Manganese-rich Layered Oxides Research Articles

Controlling Surface Structure and Primary Particle Size to Enhance Performance and Reduce Gas Evolution in Lithium- and Manganese-Rich Layered Oxide Cathodes.

Practical application of lithium- and manganese-rich layered oxide cathodes has been hindered despite their high performance and low cost owing to high gas evolution accompanying capacity loss even in a conservative voltage window. Here, we control the surface structure and primary particle size of lithium- and manganese-rich layered oxide cathodes not only to enhance the electrochemical performance but also to reduce gas evolution. Sulfur-coated Fm3̅m/R3̅m double reduced surface layers and Mo doping dramatically reduce gas evolution, which entails the improvement of electrochemical performance. With the optimization, we prove that it is competitive enough to conventional high-nickel cathodes in the aspects of gas evolution as well as electrochemical performance in the conservative voltage window of 2.5-4.4 V. Our findings provide invaluable insights on the improvement of electrochemical performance and gas evolution properties in lithium- and manganese-rich layered oxide cathodes.

Fluorination Effect on Lithium- and Manganese-Rich Layered Oxide Cathodes.

Lithium- and manganese-rich (LMR) layered oxides are promising high-energy cathodes for next-generation lithium-ion batteries, yet their commercialization has been hindered by a number of performance issues. While fluorination has been explored as a mitigating approach, results from polycrystalline-particle-based studies are inconsistent and the mechanism for improvement in some reports remains unclear. In the present study, we develop an in situ fluorination method that leads to fluorinated LMR with no apparent impurities. Using well-defined single-crystal Li1.2Ni0.2Mn0.6O2 (LNMO) as a platform, we show that a high fluorination level leads to decreased oxygen activities, reduced side reactions at high voltages, and a broadly improved cathode performance. Detailed characterization reveals a particle-level Mn3+ concentration gradient from the surface to the bulk of fluorinated-LNMO crystals, ascribed to the formation of a Ni-rich LizNixMn2-xO4-yFy (x > 0.5) spinel phase on the surface and a "spinel-layered" coherent structure in the bulk where domains of a LiNi0.5Mn1.5O4 high-voltage spinel phase are integrated into the native layered framework. This work provides fundamental understanding of the fluorination effect on LMR and key insights for future development of high-energy Mn-based cathodes with an intergrown/composite crystal structure.

Efficient direct repairing of lithium- and manganese-rich cathodes by concentrated solar radiation

Lithium- and manganese-rich layered oxide cathode materials have attracted extensive interest because of their high energy density. However, the rapid capacity fading and serve voltage decay over cycling make the waste management and recycling of key components indispensable. Herein, we report a facile concentrated solar radiation strategy for the direct recycling of Lithium- and manganese-rich cathodes, which enables the recovery of capacity and effectively improves its electrochemical stability. The phase change from layered to spinel on the particle surface and metastable state structure of cycled material provides the precondition for photocatalytic reaction and thermal reconstruction during concentrated solar radiation processing. The inducement of partial inverse spinel phase is identified after concentrated solar radiation treatment, which strongly enhances the redox activity of transition metal cations and oxygen anion, and reversibility of lattice structure. This study sheds new light on the reparation of spent cathode materials and designing high-performance compositions to mitigate structural degradation.

Tailored solution combustion method for enhancing high voltage electrochemical performance Li1.2Ni0.1Mn0.6Co0.1O2 as cathode material for lithium-ion batteries

