3 offer advantages, including low toxicity and abundant resources, but suffer from poor rate capability due to irreversible oxygen loss and structural transformation. Here, we study an O2-type layered oxide LiMn0.75O2, which shows significantly enhanced cycling stability, retaining 78% of its capacity after 140 cycles, with suppressed structural reorganization and more reversible oxygen redox. By combining electrochemical analysis with operando X-ray absorption spectroscopy (XAS) and pair distribution function measurements (PDF), we provide a detailed picture of the material's structural and redox evolution. The first charge differs markedly from subsequent cycles, combining partially reversible bulk oxygen redox, irreversible Li extraction from surface regions, and impurities with oxygen gas release. From the second cycle onward, the reversible bulk oxygen redox process becomes progressively activated. Besides, no clear evidence of short O-O dimers are observed in PDF, suggesting a limited degree of oxygen dimerization during the oxygen redox. Overall, this work showcases the high-capacity potential of Mn-based Li-rich materials, deepens understanding of their redox behavior, and underscores the power of PDF-based operando techniques in probing local structural changes during cycling.

Layered Na x MO2 sodium oxide positive electrode materials have experienced renewed interest owing to the current commercial attention on sodium-ion batteries. Although there are many attractive qualities of these materials, they suffer from serious shortcomings owing to Na+ ordering and transition-metal layer gliding that cause a plethora of voltage plateaus during cycling. The P2-layered Na2+x Ni2-x/2TeO6 (0 ≤ x ≤ 0.5) system provides a framework for investigating the effect of dual Na+ substitution into the sodium layer and the transition-metal layer of the structure and its effects on the electrochemical properties of the materials. A careful investigation into the synthesis and properties of these materials reveals that the sodium content used during material preparation has a drastic effect on the composition and electrochemical profile of these materials. The sodium substitution disrupts ordering within the transition-metal layer, thereby disrupting Na+ ordering in the adjacent sodium layers. Beyond a critical sodium concentration, the layer stacking shifts, and all voltage plateaus of the P2-Na2Ni2TeO6 material are no longer observed at 4.4 V versus Na+/Na. These results also question the common belief that additional sodium precursor is required when preparing layered sodium oxide cathodes, providing new guidelines for material synthesis and characterization.

Lithium‐rich materials with anionic redox are promising candidates for high‐energy‐density positive electrodes. Manganese‐based compounds like Li 2 MnO 3 offer advantages, including low toxicity and abundant resources, but suffer from poor rate capability due to irreversible oxygen loss and structural transformation. Here, we study an O2‐type layered oxide LiMn 0.75 O 2 , which shows significantly enhanced cycling stability, retaining 78% of its capacity after 140 cycles, with suppressed structural reorganization and more reversible oxygen redox. By combining electrochemical analysis with operando X‐ray absorption spectroscopy (XAS) and pair distribution function measurements (PDF), we provide a detailed picture of the material's structural and redox evolution. The first charge differs markedly from subsequent cycles, combining partially reversible bulk oxygen redox, irreversible Li extraction from surface regions, and impurities with oxygen gas release. From the second cycle onward, the reversible bulk oxygen redox process becomes progressively activated. Besides, no clear evidence of short O–O dimers are observed in PDF, suggesting a limited degree of oxygen dimerization during the oxygen redox. Overall, this work showcases the high‐capacity potential of Mn‐based Li‐rich materials, deepens understanding of their redox behavior, and underscores the power of PDF‐based operando techniques in probing local structural changes during cycling.

Understanding ion diffusion mechanisms in layered materials is critical for advancing next-generation battery technologies. Using the well-characterized NaxCoO2 (NCO) system as a model platform, we investigated the temperature-dependent diffusion properties across a broad compositional range (x = 0.33-0.89) using muon spin relaxation (mu +SR). Unexpected low-temperature internal magnetic field fluctuations were observed, systematically varying with Na content and appearing well before the onset of long-range diffusion. These fluctuations are attributed to phonon-assisted local Na motion, as suggested by a systematic increase in A with x, concurrent with a decreasing activation energy. The diffusion coefficient was calculated based on the crystal structure using a tailored diffusion model accounting for two inequivalent Na sites, yielding values consistent with those found in other layered battery materials. This work highlights the crucial role of phonon-coupled diffusion mechanisms in enabling ion transport at the microscopic scale, providing new insights into ion dynamics in layered solid-state conductors and their relevance to sodium-ion battery technology.

