Layered Transition Metal Research Articles

Regulating the Intralayer Cation Disorder in Layered Lithium-Rich Cathodes to Improve Cycle Performance.

The Li/Mn ordered structure of lithium-rich (LR) cathodes leads to the heterogeneous Li2MnO3 and LiTMO2 components, readily triggering structural degeneration and performance degradation in long-term cycling. However, the lack of guiding principles for promoting cation disorder within the transition metal (TM) layers has posed a persistent challenge in designing homogeneous layered LR cathodes. Herein, the (Li + Mn)TM content in the TM layer as a criterion for the design of cation-disordered layered LR cathodes is proposed. The intralayer cation disorder can be achieved by tuning the (Li + Mn)TM content less than 0.5 combined with incorporating the solute ions with suitable ionic radii. For a multicomponent LR nickel cobalt manganese (LRNCM) oxides system, multiscale structural analyses reveal that cation-disordered layered Li1.1(Ni0.6Co0.1Mn0.3)0.9O2 (LR613) exhibits enhanced compositional homogeneity and higher R m symmetry. The developed LR613 cathode undergoes a solid-solution reaction during Li+ deintercalation and mitigates voltage decay during cycling. It is elucidated that intralayer cation disorder effectively alleviates microstrain within the cathode structure and enhances overall structural stability. This comprehensive understanding of the composition-structure-electrochemical behavior relationship inspires the development of durable cation-disordered layered LR cathodes through composition tuning.

Depth‐of‐Discharge Dependent Capacity Decay Induced by the Accumulation of Oxidized Lattice Oxygen in Li‐Rich Layered Oxide Cathode

AbstractMore and more basic practical application scenarios have been gradually ignored/disregarded, in fundamental research on rechargeable batteries, e.g. assessing cycle life under various depths‐of‐discharge (DODs). Herein, although benefit from the additional energy density introduced by anionic redox, we critically revealed that lithium‐rich layered oxide (LRLO) cathodes present anomalously poor capacity retention at low‐DOD cycling, which is essentially different from typical layered cathodes (e.g. NCM), and pose a formidable impediment to the practical application of LRLO. We systemically demonstrated that DOD‐dependent capacity decay is induced by the anionic redox and accumulation of oxidized lattice oxygen (On−). Upon low‐DOD cycling, the accumulation of On− and the persistent presence of vacancies in the transition metal (TM) layer intensified the in‐plane migration of TM, exacerbating the expansion of vacancy clusters, which further facilitated detrimental out‐of‐plane TM migration. As a result, the aggravated structural degradation of LRLO at low‐DOD impeded reversible Li+ intercalation, resulting in rapid capacity decay. Furthermore, prolonged accumulation of On− persistently corroded the electrode‐electrolyte interface, especially negative for pouch‐type full‐cells with the shuttle effect. Once the “double‐edged sword” effect of anionic redox being elucidated under practical condition, corresponding modification strategies/routes would become distinct for accelerating the practical application of LRLO.

Depth-of-Discharge Dependent Capacity Decay Induced by the Accumulation of Oxidized Lattice Oxygen in Li-Rich Layered Oxide Cathode.

More and more basic practical application scenarios have been gradually ignored/disregarded, in fundamental research on rechargeable batteries, e.g. assessing cycle life under various depths-of-discharge (DODs). Herein, although benefit from the additional energy density introduced by anionic redox, we critically revealed that lithium-rich layered oxide (LRLO) cathodes present anomalously poor capacity retention at low-DOD cycling, which is essentially different from typical layered cathodes (e.g. NCM), and pose a formidable impediment to the practical application of LRLO. We systemically demonstrated that DOD-dependent capacity decay is induced by the anionic redox and accumulation of oxidized lattice oxygen (On-). Upon low-DOD cycling, the accumulation of On- and the persistent presence of vacancies in the transition metal (TM) layer intensified the in-plane migration of TM, exacerbating the expansion of vacancy clusters, which further facilitated detrimental out-of-plane TM migration. As a result, the aggravated structural degradation of LRLO at low-DOD impeded reversible Li+ intercalation, resulting in rapid capacity decay. Furthermore, prolonged accumulation of On- persistently corroded the electrode-electrolyte interface, especially negative for pouch-type full-cells with the shuttle effect. Once the "double-edged sword" effect of anionic redox being elucidated under practical condition, corresponding modification strategies/routes would become distinct for accelerating the practical application of LRLO.

