Cationic Redox Research Articles

Dynamic Transition Metal Network via Orbital Population Design Stabilizes Lattice Oxygen Redox in Stoichiometric Layered Cathodes.

Li-ion batteries employing stoichiometric layered Li metal oxides as cathodes are now reaching the energy density limits due to single cationic redox chemistry. Lattice oxygen redox (LOR) has been discovered in these materials, as a high-energy-density paradigm observed in Li-rich materials. Nevertheless, the origin of this process is not understood, preventing the rational design of better cathode materials. Here, employing stoichiometric Ni-based cathodes, it is demonstrated that LOR originates from a dynamic transition metal (TM) network caused by ion migration during the electrochemical process. This network is confirmed to be ribbon through both ex- and in-situ STEM observations, facilitating reversible LOR. Finally, a t2g orbital population rule is proposed to guide the design of ordered TM networks, supported by calculated structures and the synthesized ordered TM oxides reported. This work explains the mechanism of LOR in stoichiometric layered cathode materials, and sets a promising direction for the design of high-energy-density cathodes through the regulation of TM ordering.

Impacts of distorted local chemical coordination on electrochemical performance in hydrated vanadium pentoxide

Modulating and elevating the operating voltage of a given cathode is a significant challenge to enhance the energy density of secondary batteries without sacrificing power output. The chemical coordination strongly influences the energy levels of d-orbitals of redox cations in cathode materials, which tie to their operating voltage. In contrast to concentrated studies on enhancing the specific capacity, in this study, we choose bi-layered hydrated vanadium pentoxide as the model to modulate the d-orbital energy levels through local chemical coordination manipulation, achieving a higher operating voltage in rechargeable aqueous zinc ion batteries. Here we show that, by employing X-ray absorption spectroscopy (XAS) and pair distribution function (PDF) techniques, we can analyze the distortion of [VO6] octahedra and extract chemical bond information, deciphering the correlation between the chemical coordination and operating voltage in cathode materials. The fundamentals could guide the designing and developing RAZIBs with higher energy and power density.

New Insights into Anionic Redox in P2-Type Oxide Cathodes for Sodium-Ion Batteries.

Manganese/nickel-based layered transition metal oxides have caught the attention of studies as promising cathodes for sodium-ion batteries (SIBs). It is reported that utilizing both cationic and anionic redox reactions is a promising method for higher energy density cathodes. However, the anionic redox reaction comes at the expense of irreversible oxygen release. Hence, a Li-Mg cosubstituted P2-Na0.67Li0.07Mg0.07Ni0.28Mn0.58O2 material with a honeycomb-ordered superstructure was designed. The Ni3+/Ni4+ redox couple and the anionic redox reaction are proven to have a competitive relationship. Density functional theory calculations reveal the effect of O 2p nonbonding states from Li and prove that Mg-O bonds can stabilize the Ni-O eg states. In situ electrochemical impedance spectroscopy measurements and galvanostatic charging/discharging derived dV/dQ, representing resistance changes with time, are obtained to reveal the mechanism of the anionic redox reaction. This study presents the effect and mechanism of the O 2p nonbonding state and Mg-O bonds of manganese/nickel-based layered oxides.

Elucidating the Limit of Lithium Difluorophosphate Electrolyte Additive for High‐Voltage Li/Mn‐Rich Layered Oxide || Graphite Li Ion Batteries

Li/Mn‐rich layered oxide (LMR) cathode active materials offer remarkably high specific discharge capacity (>250 mAh g−1) from both cationic and anionic redox. The latter necessitates harsh charging conditions to high cathode potentials (>4.5 V vs Li|Li+), which is accompanied by lattice oxygen release, phase transformation, voltage fade, and transition metal (TM) dissolution. In cells with graphite anode, TM dissolution is particularly detrimental as it initiates electrode crosstalk. Lithium difluorophosphate (LiDFP) is known for its pivotal role in suppressing electrode crosstalk through TM scavenging. In LMR || graphite cells charged to an upper cutoff voltage (UCV) of 4.5 V, effective TM scavenging effects of LiDFP are observed. In contrast, for an UCV of 4.7 V, the scavenging effects are limited due to more severe TM dissolution compared an UCV of 4.5 V. Given the saturation in solubility of the TM scavenging agents, which are LiDFP decomposition products, e.g., PO43− and PO3F2−, higher concentrations of the LiDFP as “precursor” cannot enhance the amount of scavenging species, they rather start to precipitate and damage the anode.