The Lithium and Manganese-rich layered oxides with the formula Li1.2Ni0.1Mn0.6Co0.1O2 (LMR-NMC) are considered the most promising cathode materials for next-generation lithium-ion batteries due to their high energy densities, low cost, high thermal stability, and environmental safety. This paper reports the synthesis of LMR-NMC oxides in the presence of glycine-urea or citric acid-urea as surface modifiers for LMR-NMC-A and LMR-NMC-B, respectively using the solution combustion technique. The crystal structures of LMR-NMC-A and LMR-NMC-B samples were confirmed to have Hexagonal α-NaFeO2 structures in the R-3m space group. The HRSEM images reveal two different morphologies of the samples; Nano platelet (LMR-NMC-A) and Cubic-like (LMR-NMC-B). The cyclic voltammetric studies (CV) performed at a low scan rate value of 0.1 mV s−1 and a potential window of 2.0–5.0 V confirm the formation of the irreversible Li2MnO3 phase above 4.8 V in the first cycle and the presence of three redox peaks corresponding to Ni2+/Ni4+, Co2+/Co3+, and Mn3+/Mn in the subsequent cycles. The electrochemical properties of LMR-NMC-A and LMR-NMC-B electrodes demonstrated an initial discharge-specific capacity of 325.21 mAh g−1 and 300 mAh g−1, respectively, in a potential range between 2.0 and 5.0 V at a 0.1C rate. A comparison of the electrochemical properties of both morphologies of LMR-NMC revealed that the Nanoplatelet-like (LMR-NMC-A) sample performs better than the cubic-like (LMR-NMC-B) sample. The Nanoplatelet-like layered oxide demonstrated a high specific capacity of 180 mAh g−1 at a 1C rate and a high Coulombic efficiency of 86% after 200 cycles. BET indicates that LMR-NMC-A has a significantly higher surface area and substantial pore volume than LMR-NMC-B, addressing high voltage working capability, low voltage fading, and high specific capacitance values to a greater extent. These findings confirm the suitability of LMR-NMC-A as a cathode material for lithium-ion batteries used in high-load appliances and heavy vehicles.

Heat Generation during the First Activation Cycle of Li-Ion Batteries with Li- and Mn-Rich Layered Oxides Measured by Isothermal Micro-Calorimetry

Using isothermal micro-calorimetry, we investigate the heat generation of lithium- and manganese-rich layered oxides (LMR-NCMs) during the first cycle in which LMR-NCM exhibits a pronounced voltage hysteresis leading to a low energy efficiency (≈73%). In the first charge, LMR-NCM shows a unique voltage plateau at ≈4.5 V where irreversible structural rearrangements lead to an activation of the material as well as a large voltage hysteresis. We found that only a fraction of the lost electrical work (≈43%) is converted into waste heat. Thereby, the heat flow profile of the first charge is unique and shows considerable heat generation during the voltage plateau. With complementary electrochemical methods, contributions of conventional sources of heat, i.e., because of polarization and entropy, are determined. However, they do not cause the considerable generation of heat during the voltage plateau. Our results therefore suggest that the structural rearrangements during activation lead to a significant generation of heat. In window-opening experiments, we demonstrate that the activation is a gradual process and that the heat generated during the first discharge is directly linked to the extent of activation during the preceding charge. We also investigate the effect of the degree of overlithiation on the heat generated during activation.

Annealing in Argon Universally Upgrades the Na-Storage Performance of Mn-Based Layered Oxide Cathodes by Creating Bulk Oxygen Vacancies.

Manganese-rich layered oxide cathodes of sodium-ion batteries (SIBs) are extremely promising for large-scale energy storage owing to their high capacities and cost effectiveness, while the Jahn-Teller (J-T) distortion and low operating potential of Mn redox largely hinder their practical applications. Herein, we reveal that annealing in argon rather than conventional air is a universal strategy to comprehensively upgrade the Na-storage performance of Mn-based oxide cathodes. Bulk oxygen vacancies are introduced via this method, leading to reduced Mn valence, lowered Mn 3d-orbital energy level, and formation of the new-concept Mn domains. As a result, the energy density of the model P2-Na0.75 Mg0.25 Mn0.75 O2 cathode increases by ≈50 % benefiting from the improved specific capacity and operating potential of Mn redox. The Mn domains can disrupt the cooperative J-T distortion, greatly promoting the cycling stability. This exciting finding opens a new avenue towards high-performance Mn-based oxide cathodes for SIBs.