Quantitative Identification of Dopant Occupation in Li-Rich Cathodes.

Elemental doping is widely used to improve the performance of cathode materials in lithium-ion batteries. However, macroscopic/statistical investigation on how doping sites are distributed in the material lattice, despite being a key prerequisite for understanding and manipulating the doping effect, has not been effectively established. Herein, to solve this predicament, a universal strategy is proposed to quantitatively identify the locations of Al and Mg dopants in lithium-rich layered oxides (LLOs). Solid evidence confirms that Al prefers to occupy the transition metal (TM) layer, while Mg evenly occupies both TM and Li layers. As a result, Mg significantly reduces the thickness of LiO2 slabs at room temperature, which will increase the energy barrier of oxygen activation and enhance the structure stability of LLOs. The suppressed oxygen activity in Mg-doped LLO can be kinetically unlocked at 55°C. The different characteristics of Al and Mg enlighten an Al/Mg co-doping strategy to optimize LLOs, which significantly improves the cycle performance while lifting the capacity. These insights from the quantitative identification of doping sites shed light on the manipulation of doping effects toward better cathodes.

Layered Transition Metal Carbides/Nitrides: From Chemical Etching to Chemical Editing

Layered Transition Metal Carbides/Nitrides: From Chemical Etching to Chemical Editing

Tailoring superstructure units for improved oxygen redox activity in Li-rich layered oxide battery’s positive electrodes

The high-voltage oxygen redox activity of Li-rich layered oxides enables additional capacity beyond conventional transition metal (TM) redox contributions and drives the development of positive electrode active materials in secondary Li-based batteries. However, Li-rich layered oxides often face voltage decay during battery operation. In particular, although Li-rich positive electrode active materials with a high nickel content demonstrate improved voltage stability, they suffer from poor discharge capacity. Here, via physicochemical and electrochemical measurements, we investigate the correlation between oxygen redox activity and superstructure units in Li-rich layered oxides, specifically the fractions of LiMn6 and Ni4+-stabilized LiNiMn5 within the TM layer. We prove that an excess of LiNiMn5 hinders the extraction/insertion of lithium ions during Li metal coin cell charging/discharging, resulting in incomplete oxygen redox activity at a cell potential of about 3.3 V. We also demonstrate that lithium content adjustment could be a beneficial approach to tailor the superstructure units. Indeed, we report an improved oxygen redox reversibility for an optimized Li-rich layered oxide with fewer LiNiMn5 units.

Modulating Local Oxygen Coordination to Achieve Highly Reversible Anionic Redox and Negligible Voltage Decay in O2‐Type Layered Cathodes for Li‐Ion Batteries

AbstractO2‐type layered oxides have emerged as promising cathode materials for high‐energy lithium‐ion batteries, offering a solution to mitigate voltage decay through reversible transition metal (TM) migration between TM and Li layers during cycling. However, achieving a fully reversible oxygen redox remains a significant challenge. Here, this is addressed by introducing Li─O─Li configurations in the layered structure of Li0.85□0.15[Li0.08□0.04Ni0.22Mn0.66]O2 (O2‐LLNMO), where □ represents vacancies. This adjustment alters the redox‐active oxygen environment and increases the energy gap between the O 2p nonbonding and TM─O antibonding bands. As a result, the contribution of lattice oxygen to capacity is significantly enhanced, improving the reversibility of oxygen redox processes. The O2‐LLNMO cathode demonstrates minimal voltage decay (0.13 mV per cycle) and excellent cycling stability, retaining 95.8% of its capacity after 100 cycles. A novel strategy is presented to design high‐performance layered oxides with stable anionic redox activity, advancing the development of next‐generation lithium‐ion batteries.