Cationic and Anionic Dual Redox Activity of MoS2 for Electrochemical Potassium Storage.

MoS2 is regarded as one of the most promising potassium-ion battery (PIB) anodes. Despite the great progress to enhance its electrochemical performance, understanding of the electrochemical mechanism to store K-ions in MoS2 remains unclear. This work reports that the K storage process in MoS2 follows a complex reaction pathway involving the conversion reactions of Mo and S, showing both cationic redox activity of Mo and anionic redox activity of S. The presence of dual redox activity, characterized in-depth through synchrotron X-ray absorption, X-ray photoelectron, Raman, and UV-vis spectroscopies, reveals that the irreversible Mo oxidation during the depotassiation process directs the reaction pathway toward S oxidation, which leads to the occurrence of K-S electrochemistry in the (de)potassiation process. Moreover, the dual reaction pathway can be adjusted by controlling the discharge depth at different cycling stages of MoS2, realizing a long-term stable cycle life of MoS2 as a PIB anode.

NaLiFe(C2O4)2: A polyanionic Li/Na-ion battery cathode exhibiting cationic and anionic redox

Recently, polyanionic compounds have received great interest as alternative cathode materials to conventional oxides due to their different advantages in cost, safety, structural stability, as well as being environmentally friendly. However, the vast majority of polyanionic materials reported so far rely exclusively upon the redox reaction of the transition metal for lithium/sodium transfer.The development of multielectron redox-active cathode materials is a top priority for achieving high energy density with long cycle life in the next-generation secondary battery applications. Triggering anion redox activity is a promising strategy to enhance the energy density of polyanionic cathode materials for Li/Na-ion batteries. In addition to transition metal redox activity, the oxalate group also shows redox behavior enabling reversible charge/discharge and high capacity without gas evolution.Herein, we report NaLiFe(C2O4)2 as a new positive electrode and use different characterization techniques such as Raman spectroscopy and Mössbauer analyses to characterise this dual-ion redox process experimentally. First-principles calculations also help to understand the interactions between the transition metal and the oxalate group as the main factor that modulates the cationic and polyanionic redox couples in these materials.

Local electronic structure modulation via S substitution enables fast-discharging capability for Li-rich Mn-based oxides cathodes

Anionic and cationic redox reaction contribute to the ultrahigh specific capacities of Li-rich Mn-based oxides cathodes (LMNC). However, the irreversible oxygen evolution and sluggish kinetics result in the continuous capacity decay and poor rate performance, which limited its application as cathode material in lithium-ion batteries. Herein, the local electronic structure of LMNC is appropriately modulated via S2− doping to alleviate oxygen release, stabilize the crystal structure stability, and facilitate Li+ diffusion via facile surface defect engineering. The effect of S2− doping site on the systematically energy is investigated by DFT. Under the guidance of this result, LNMC-S is prepared by co-precipitation and high-temperature solid-phase reaction method. The effect of doping concentration on electrochemical property of LMNC was systematically investigated. The results exhibit that S2− doping can effectively suppress the electronic insulation of Li2MnO3, enhance the transport dynamics of lithium ion and inhibit the phase transition of LMNC sample during charge-discharge process. Thereby, the modified sample exhibits superior electrochemical property, such as the 200th discharge capacity is 184.3 mAh·g−1 under 1C, with a capacity retention rate of 87.6 %. This paper is beneficial for enriching the existing theoretical findings and discoveries, providing theoretical guidance for the preparation of high-performance material.