In this presentation 23 Na MAS NMR was used to probe the local structure, electronic structure and dynamics in several layered Na x MO 2 oxides for application in Na-ion batteries. Among them, P2-Na x CoO 2 appears to be a model material with a very specific phase diagram and unusual physical properties. 23 Na MAS NMR was used to characterize the changes in the electronic structure during Na deintercalation. 23 Na MAS was also used to characterize the local structure and dynamics versus temperature in several P2 or P3 Na x CoO 2 materials and P2-Na 1/2 VO 2 . In the latter, an increase of two orders of magnitude in its electronic conductivity has been observed at approximately 322 K and a structural transition has been found to occur simultaneously. At room temperature, high resolution powder diffraction and pair distribution function analysis reveal the triangular lattice formed by vanadium ions to be distorted by the formation of pseudo-trimers vanadium clusters. At 350 K, the mobility of the electronic charge carried by vanadium ions increases as evidenced by the increase in the electronic conductivity. The arrangement of sodium ordering in P2-Na 1/2 VO 2 , which maximizes sodium-sodium distances to lower electrostatic repulsions between alkali ions, is found to be unchanged across this transition, but the ionic mobility as observed by NMR, clearly change. Finally, the P2- Na 2+x Ni 2-x/2 TeO 6 (0 ≤ x ≤ 0.5) system provides a framework for investigating the effect of dual Na + substitution into the sodium layer and the transition-metal layer of the structure, and its effects on the electrochemical properties of the materials. The sodium substitution disrupts ordering within the transition-metal layer thereby disrupting Na + ordering in the adjacent sodium layers. Beyond a critical sodium concentration, the layer stacking shifts, and all voltage plateaus of the P2-Na 2 Ni 2 TeO 6 material are no longer observed. These results highlight how sodium ordering between the MO 2 layers and the electronic transport within the MO 2 layers are intimately correlated in Na x MO 2 type sodium layered oxides.

The assertion of intrinsic material properties based on measured experimental data is being challenged by emerging sample synthesis protocols, which opens new avenues for discovering novel functionalities. In this study, we revisit one of the most widely studied strongly correlated materials of the early 2000s, Na_{x}CoO_{2} (NCO). Leveraging the sensitivity of muon spin rotation and relaxation (μ^{+}SR) measurements, we discern significant differences between NCO samples synthesized via conventional solid-state reaction (SSR) and our electrochemical reaction (ECR) approach. Contrary to SSR-synthesized Na_{0.7}CoO_{2}, which exhibits a nonmagnetic ground state, our ECR-derived sample showcases an antiferromagnetic (AF) order from x≥0.7, challenging established phase boundaries. We attribute the observed magnetic phenomena in ECR-NCO to long-range order of Na-ions and/or vacancies, as well as the inherent flexibility of the crystal framework. Our study holds implications for tailoring and optimization of next-generation devices based on layered materials.

A cobalt-free manganese-based lithium-rich layered oxide with an unusual O6-type structure has been successfully synthesized by solid-state ion-exchange reaction from the intermediate P2-type sodium-based layered oxide precursor Na5/6[Li1/6Ni1/6Mn4/6]O2 using lithium chloride at moderate temperature. The synchrotron and neutron diffraction of the as-prepared O6-LiNi1/6Mn4/6O2 phase revealed an in-plane transition metal cation ordering in the (Li, Ni, Mn)O2 layers and only a moderate number of stacking faults along the c-axis direction in the oxygen stacking sequence. During the lithium electrochemical deintercalation and intercalation, both the in-plane metal transition ordering and the O6-type stacking are preserved and the lithium metal battery cells with the O6-LiNi1/6Mn4/6O2 phase as active material at the positive electrode show high (230 mA h g-1 for the first discharge) and relatively stable capacity with almost no voltage decay. This could be attributed to the environment surrounding the transition metal ions, which is more favorable for reversible migration of transition metal cations compared to the conventional O3-type lithium-rich layered oxides. All this indicates that O6-type lithium-rich layered oxides could be promising active materials for lithium-ion batteries. A cobalt-free manganese-based lithium-rich layered oxide with an unusual O6-type structure has been successfully synthesized by solid-state ion-exchange reaction from a P2-type sodium-based layered oxide precursor using LiCl at moderate temperature.