Ultrafast lattice engineering for high energy density and high-rate sodium-ion layered oxide cathodes

Sodium-ion batteries attract significant interest for large-scale energy storage owing to abundant sodium reserves, while challenges remain in the high synthesis energy consumption, long synthesis period, and poor electrochemical performance of sodium-ion layered oxide materials. This study presents a general high-temperature thermal shock (HTS) strategy to synthesize and optimize sodium-ion layered oxides. The rapid ramping, sintering, and cooling processes minimize volatile sodium loss during HTS, facilitating the improvement of phase purity and effectively optimizing the microstructure of materials in a non-equilibrium state. As a proof of concept, Mn-based Na0.67MnO2 treated with HTS (NMOHTS) suppresses Mn ion vacancy within transition material layers, thereby increasing the redox centers and lowering the Mn 3d orbital energy level. Besides, the formation of transition metal layer stacking faults mitigates the structural transformation and Na+-vacancies ordering arrangement during cycling. Consequently, the energy density of the NMOHTS increases by 21.5 % to 559 Wh kg-1, with an outstanding rate capability of 108 mAh g-1 at 10C and an impressive capacity retention of 93.7 % after 300 cycles at 1C. In addition, we demonstrate the universality of HTS in synthesizing various other sodium-ion layered oxides, including nickel-based and iron-based cathodes, as well as in activating degraded materials.

Enhancement of transverse magneto-optical Kerr effect using transition metals in a grating-based gyro-electric structure

Abstract This study proposes a new structure based on a grating with magneto-optical properties and a layer of transition metals (platinum, silver, copper, gold, and palladium). The research aims to investigate the impact of surface plasmon polaritons on enhancing the transverse magneto-optical Kerr effect when exposed to TM- and TE-polarized waves. After optimizing the structure’s dimensions, it was determined that the transition metal layer should have a thickness of 20 nm. The study involves applying TM- and TE-polarized light to the structure to observe variations in reflected light and the transverse magneto-optical Kerr effect. The findings reveal that the gyro-electric magneto-optics material responds to TMpolarized waves, and silver and gold are identified as the most effective metals for the proposed structure.

Introducing strong metal–oxygen bonds to suppress the Jahn-Teller effect and enhance the structural stability of Ni/Co-free Mn-based layered oxide cathodes for potassium-ion batteries

Mn-based layered oxides (KMO) have emerged as one of the promising low-cost cathodes for potassium-ion batteries (PIBs). However, due to the multiple-phase transitions and the distortion in the MnO6 structure induced by the Jahn-Teller (JT) effect associated with Mn-ion, the cathode exhibits poor structural stability. Herein, we propose a strategy to enhance structural stability by introducing robust metal–oxygen (M–O) bonds, which can realize the pinning effect to constrain the distortion in the transition metal (TM) layer. Concurrently, all the elements employed have exceptionally high crustal abundance. As a proof of concept, the designed K0.5Mn0.9Mg0.025Ti0.025Al0.05O2 cathode exhibited a discharge capacity of approximately 100 mA h g−1 at 20 mA g−1 with 79% capacity retention over 50 cycles, and 73% capacity retention over 200 cycles at 200 mA g−1, showcased much better battery performance than the designed cathode with less robust M–O bonds. The properties of the formed M–O bonds were investigated using theoretical calculations. The enhanced dynamics, mitigated JT effect, and improved structural stability were elucidated through the in-situ X-ray diffractometer (XRD), in-situ electrochemical impedance spectroscopy (EIS) (and distribution of relaxation times (DRT) method), and ex-situ X-ray absorption fine structure (XAFS) tests. This study holds substantial reference value for the future design of cost-effective Mn-based layered cathodes for PIBs.

High-Entropy Layered Oxide Cathode Materials with Moderated Interlayer Spacing and Enhanced Kinetics for Sodium-Ion Batteries.

Sodium-ion batteries (SIBs) with low cost and environmentally friendly features have recently attracted significant attention for renewable energy storage. Sodium layer oxides stand out as a type of promising cathode material for SIBs owing to their high capacity, good rate performance, and high compatibility for manufacturing. However, the poor cycling stability of layer oxide cathodes due to structure distortion greatly impacts their practical applications. Herein, a high entropy doped Cu, Fe, and Mn-based layered oxide (HE-CFMO), Na0.95Li0.05Mg0.05Cu0.20Fe0.22Mn0.35Ti0.13O2 for high-performance SIBs, is designed. The HE-CFMO cathode possesses high-entropy transition metal (TM) layers with a homogeneous stress distribution, providing a moderated interlayer spacing to maintain the structure stability and enhance Na+ ion diffusion. In addition, Li doping in TM layers increases the Mn valence state, which effectively suppresses John-Teller effect, thus stabilizing the layered structure during cycling. Furthermore, the use of nontoxic and low-cost raw materials benefits future commercialization and reduces the risk of environmental pollution. As a result, the HE-CFMO cathode exhibits a super cycling performance with a 95% capacity retention after 300 cycles. This work provides a promising strategy to improve the structure stability and reaction kinetics of cathode materials for SIBs.