Interlayer substitution enables air-stable and long-life O3-type cathode for sodium-ion batteries

The O3-type oxides (NaNi0.4Fe0.2Mn0.4O2 (NFM)) have been considered as the most commercially cathode material for high-energy-density sodium-ion batteries owing to their low price, good safety performance, and high energy density. However, their further development is seriously limited due to the complex phase transition, sluggish kinetics of Na+, and intrinsic air instability. Herein, an interlayer substituted NFM (IS-NFM) is constructed by a simple solid-state method with the introduction of alkaline-earth metal. The interlayer substitution will lead to the increase of oxygen content in the internal lattice, which will effectively suppress the irreversible phase transition during cycling and exposure to the air. In addition, the interlayer substitution effectively activated the charge compensation, leading to the mobilized cationic redox process and boosted de-/sodiated kinetic. Consequently, IS-NFM exhibits excellent capacity retention of 83.44 % at 1 C after 200 cycles and remarkable stability even at high voltage. After 15 days of exposure to the air, IS-NFM also delivers superior capacity retention (86.53 %, compared with 0.1 C) and cycling performance (82.70 % at 1 C after 200 cycles). Undoubtedly, the interlayer substitution strategy will expand a novel avenue for constructing air-stable and long-life O3-type oxides for commercial application.

Unraveling the Contribution of Cationic and Anionic Redox in Na-Rich Cathode Materials through First-Principles Calculations

Unraveling the Contribution of Cationic and Anionic Redox in Na-Rich Cathode Materials through First-Principles Calculations

Boosting cationic and anionic redox activity of Li-rich layered oxide cathodes via Li/Ni disordered regulation

Lithium-rich layered oxides (LLOs) are increasingly recognized as promising cathode materials for next-generation high-energy-density lithium-ion batteries (LIBs). However, they suffer from voltage decay and low initial Coulombic efficiency (ICE) due to severe structural degradation caused by irreversible O release. Herein, we introduce a three-in-one strategy of increasing Ni and Mn content, along with Li/Ni disordering and TM–O covalency regulation to boost cationic and anionic redox activity simultaneously and thus enhance the electrochemical activity of LLOs. The target material, Li1.2Ni0.168Mn0.558Co0.074O2 (L1), exhibits an improved ICE of 87.2% and specific capacity of 293.2 mA h g−1 and minimal voltage decay of less than 0.53 mV cycle−1 over 300 cycles at 1C, compared to Li1.2Ni0.13Mn0.54Co0.13O2 (Ls) (274.4 mA h g−1 for initial capacity, 73.8% for ICE and voltage decay of 0.84 mV/cycle over 300 cycles at 1C). Theoretical calculations reveal that the density of states (DOS) area near the Fermi energy level for L1 is larger than that of Ls, indicating higher anionic and cationic redox reactivity than Ls. Moreover, L1 exhibits increased O-vacancy formation energy due to higher Li/Ni disordering of 4.76% (quantified by X-ray diffraction Rietveld refinement) and enhanced TM–O covalency, making lattice O release more difficult and thus improving electrochemical stability. The increased Li/Ni disordering also leads to more Ni2+ presence in the Li layer, which acts as a pillar during Li+ de-embedding, improving structural stability. This research not only presents a viable approach to designing low-Co LLOs with enhanced capacity and ICE but also contributes significantly to the fundamental understanding of structural regulation in high-performance LIB cathodes.

Achieving Ultra-High-Energy-Density Lithium Batteries: Elimination of Irreversible Anionic Redox through Controlled Cationic Disordering.