The prismatic environment of the alkali metal ion is demonstrated to control plateau hysteresis in lattice oxygen redox materials.

Nickel-rich layered oxides are adopted as electrode materials for EV's. They suffer from a capacity loss when the cells are charged above 4.15 V versus Li/Li+. Doping and coating can lead to significant improvement in cycling. However, the mechanisms involved at high voltage are not clear. This work is focused on LiNiO2 to overcome the effect of M cations. Galvanostatic intermittent titration technique (GITT) and in situ X-ray diffraction (XRD) experiments are performed at very low rates in various voltage ranges (3.8-4.3 V,). On the "4.2-4.3 V" plateau the R2 phase is transformed simultaneously in R3, R3 with H4 stacking faults and H4. As the charge proceeds above 4.17 V cell polarization increases, hindering Li deintercalation. In discharge, such polarization decreases immediately. Upon cycling, the polarization increases at each charge above 4.17 V. In discharge, the capacity and dQ/dV features below 4.1 V remain constant and unaffected, suggesting that the bulk of the material do not undergo significant structural defect. This study shows that the change in polarization results from the electrochemical behavior of the grain surface having very low conductivity above 4.17 V and high conductivity below this threshold. This new approach can explain the behavior observed with dopants like tungsten.

The rock-salt phase (RSP) formed on the surface of Ni-rich layered cathodes in liquid-electrolyte lithium-ion batteries is conceived to be electrochemically "dead". Here we show massive RSP forms in the interior of LiNixMnyCo(1−x-y)O2 (NMC) crystals in sulfide based all solid state batteries (ASSBs), but the RSP remains electrochemically active even after long cycles. The RSP and the layered structure constitute a two-phase mixture, a material architecture that is distinctly different from the RSP in liquid electrolytes. The tensioned layered phase affords an effective percolation channel into which lithium is squeezed out of the RSPs by compressive stress, rendering the RSPs electrochemically active. Consequently, the ASSBs with predominant RSP in the NMC cathode deliver remarkable long cycle life of 4000 cycles at high areal capacity of 4.3 mAh/cm2. Our study unveils distinct mechano-electrochemistry of RSPs in ASSBs that can be harnessed to enable high energy density and durable ASSBs.