(Invited, Digital Presentation) Design of New Cathodes for Sodium-Ion Batteries Harnessing Anionic Redox Activity: Two Case Studies

Sodium-ion batteries (SIBs) are widely pursued as pragmatic alternative to the Li-ion battery technology having close operational similarity along with natural resource abundance. In this sector, apart from classical cationic redox-based cathodes, various new cathodes have been unveiled based on anionic (oxygen) redox activity. In this work, we will showcase two such case studies of novel cathode composition for SIBs exploiting anionic redox activity.(1) P2-type manganese-rich layered oxides offers high capacity along with fast rate kinetics. To improve their electrochemical properties, reduce voltage decay upon cycling and to mitigate irreversible phase transitions, cation doping or hybrid composite integrations can be explored. We have tested a unique Mn-rich layer-spinel composite, Na0.7(Li1/18Mn11/18Ni3/18Fe2/181 /18)O2–xNa2MoO4, leading to a synergistic effect of layered P2 and spinel phases. This layer/spinel biphasic composite was stabilised through Mo doping and its electrochemical activity was studied at different voltage windows. Upon cycling between 1.5–4.5 V, this Mo-based composite exhibited a high specific capacity of 183 mAh.g-1 involving both cationic and anionic (O2-/O2 n-) redox activity. The structural evolution during (dis)charge was studied by ex-situ X-ray diffraction and cyclic voltammetry. It is observed that mitigating P2-P2´´ phase transition at higher voltage is crucial to improve the electrochemical performance, cycling stability and reduce the voltage hysteresis. The structural and electrochemical properties of this new composite cathode will be described (Fig. a) (manuscript submitted).(2) The second part will dwell on anionic redox activity of Na-based mixed-metal oxide cathode [Na0.7Mn0.6Ni0.3Co0.1O2]. Combining cationic and anionic redox activity, it exhibited a reversible capacity of 120 mAh/g with anionic redox activity centered around 4.3 V (Fig. b). The underlying redox mechanism has been investigated using in-situ XRD and Raman spectroscopy showing peroxo bond formation (Fig. c). The structural and electrochemical properties of this new cathode composition will be explained (manuscript submitted). Figure 1

NaxMnyNi1-YO2 Cathode Materials for Sodium-Ion Batteries: Structure, Synthesis, Electrochemistry and Influence of Ambient Storage