Lithium-rich layered oxides (LLOs) capable of supporting both cationic and anionic redox chemistry are promising cathode materials. Yet, their initial charge to high voltages often trigger significant oxygen evolution, resulting in substantial capacity loss and structural instability. In this study, we applied a straightforward low-potential activation (LOWPA) method alongside a relatively stable electrolyte to address this issue. This approach enables precise control over the order-to-disorder transformation of the transition metal layers in LLOs, producing an in-plane cation-disordered Li1.2Mn0.54Co0.13Ni0.13O2 that averts irreversible oxygen evolution at 4.8 V by stabilizing Mn-O2 or Mn-O3 species within the Li/Mn-disordered nanopores. Consequently, an ultrahigh reversible capacity of 322 mAh g-1 (equating to 1141 Wh kg-1), 91.5% initial Coulombic efficiency, and enhanced durability and rate capability are simultaneously achieved. As LOWPA does not alter any chemical composition of LLOs, it also offers a simple model for untangling the complex phenomena associated with oxygen-redox chemistry.

Assessment of “Inverse” Cross‐Talk (Anode to Cathode) in High‐Voltage Li/Mn‐Rich Layered Oxide || Li Cells

AbstractLi/Mn‐rich layered oxide (LMR) offers high practical discharge capacity originating from both cationic and anionic redox, but its operation is practically challenging as full capacity utilization at high cathode potentials (> 4.6 V vs Li|Li+) is intertwined with phase transformation, oxygen release, and transition metal dissolution. Dissolved TMs in particular, can deposit and damage the anode via a process known as electrode cross‐talk that decreases Li inventory due to Li plating. Given the excess in active lithium, Li‐metal anode (LMA) is frequently paired with LMR for a systematic cathode R&D, though is believed to cause inverse cross‐talk, i.e., diffusion of LMA degradation products from the solid electrolyte interphase (SEI) toward the cathode, triggering bulid‐up of resistive cathode electrolyte interphase (CEI). Indeed, a thicker, more organic‐based, and slightly resistive CEI is proven in Li‐ compared to “SEI‐poor” Li4Ti5O12 (LTO)‐based cells via X‐ray photoelectron spectroscopy, time‐of‐flight secondary ion mass spectrometry, and electrochemical techniques, which likely even decreases metal dissolution from LMR, though their practical impact on overpotential is shown to be less relevant. The capacity recovery after transferring cycled (“old”) LMR from Li cells to fresh Li cells rather points to other meaningful contributions to capacity fading than the inverse crosstalk.

The Challenge of Polyanion Redox Process in Oxalates

Lately, polyanionic compounds have received great interest as alternative cathode materials to conventional oxides due to their different advantages in cost, safety, structural stability, as well as being environmentally friendly. However, the vast majority of polyanionic cathodes reported so far rely primarily upon the redox reaction of the transition metal for lithium/sodium transfer. The development of multielectron redox-active cathode materials is a top priority for achieving high energy density with long cycle life in the next-generation secondary battery applications. Triggering anion redox activity is considered to be a promising strategy to successfully enhance the energy density of polyanionic cathodes for Li/Na-ion batteries. In addition to transition metal redox activity, the oxalate group itself also shows redox behaviour enabling reversible charge/discharge and high capacity without gas evolution.Recently, our group reported dual ion redox in the lithium iron oxalate, in the potassium iron oxalate and in the sodium lithium iron oxalate, Li2Fe(C2O4)2, K2Fe(C2O4)2 & NaLiFe(C2O4)2 1 ,2,3 in which both the iron and the oxalate group appear to exhibit reversible redox activity. We also found this phenomenon present in the lithium-rich KLi3Fe(C2O4)3.4 Different characterisation techniques such as Raman spectroscopy or Synchrotron HAXPES and XAS analyses make it possible to show this phenomenon experimentally. First-principles calculations also help to understand the interactions between the transition metal and the oxalate group as the main factor that modulates the cationic and polyanionic redox couples in these materials.Our current results suggest that this phenomenon could be widespread among transition metal oxalates.Moreover, the oxalate anion is a particularly versatile species and may be monodentate, bidentate, tridentate, or even tetradentate, giving rise to a huge range of possible compounds and a very rich structural chemistry. It is important to establish the structural requirements that give rise to polyanion redox behaviour and a range of materials are being synthesised and characterised by our group. In addition to pure oxalates, it is possible to prepare materials with mixed polyanions e.g., oxalate/phosphate.In our work, we demonstrate that oxalate has a role as a family of cathode materials and suggests a direction for the identification and design of electrode materials with polyanionic frameworks.(1) Yao, W.; Armstrong, A. R.; Zhou, X.; Sougrati, M. T.; Kidkhunthod, P.; Tunmee, S.; Sun, C.; Sattayaporn, S.; Lightfoot, P.; Ji, B.; Jiang, C.; Wu, N.; Tang, Y.; Cheng, H. M. An Oxalate Cathode for Lithium Ion Batteries with Combined Cationic and Polyanionic Redox. Nat. Commun. 2019, 10 (1), 1–9.(2) Pramanik, A.; Manche, A. G.; Sougrati, M. T.; Chadwick, A. G.; Lightfoot, P.; Armstrong, A. R. K2Fe(C2O4)2: a New Oxalate Cathode for Li/Na ion Batteries Exhibiting a Combination of Multielectron Cation and Anion Redox. Chem.of Mat. 2023, 35, 2600–2611.(3) Manche, A. G.; Pramanik, A.; Lindgren, F.; Ericsson, T.; Häggström, L.; Armstrong, A. R. NaLiFe(C2O4)2: A New Iron-Based Polyanionic Cathode for Next-Generation Li/Na-ion Battery Exhibiting Reversible Cationic and Anionic Redox Behaviour. Energy Storage Mat. 2024, In review (4) Pramanik, A.; Manche, A. G.; Clulow, R.; Lightfoot, P.; Armstrong, A. R. Exploiting Anion and Cation Redox Chemistry in Lithium-Rich Perovskite Oxalate: A Novel next-Generation Li/Na-Ion Battery Electrode. Dalt. Trans. 2022, 51 (33), 12467–12475.