Nickel-rich layered oxides Li(Ni,M)O2 (M = Co,Mn, ..) are widely adopted as electrode materials for electric vehicles. They suffer from a loss of capacity when the cells are charged above 4.15 V vs Li/Li+. This limitation is generally attributed to: (i) sharp decrease of the interslab distance at the end of charge which induces cracks in the particles, (ii) slab gliding leading to the formation of the H4 phase, (iii) reaction with the liquid electrolyte, which leads to formation of a rocksalt type structure. The cycling behavior can be improved by texture optimization (concentration gradient, structural orientation). Doping, coating with various cations lead, in some cases, to significant improvement of the cycling properties when the cells are cycled at high voltage. However, the true mechanisms involved at high voltage are not fully understood. In order to overcome the effect of M cations our work was focused on LiNiO2. GITT and in situ XRD experiments were performed at very low rate in various voltage range (3.8 -4.3 V). On the "4.2-4.3 V plateau" the R2 phase is transformed simultaneously in R3, R3 with H4 stacking faults and H4. When the cell voltage is extended to 4.6V the H4 phase (NiO2) is formed. Cells were charged up to 4.3, 4.5 and 4.6V with a long potentiostatic step (144 hours).The recovered materials were characterized by S-XRD and HAADF electron microscopy. In all cases a mixture of R3 and H4 phases were obtained. The electron microscopy show that both phase R3 an H4 are mixed inside the whole particles. NiO2 is expected to be an ionic insulator (no Li+) and an electronic insulator (d6 low spin). Since there is no formation of a shell of NiO2 around the particles, the difficulty to deintercalation Li suggests that at high voltage another mechanism must be considered. To try to have a better understanding of the involved process several electrochemical studies were performed in various experimental conditions. As the charge proceeds above 4.17 V the cell polarization dramatically increases, hindering further Li deintercalation. In discharge, such polarization decreases immediately. Also and upon cycling, the polarization increases at each charge above 4.17 V. In discharge, the capacity and dQ/dV features below 4.1 V remain constant and unaffected, suggesting that the bulk of the material did not undergo significant structural defect. This study shows that the change in polarization between the charge and the discharge results from the electrochemical behavior of the grain surface rocksalt type phase having very low conductivity above 4.17 V and high conductivity below this threshold. The results presented here open a new approach to monitor the electrochemical behavior of the rocksalt type shell and manage its electrochemical properties, at high voltage, by cationic doping of the surface layer. It can explain the behavior observed with some dopants (usually referred as “infused” coatings) like tungsten.

The metastable, O2-type cobalt-free lithium-rich layered oxide Li0.84Ni0.14Mn0.72O2 was successfully prepared by a new all-solid-state ion-exchange reaction from the P2-type sodium layered oxide precursor Na0.7[Li0.84Ni0.14Mn0.72]O-2 using lithium chloride at moderate temperature. The particular oxygen stacking in the resulting O2-type structure is assumed to suppress the detrimental layer-to-spinel phase transition usually observed upon cycling in conventional O3-type lithium-rich layered oxides due to the irreversible migration of transition metal cations, causing substantial voltage decay and capacity fading. Despite the existence of stacking faults originating from the P2-to-O2 topotactic reaction during the Na+-to-Li+ exchange, as evidenced by X-ray diffraction simulation and high-resolution microscopy, the electrochemical tests conducted on the faulted O2-type positive electrode material revealed a greatly improved reversible (de)intercalation mechanism along with high specific capacity values. An operando X-ray diffraction study indicated that there are only small structural changes upon cycling and that they are stable and reversible. Moreover, operando X-ray absorption spectroscopy experiments showed that a large part of the capacity relies on the oxygen redox, which is also reversible upon cycling.

P2-Na0.70CoO2 is considered as a model material for positive electrode applications in Na-ion batteries. In this study, we report an in-depth study and characterization of the P2-NaxCoO2 system in order to understand the material evolution from the point of view of the structure at different scales and electronic properties upon charge up to a high voltage (4.6 V). Using a combination of ex situ and operando X-ray diffraction (XRD) and ex situ 23Na magic-angle spinning nuclear magnetic resonance (MAS NMR), we discuss the structural changes occurring due to the deintercalation of Na+ ions from the interlayer slabs and the change in the electronic structure and magnetic properties. The XRD study allows discussing the general evolution in relation with previous studies. The novelty lies here in the observation for the first time of an ordered phase for x = 1/3 appearing above 4.3 V followed by a disordering in the slab stacking for higher voltages. The combination of the data obtained using different techniques allowed the interpretation of the NMR shift and shape evolution versus the Na content. This study reveals a complex behavior due to the presence of localized and delocalized electrons, whose relative proportions change versus Na content.