Expanding energy generation from renewables is inevitable to reduce the impact of man-made climate change. With that, the need for intermediate energy storage is gaining in significance. Today, lithium-ion batteries (LIBs) are dominating mobile drive-trains and also play a key role in stationary energy storage. LIBs are incorporating critical raw materials in view of availability and economic importance, such as cobalt, lithium, copper and graphite.Sodium-based batteries, in which sodium replaces lithium as ionic charge-carrier, utilize the same working principles but substitute critical raw materials for abundant and cost-effective alternatives. Hard carbon replaces graphite as anode active material, copper foils are substituted by aluminum current collectors and manganese-based cobalt-free layered host lattices offer promising performance as cathode active material 1,2. By applying established production processes, investment costs are reduced and a rapid scale-up is enabled (Drop-In technology) 3, making SIBs a sustainable, efficient and cost-effective complementary technology to LIBs 4.Among various known cathode active materials for SIBs, the family of layered sodium transition metal oxides (NaxMO2, 1>x>0) offers promising electrochemical performance 2,5–7. These compounds show a wide structural variety (O3, P3, P2) due to the ionic radius of sodium and the tendency for Na+/vacancy ordering 8.The scope of our presentation will be low-cost manganese-based, cobalt-free layered NaxMnyNi1-yO2 cathode active materials for SIBs. We will discuss the influence of the transition metal stoichiometry y on the structure based on Neutron and X-ray diffraction experiments. Using advanced electrochemical methods and diffraction experiments, these structural models are then correlated with physical and electrochemical properties such as Na+/vacancy orderings, solid diffusion coefficients and potential profiles. For y = 3/4, a synthesis phase diagram will be presented covering a broad range of sodium content x and calcination temperature. For phase-pure P2-NaxMn3/4Ni1/4O2, we will present the influence of the calcination process on the structure and discuss the electrochemical properties in half-cells in-depth. For optimized materials, attractive initial specific discharge capacities beyond 220 mAh g-1 are obtained in sodium half-cells between 1.5 – 4.3 V. A capacity decay occurs during electrochemical cycling within this full voltage window. The origin of the capacity decay will be discussed based on electrochemical studies and ex-situ investigations of the morphology with SEM and local structure with HRTEM. Finally, we will present the influence of storage in ambient air to gain insights on the large-scale processability of the materials.The chosen synthesis route adapts industrially established processes for NCM production for SIB cathode materials, enables to tune powder properties to technical specifications and is highly scalable. The broad scope of this work addresses raw material questions, fundamental investigations and industrially relevant production processes.ACKNOWLEDMENTS:The German Federal Ministry of Education and Research (BMBF) supported this work within the project TRANSITION (03XP0186C) and ExcellBattMat (03XP0257A and 03XP0257C).REFERENCES Larcher, D. & Tarascon, J.-M. Towards greener and more sustainable batteries for electrical energy storage. Nature Chem 7, 19–29; 10.1038/nchem.2085 (2015).Hasa, I. et al. Challenges of today for Na-based batteries of the future: From materials to cell metrics. Journal of Power Sources 482, 228872; 10.1016/j.jpowsour.2020.228872 (2021).Tarascon, J.-M. Na-ion versus Li-ion Batteries: Complementarity Rather than Competitiveness. Joule 4, 1616–1620; 10.1016/j.joule.2020.06.003 (2020).Vaalma, C., Buchholz, D., Weil, M. & Passerini, S. A cost and resource analysis of sodium-ion batteries. Nat Rev Mater 3, 1–11; 10.1038/natrevmats.2018.13 (2018).Nagore Ortiz-Vitoriano, Nicholas E. Drewett, Elena Gonzalo & Teófilo Rojo. High performance manganese-based layered oxide cathodes: overcoming the challenges of sodium ion batteries. Energy Environ. Sci. 10, 1051–1074; 10.1039/C7EE00566K (2017).Nuria Tapia-Ruiz et al. 2021 roadmap for sodium-ion batteries. J. Phys. Energy 3, 31503; 10.1088/2515-7655/ac01ef (2021).Gonzalo, E., Zarrabeitia, M., Drewett, N. E., López del Amo, Juan Miguel & Rojo, T. Sodium manganese-rich layered oxides: Potential candidates as positive electrode for Sodium-ion batteries. Energy Storage Materials 34, 682–707; 10.1016/j.ensm.2020.10.010 (2021).Kubota, K., Kumakura, S., Yoda, Y., Kuroki, K. & Komaba, S. Electrochemistry and Solid‐State Chemistry of NaMeO 2 (Me = 3d Transition Metals). Adv. Energy Mater. 8, 1703415; 10.1002/aenm.201703415 (2018).

A molybdenum doped layer-spinel composite cathode material for sodium-ion battery

Sodium-ion batteries are pursued as pragmatic alternative to the Li-ion battery technology having operational similarity along with natural resource abundance. P2-type manganese-rich layered oxides are widely explored exhibiting high capacity along with fast rate kinetics. To improve their electrochemical performance and reduce voltage decay upon cycling and to mitigate irreversible phase transitions, cation doping or hybrid composite integrations have been proposed. Here, we report a unique Mn-rich layer-spinel composite, Na0.7(Li1/18Mn11/18Ni3/18Fe2/18χ1/18)O2–xNa2MoO4, leading to a synergistic effect of layered P2 and spinel phases. This stable layer/spinel biphasic composite was stabilized through Mo doping and its electrochemical activity was studied at different voltage windows. When cycled between 1.5–4.5 V, this composite delivered a high specific capacity of 183 mAh.g–1 involving both cationic and anionic (O2–/O2n–) redox. The structural evolution during (dis)charge was studied by ex-situ X-ray diffraction and cyclic voltammetry. It is observed that mitigating P2-P2′′ phase transition at higher voltage is crucial to improve the electrochemical performance, cycling stability and reduce the voltage hysteresis.

Structural Origin of Suppressed Voltage Decay in Single-Crystalline Li-Rich Layered Li[Li0.2 Ni0.2 Mn0.6 ]O2 Cathodes.