Accessing Cation and Anion Redox in a 1-D Iron-Chalcogenide, Na3Fe2S4-XSex (x = 0, 2, & 4), in Na-Ion Batteries

The utilization of anionic redox activity is gaining significant interest in chalcogen based alkali-ion batteries. In this study, we are reporting reversible Na-ion (de)intercalation in one-dimensional structure of Na3Fe2S4-xSex (x = 0, 2, and 4). The crystal structure of Na3Fe0.5 2+Fe0.5 3+Q4 (Q = S and Se) can be visualized as a mixed valent iron, Fe2+/Fe3+ , forming infinite edge-shared chain of FeQ 4 tetrahedra with Na-ion residing in the interchain voids. While cycling the cathodes within a potential range of 1.5 – 2.5 V vs. Na/Na+, we could reversibly (de)intercalate one mole of Na from the structure. Mössbauer spectroscopy reveals a complete Fe2+ to Fe3+ oxidation in all the charged samples. Substitution of less electronegative Se2– in the structure systematically lowers the Fe2+/3+ redox couple during cycling. After 100 cycles at 1C rate, the cathode retains 83 % of its initial reversible capacity. While cycling the same cathode at a higher voltage range of 1.5 – 3.0 V, we observed a flat plateau profile at ~2.6 V with capacity reaching 255 mAh/g for Na3Fe2S4 cathode. This high capacity can be directly attributed to the anion oxidation for the charge compensation process during ~3.0 Na-ion deintercalation as supported by XPS analysis. The flat plateau profile further decreases from 2.6 to 2.5 V with the substitution of Se2–. The GITT results show two distinct kinetic behavior for the cation (fast) and anion (sluggish) redox. The decoupling of cation and anion redox in this system can enable us to understand and optimize the utilization of both redox chemistries to achieve a high energy density cathode.