A X (M)O 2 layered oxides (A = Li, Na) are considered as the best positive electrode materials either for Li ion and Na ion batteries. In most of the systems, the shape of the voltage curve shows change in slope of the curve which indicate the occurrence of structural transitions due to: (i) electronic configuration modification in the MO 2 slab, (ii) change in the slab packing, (iii) alkali ion-vacancy ordering. Moreover, in A X (M,L)O 2 materials a M/L ordering can occur within the (M,L)O 2 slab for the pristine material. Lithium and sodium tends to be ordered in the deintercalated materials for peculiar compositions. Nevertheless, due to the larger ionic radii of Na + vs Li + , the repulsive interaction between sodium ions are stronger for sodium, leading to many Na + /vacancy patterns in the interslab space. Moreover, transition element orderings can occur within the (L,M)O 2 slab if the difference in size is significant and if the cation ratio corresponds to a specific composition (1/3, ½, 2/3...). Then an interesting behaviour is observed as the sodium/vacancy ordering in the interslab space can be st superimposed to the cation ordering. Another original situation is also observed for cations (d 2 or d 3 ) which like to form M-M bonds. In this case, the pattering of short bond and long bond in the MO 2 slab is directly related to the Na + /vacancy distribution and to the M 3+ /M 4+ ratio.

The effect of Al doping on the structure and electrochemical properties of LiCoO2 was investigated for a 4% doping amount, of practical interest for industrial application. Characterization of materials with low doping amount and precise control of the overall stoichiometry and homogeneity is challenging and could be performed in this study by combining 7Li, 27Al, 59Co nuclear magnetic resonance (NMR) and X-ray diffraction (XRD). 27Al magic angle spinning (MAS) NMR and XRD studies revealed that Al doping is homogeneous, and 7Li MAS NMR indicates that its stoichiometry (Li/M = 1.00) is ideal. The electrochemical tests have shown that Al doping improves the cycling stability at 4.6 V and strongly impacts the voltage curve profile up to 5 V. By an ex situ XRD study of electrochemically deintercalated LixCo0.96Al0.04O2 and LixCoO2 materials controlling the state of charge or the voltage, we showed that Al doping delays the formation of the H1-3 and O1 phases. Our 7Li MAS NMR and transmission electron microscopy (TEM) results revealed the formation of a lithiated spinel-type phase at the surface of the Al-doped electrode material, together with the formation of a stable cathode electrolyte interphase (CEI) layer unlike for LiCoO2. The different nature of the electrode/electrolyte interphases may therefore explain better the ionic/electronic conductivities of the Al-doped electrode and may hinder Co dissolution at a high voltage.

Manganese could be the element of choice for cathode materials used in large-scale energy storage systems owing to its abundance and low toxicity levels. However, both lithium- and sodium-ion batteries adopting this electrode chemistry suffer from rapid performance fading, suggesting a major technical barrier that must be overcome. Here we report a P3-type layered manganese oxide cathode Na0.6Li0.2Mn0.8O2 (NLMO) that delivers a high capacity of 240 mAh g−1 with outstanding cycling stability in a lithium half-cell. Combined experimental and theoretical characterizations reveal a characteristic topological feature that enables the good electrochemical performance. Specifically, the -α-γ- layer stack provides topological protection for lattice oxygen redox, whereas reversibility is absent in P2-structured NLMO, which takes an -α-β- configuration. The identified new order parameter opens an avenue towards the rational design of reversible Mn-rich cathode materials for sustainable batteries. Favoured cathodes for batteries should include abundant and redox-active elements, such as manganese. Here the authors report a Na0.6Li0.2Mn0.8O2 cathode design featuring a unique layer stacking sequence that provides topological protection to oxygen redox to overcome the performance fading.

This paper gives an overview of the research carried out on lithium and sodium layered materials as positive electrodes of lithium (sodium)‐ion batteries. It focuses on the solid‐state chemistry contribution to discover new materials and to optimize the properties versus the requirements imposed by the applications. Among, all material structures, which are considered, the layered ones (lithium based), are the best candidates for high energy density batteries for mobile applications. Recently, the homologous Na materials, which have lower energy, are considered for stationary applications due to their low price. Starting for LiMO 2 materials or Na x MO 2 (0.5 < x < 1), many substituted phases, obtained by high‐temperature solid‐state chemistry, have allowed stabilizing the layered structure in large composition domains to increase the specific capacity, which is directly related to the number of exchanged electrons during the cycling process.