Lithium- and manganese-rich layered oxides (LMLOs, ≥ 250 mAh g-1 ) with polycrystalline morphology always suffer from severe voltage decay upon cycling because of the anisotropic lattice strain and oxygen release induced chemo-mechanical breakdown. Herein, a Co-free single-crystalline LMLO, that is, Li[Li0.2 Ni0.2 Mn0.6 ]O2 (LLNMO-SC), is prepared via a Li+ /Na+ ion-exchange reaction. In situ synchrotron-based X-ray diffraction (sXRD) results demonstrate that relatively small changes in lattice parameters and reduced average micro-strain are observed in LLNMO-SC compared to its polycrystalline counterpart (LLNMO-PC) during the charge-discharge process. Specifically, the as-synthesized LLNMO-SC exhibits a unit cell volume change as low as 1.1% during electrochemical cycling. Such low strain characteristics ensure a stable framework for Li-ion insertion/extraction, which considerably enhances the structural stability of LLNMO during long-term cycling. Due to these peculiar benefits, the average discharge voltage of LLNMO-SC decreases by only ≈0.2V after 100 cycles at 28mA g-1 between 2.0 and 4.8V, which is much lower than that of LLNMO-PC (≈0.5V). Such a single-crystalline strategy offers a promising solution to constructing stable high-energy lithium-ion batteries (LIBs).

Entropy and crystal-facet modulation of P2-type layered cathodes for long-lasting sodium-based batteries

P2-type sodium manganese-rich layered oxides are promising cathode candidates for sodium-based batteries because of their appealing cost-effective and capacity features. However, the structural distortion and cationic rearrangement induced by irreversible phase transition and anionic redox reaction at high cell voltage (i.e., >4.0 V) cause sluggish Na-ion kinetics and severe capacity decay. To circumvent these issues, here, we report a strategy to develop P2-type layered cathodes via configurational entropy and ion-diffusion structural tuning. In situ synchrotron X-ray diffraction combined with electrochemical kinetic tests and microstructural characterizations reveal that the entropy-tuned Na0.62Mn0.67Ni0.23Cu0.05Mg0.07Ti0.01O2 (CuMgTi-571) cathode possesses more {010} active facet, improved structural and thermal stability and faster anionic redox kinetics compared to Na0.62Mn0.67Ni0.37O2. When tested in combination with a Na metal anode and a non-aqueous NaClO4-based electrolyte solution in coin cell configuration, the CuMgTi-571-based positive electrode enables an 87% capacity retention after 500 cycles at 120 mA g−1 and about 75% capacity retention after 2000 cycles at 1.2 A g−1.

Reaction inhomogeneity coupling with metal rearrangement triggers electrochemical degradation in lithium-rich layered cathode

High-energy density lithium-rich layered oxides are among the most promising candidates for next-generation energy storage. Unfortunately, these materials suffer from severe electrochemical degradation that includes capacity loss and voltage decay during long-term cycling. Present research efforts are primarily focused on understanding voltage decay phenomena while origins for capacity degradation have been largely ignored. Here, we thoroughly investigate causes for electrochemical performance decline with an emphasis on capacity loss in the lithium-rich layered oxides, as well as reaction pathways and kinetics. Advanced synchrotron-based X-ray two-dimensional and three-dimensional imaging techniques are combined with spectroscopic and scattering techniques to spatially visualize the reactivity at multiple length-scales on lithium- and manganese-rich layered oxides. These methods provide direct evidence for inhomogeneous manganese reactivity and ionic nickel rearrangement. Coupling deactivated manganese with nickel migration provides sluggish reaction kinetics and induces serious structural instability in the material. Our findings provide new insights and further understanding of electrochemical degradation, which serve to facilitate cathode material design improvements.

Phosphorus-doped lithium- and manganese-rich layered oxide cathode material for fast charging lithium-ion batteries