Towards the Direct Observation of the Local and Electronic Structure Evolution of Positive Electrode Materials by X-Ray Raman Scattering and X-Ray Emission Spectroscopy

The emergence of high brilliance synchrotron sources and the availability of more sophisticated infrastructure have opened doors to advanced material characterization, enabling a profound understanding of new processes and mechanisms in battery research. [1] More specifically, non-resonant Valence-to-Core X-ray emission spectroscopy (VtC-XES) and X-ray Raman scattering (XRS) stand out as complementary photon-in/photon-out X-ray spectroscopy techniques. The unique capability of these techniques lies in their access to soft X-ray edges using a hard X-ray beam, providing comprehensive information on both the electronic and local structure, due to their high sensitivity to local structure and coordination. [2,3] In this work, two different families of materials with different compositions and crystal structures are studied using XES and XRS.The first part focuses on the detailed study of oxygen substituted KVPO4F1-xOx (x = 0, 0.25, 0.5, 0.75, 1) using VtC-XES combined to ab initio theoretical calculations. The average working potential increases with increasing oxygen content by activating the V3+/4+ and V4+/5+ redox couples and replacing the VO4F2 “ionic” entity by {V=O}O5 unit with a highly “covalent” vanadyl-type bond. [4] VtC-XES allowed us to distinguish the contributions of V-F, V-O, and V=O bonds in the local environment, with spectral intensities highly correlated to the F- and O2- anionic composition. In addition, specific spectral evolutions are also associated to the presence of highly covalent V=O bonds, strongly influencing the electrode potential of the material.The second part examines a series of electrochemically obtained LiyNiO2 layered oxide materials (y = 0.02, 0.25, 0.33, 0.5, 0.67, 1.0). VtC-XES performed at the Ni Kβ emission line allows to study the local structure evolution around Ni, whereas XRS spectroscopy at both the O K-edge and Ni L2,3 L-edges gives an access to the interplay between Ni and O through the hybridized states of Ni 3d and O 2p. [5] This work provides a survey on both the cationic and anionic redox processes, and unveils the underlying phenomena related to the charge compensation processes occurring in this material.Overall, we present a comprehensive study of different polyanionic and layered oxide positive electrode materials using complementary X-ray spectroscopic techniques to probe both the local and electronic structures. We demonstrate that they allow to follow and understand evolution and changes in the local structure in materials of intricate crystal structures.AcknowledgementThis work was supported by the DESTINY Marie Skłodowska-Curie Actions COFUND PhD Programme (Grant Agreement #945357) co-funded by the European Union's Horizon2020 research and innovation program and the Synchrotron SOLEIL. ANR is also acknowledged for funding the RS2E network through the STORE-EX Labex Project ANR-10-LABX-76-01. Alistore-ERI network is also acknowledged.

Induced Anion Redox before Full Oxidation of Ru4+/Ru5+ through Local Configuration Modulation in P2-Na0.67[Mg0.33Ru0.67]O2

The study of anionic redox in layered-oxide cathodes for Na-ion batteries (NIBs) has been extensive, aiming to attain high-energy density. The involvement of Mn4+ or Ru5+ oxidation states is known to be crucial for the anionic O2 −/O− reaction during Na+ de/intercalation. Nevertheless, our findings indicate that anionic redox can activate in Ru-based layered-oxide cathodes prior to complete Ru4+/Ru5+ oxidation. By employing first-principles calculation and experimental techniques, we disclose that additional Na+ deintercalation from P2-Na0.33[Mg0.33Ru0.67]O2 relies on anionic oxidation after extracting 0.33 mol Na+ from P2-Na0.67[Mg0.33Ru0.67]O2, concomitant with cationic oxidation of Ru4+/Ru4.5+. Specifically, only the oxygen adjacent to 2Mg/1Ru is implicated in anionic redox during Na+ de/intercalation, indicating that the Na–O–Mg arrangement in the P2-Na0.33[Mg0.33Ru0.67]O2 structure significantly reduces the thermodynamic stability of anionic redox compared to cationic redox. Through O anionic and Ru cationic reactions, P2-Na0.67[Mg0.33Ru0.67]O2 demonstrates a substantial specific capacity of ∼172 mA h g− 1 and exceptional power capability, facilitated by facile Na+ diffusion and reversible structural changes during charge/discharge. These findings propose an innovative strategy to enhance anionic redox activity by modifying the local oxygen environment, paving the way for high-energy-density cathode materials in NIBs.