Owing to their high theoretical specific capacity and low cost, lithium- and manganese-rich layered oxide (LMR) cathode materials are receiving increasing attention for application in lithium-ion batteries. However, poor lithium ion and electron transport kinetics plus side effects of anion and cation redox reactions hamper power performance and stability of the LMRs. In this study, LMR Li1.2Mn0.6Ni0.2O2 was modified by phosphorus (P)-doping to increase Li+ conductivity in the bulk material. This was achieved by increasing the interlayer spacing of the lithium layer, electron transport and structural stability, resulting in improvement of the rate and safety performance. P5+ doping increased the distance between the (003) crystal planes from ~0.474 nm to 0.488 nm and enhanced the structural stability by forming strong covalent bonds with oxygen atoms, resulting in an improved rate performance (capacity retention from 38% to 50% at 0.05 C to 5 C) and thermal stability (50% heat release compared with pristine material). First-principles calculations showed the P-doping makes the transfer of excited electrons from the valence band to conduction band easier and P can form a strong covalent bond helping to stabilize material structure. Furthermore, the solid-state electrolyte modified P5+ doped LMR showed an improved cycle performance for up to 200 cycles with capacity retention of 90.5% and enhanced initial coulombic efficiency from 68.5% (pristine) or 81.7% (P-doped LMR) to 88.7%.

Phosphoric acid and thermal treatments reveal the peculiar role of surface oxygen anions in lithium and manganese-rich layered oxides

The peculiar role of surface oxygen anions and surface reconstruction in Co-free layered Li[Li0.2Ni0.2Mn0.6]O2 is discovered by dilute phosphoric acid and thermal treatments.

(Invited) Exploring Sodium Layered Oxide Cathodes: Designing Tailored Materials

Interest in developing energy storage systems to meet a wide array of future challenges has driven research into a range of new battery technologies. Sodium-ion batteries (SIBs) have proven to be particularly popular due to their attractive properties and broad range of potential applications. However, before SIBs take their place in the pantheon of battery technologies, there still remain challenges to overcome - perhaps the most significant of which is the ongoing development of optimal cathode materials.Sodium Mn-rich layered oxides, i.e. NaxMn1-yMyO2 (y ≤ 0.33; M is one or more transition metals, such as Ni, Ti, Fe, etc.), have proven to be a promising family of SIB cathode materials with a low cost, highly tuneable, and environmentally friendly nature synergises well with the main advantages of SIBs.[1] Considerable research in this area, using a variety of conventional and specialised techniques, has led to an increased understanding of the nature and behaviour of these materials, and the key factors affecting their electrochemistry.[1-4]Performance of these materials is frequently governed by their structure, and in this work, we will highlight the importance of taking this into consideration. For example, while Manganese-rich layered oxides are particularly attractive due to their combination of low cost and low toxicity, their performances are often hindered by the effect of Jahn-Teller distortion (resulting from the presence of Mn3+).[5] We will not only discuss this in detail, but also highlight mitigation strategies – such as doping with electrochemically active (e.g. Fe) and inactive (e.g. Mg, Ti) elements, or synergetic P2/O3 combination effect.[5–8] This understanding has enabled the rapid investigation of not only suitable elements (selected with careful attention to electrochemical performance, cost, scarcity, etc.) but also appropriate degrees of doping and substitution.In this presentation, we will highlight some of the most significant Mn-rich materials and their properties, as well as examining and explaining the key parameters and factors which determine their performance. We will explain how this understanding has been used to develop a rational design approach, before summarising the trends in this area and areas of future exploitation.

Unraveling Na and F coupling effects in stabilizing Li, Mn-rich layered oxide cathodes via local ordering modification

Regardless of the prevailing capacity and energy density of lithium, manganese-rich layered oxide (LMR-NMC) cathodes, continuous decay of voltage and overall energy density during cycling hinders this material from commercialization in Li-ion batteries. Although significant work focuses on single doping of Na and F, analysis in portraying the benefit of these ions in diminishing the structural distortion during activation cycle is in doubt. Herein, the effects of co-doping Na and F into the LMR-NMC structure in stabilizing the structure and mitigating oxygen loss during the first cycle are closely examined via in situ x-ray measurements. Na and F co-doping shows a 30% lower degree of Li+/Ni2+ mixing in the Li layer (C2/m structure), 50% reduced Debye-Waller factor of Mn-O bonding, increase reversible TM migration, and faster Li diffusion relative to the pristine material. Due to the utilization of Ni redox chemistry below 4.4 V, less oxygen redox is required for charge compensation at high voltage. This study offers the first instance to quantitatively evaluate the effects of co-doping Na and F in LMR-NMC cathode in order to minimize voltage degradation by altering the local ordering of O3-type structure, which may rationalize strategies to overcome the issues of the material.

Strain engineering by atomic lattice locking in P2-type layered oxide cathode for high-voltage sodium-ion batteries

Abstract Developing high-voltage cathode materials is the key to overcome the obstacles of low energy density for sodium-ion batteries (SIBs). P2-type manganese-rich layered oxides are considered as an appealing cathode material for SIBs, but still suffer from severe capacity and voltage decay. As the underlying cause, inhomogeneous interlaminar stress originated from the intrinsic structural transition brings out the generation and propagation of surface cracks, and should be tackled. Herein, we construct an interlocking spinel-like/layered heterostructure via boric acid treatment approach. The well-designed epitaxial spinel-like nanolayer effectively inhibits the unfavorable P2-OP4 phase transition associated with dramatic volume change over 4.1 V, preventing the accumulation of inhomogeneous stress as well as the lattice distortion. The generation and propagation of intragranular cracks are fundamentally prohibited, resulting in improved structural durability and capacity stability. This present work sheds light on the importance of interface engineering of high-voltage cathode materials for SIBs.

Sequential delithiation behavior and structural rearrangement of a nanoscale composite-structured Li1.2Ni0.2Mn0.6O2 during charge\u2013discharge cycles

Lithium- and manganese-rich layered oxides (LMRs) are promising positive electrode materials for next-generation rechargeable lithium-ion batteries. Herein, the structural evolution of Li1.2Ni0.2Mn0.6O2 during the initial charge–discharge cycle was examined using synchrotron-radiation X-ray diffraction, X-ray absorption spectroscopy, and nuclear magnetic resonance spectroscopy to elucidate the unique delithiation behavior. The pristine material contained a composite layered structure composed of Ni-free and Ni-doped Li2MnO3 and LiMO2 (M = Ni, Mn) nanoscale domains, and Li ions were sequentially and inhomogeneously extracted from the composite structure. Delithiation from the LiMO2 domain was observed in the potential slope region associated with the Ni2+/Ni4+ redox couple. Li ions were then extracted from the Li2MnO3 domain during the potential plateau and remained mostly in the Ni-doped Li2MnO3 domain at 4.8 V. In addition, structural transformation into a spinel-like phase was partly observed, which is associated with oxygen loss and cation migration within the Li2MnO3 domain. During Li intercalation, cation remigration and mixing resulted in a domainless layered structure with a chemical composition similar to that of LiNi0.25Mn0.75O2. After the structural activation, the Li ions were reversibly extracted from the newly formed domainless structure.

Large-scale synthesis of lithium- and manganese-rich materials with uniform thin-film Al2O3 coating for stable cathode cycling

The lithium- and manganese-rich layered oxide (LMR) holds great promise as a cathode material for lithium-ion battery (LIB) applications due to its high capacity, high voltage and low cost. Unfortunately, its poor initial Coulombic efficiency (ICE) and unstable electrode/electrolyte interface with continuous growth of the solid electrolyte interphase leads to high impedance and large overpotential. These effects cause severe capacity loss and safety issues. In this work, we have developed a novel approach to fabricate a stable LMR cathode with a uniform thin layer of aluminum oxide (Al2O3) coated on the surface of the LMR particles. This synthesis approach uses the microemulsion method that is environment-friendly, cost-effective and can be easily scaled. Typically, an 8-nm layer of Al2O3 is shown to be effective in stabilizing the electrode/electrolyte interface (enhanced ICE to 82.0% and moderate impedance increase over 200 cycles). Moreover, the phase transformation from layered to spinel is inhibited (96.3% average voltage retention) and thermal stability of the structure is significantly increased (heat release reduced by 72.4%). This study opens up a new avenue to address interface issues in LIB cathodes and prompts the practical applications of high capacity and voltage materials for high energy density batteries.

Systematic Study of Different Anion Doping on the Electrochemical Performance of Cobalt-Free Lithium–Manganese-Rich Layered Cathode

Regardless of the appealingly high energy density (1000 Wh kg–1) of the lithium–manganese-rich layered oxide cathode (LMR-NMO), this material still suffers from rapid capacity and voltage decay aft...