High Areal Capacity Cation and Anionic Redox Solid-State Batteries Enabled by Transition Metal Sulfide Conversion.

Pure sulfur (S8 and Li2S) all solid-state batteries inherently suffer from low electronic conductivities, requiring the use of carbon additives, resulting in decreased active material loading at the expense of increased loading of the passive components. In this work, a transition metal sulfide in combination with lithium disulfide is employed as a dual cation-anion redox conversion composite cathode system. The transition metal sulfide undergoes cation redox, enhancing the electronic conductivity, whereas the lithium disulfide undergoes anion redox, enabling high-voltage redox conducive to achieving high energy densities. Carbon-free cathode composites with active material loadings above 6.0 mg cm-2 attaining areal capacities of ∼4 mAh cm-2 are demonstrated with the possibility to further increase the active mass loading above 10 mg cm-2 achieving cathode areal capacities above 6 mAh cm-2, albeit with less cycle stability. In addition, the effective partial transport and thermal properties of the composites are investigated to better understand FeS:Li2S cathode properties at the composite level. The work introduced here provides an alternative route and blueprint toward designing new dual conversion cathode systems, which can operate without carbon additives enabling higher active material loadings and areal capacities.

Cation-disordered Li2FeTiO4 nanoparticles with multiple cation and anion redox for symmetric lithium-ion batteries

Cation-disordered Li2FeTiO4 nanoparticles with multiple cation and anion redox for symmetric lithium-ion batteries

Separating Cationic and Anionic Redox Activity in the Lithium-Rich Antiperovskite (Li2Fe)SO.

Lithium-rich antiperovskites promise to be a compelling class of high-capacity cathode materials due to the existence of both cationic and anionic redox activity. Little is however known about the effect of separating the electrochemical cationic process from the anionic process and the associated implications on the electrochemical performance. In this context, we report the electrochemical properties of the illustrative example of three different (Li2Fe)SO materials with a focus on separating cationic from anionic effects. With the high-voltage anionic process, an astonishing electrochemical capacity of around 400 mAh g-1 can initially be reached. Our results however identify the anionic process as the cause of poor cycling stability and demonstrate that the fading reported in previous literature is avoided by restricting to only the cationic processes. Following this path, our (Li2Fe)SO-BM500 shows strongly improved performance as indicated by constant electrochemical cycling over 100 cycles at a capacity of around 175 mAh g-1 at 1 C. Our approach also allows us to investigate the electrochemical performance of the bare antiperovskite phase excluding extrinsic activity from initial or cycling-induced impurity phases. Our results underscore that synthesis conditions are a critical determinant of electrochemical performance in lithium-rich antiperovskites, especially with regard to the amount of electrochemical secondary phases, while the particle size has not been found to be a crucial parameter. Overall, separating and understanding the effects of the cationic from the anionic redox activity in lithium-rich antiperovskites provides the route to further improve their performance in electrochemical energy storage.

Recent Advances in Oxygen Redox Activity of Lithium‐Rich Manganese‐Based Layered Oxides Cathode Materials: Mechanism, Challenges and Strategies

AbstractLithium‐rich manganese‐based layered oxides (LRMOs) have been regarded as a promising category of cathode materials due to their high specific capacity on basis of joint anionic(oxygen) /cationic redox chemistry at a high voltage, thus high energy density. The anionic redox play the key and restive roles in LRMOs, contributing the extra capacity, meanwhile being associated with several unfavorable structural and electrochemical issues. This work systematically enumerates the oxygen redox mechanisms, and challenges associated with oxygen‐anion redox in LRMOs, including irreversible transition metal migration, phase transition, and the capacity/voltage decay, etc. The recent progress made in modification of LRMOs with particular emphasis to promoting the reversible oxygen redox reaction and inhibiting the irreversible oxygen release are summarized, followed by an outlook on the future rational design and development of LRMOs. This comprehensive review and perspective are expected to provide insights for the greater utilization of oxygen redox in LRMOs and other related materials.