Effect of the position of Mg replacing Ni on O3-NaNi1/3Fe1/3Mn1/3O2 on the structural stability of cathode materials

O3-NaNi1/3Fe1/3Mn1/3O2 (NaNFM) materials are susceptible to complex phase transitions during electrical cycling leading to poor structural, capacity retention and multiplicity properties. These drawbacks hinder the application of NaNFM in sodium-ion batteries. Here, Mg2+ with larger ionic radius was used to dope its transition metal layer Ni site. The effects of Mg2+ doped NaNFM crystal structure and transition metal valence states on its electrochemical properties were investigated by XRD, SEM, and XPS. The capacity retention of NaNMFM-0.02 (84.05 %) was higher than that of NaNFM (73 %) after 200 cycles of the material at 5C. In addition, NaNMFM-0.02 achieved a first discharge specific capacity of 146.5 mAh/g at high voltage. Based on structural and electrochemical analyses, this improvement is attributed to the fact that magnesium acts as a “pillar” to stabilize the crystal structure of NaNFM, while magnesium doping reduces the Jahn-Teller effect. As a result, the material has better electrochemical properties.

Roles of fast-ion conductor NaAlO2 modifying P2-Na0.67Ni0.3Mn0.6Co0.1O2 cathode material for sodium-ion batteries

P2-type layered oxides are promising candidates for sodium-ion batteries. However, structural instability and sluggish Na⁺ diffusion kinetics hinder their further commercialization. In this study, NaAlO2, which possesses a similar α-NaFeO2 layer structure, is coated onto the surface of P2-Na0.67Ni0.3Mn0.6Co0.1O2 (NNMC) to enhance its electrochemical performance as a novel cathode for sodium-ion batteries. A variety of experimental results and characterizations reveal that the thin NaAlO2 coating layer significantly reduces side reactions and facilitates the diffusion of Na⁺ at the interface between the cathode and the electrolyte. Moreover, the introduction of partial Al ions into the transition-metal layers enlarge the interlayer spacing, and decrease the content of Mn3+. As a result, the NNMC cathode material, modified with 3 wt% NaAlO2, demonstrated remarkable electrochemical performance. The initial specific discharge capacity was recorded at 137.7 mA h g−1 at 0.2 C, and an impressive discharge capacity of 38.2 mA h g−1 was attained at 20 C. Following 100 cycles at a rate of 0.5 C, the capacity retention rate was determined to be 99.6 %.

Stable electrochemical properties of trace titanium doping layered P3-type K0.5Mn0.92Ti0.08O2 cathode material for potassium ion batteries

The wide application of potassium ion batteries (PIBs) urgently requires the development of ideal cathode materials with low cost, good reaction kinetics and structural stability. Here, a titanium-doped K0.5Mn0.92Ti0.08O2 cathode material for potassium ion batteries is developed by doping modification strategy using a high-temperature solid-state method. The structure and performance structure-activity relationship of binary K0.5Mn1-xTixO2 cathode materials doped with non-electrochemically active element Ti4+ are studied experimentally and theoretically. With the introduction of Ti4+, when the doping amount is <10 mol%, the doped solid solution is hexagonal P3 phase, and the transition metal layer spacing increases. The non-equivalent doping affects the relative content of Mn3+/Mn4+, smoothes the redox peak in the electrochemical process, reduces the doping formation energy, and improves the structural stability. The ex-situ XRD fine structure study of the electrochemical process shows that the structural change of the material during the discharge process is suppressed after doping. The best Ti-doped cathode material K0.5Mn0.92Ti0.08O2 has an initial discharge capacity of 126.9 mAh·g−1 at a current density of 20 mA·g−1, and the capacity retention rate is 53.7 % after 100 cycles. This work provides a feasible strategy for the construction of stable electrode materials for PIBs.

Exploring Electrolyte Adsorption on the Different Types of Layered Cathode Surfaces in Lithium-Ion Batteries via a Universal Neural Network Potential Method.

LiNi x Mn y Co z O2 (NCM) is a promising cathode material for lithium-ion batteries. Their long-term stability and impedance growth as cycles are strongly influenced by the properties of the cathode electrolyte interface (CEI), formed by the reaction between the electrolyte and electrode surface. Understanding of these interactions at the atomic level of the NCM electrode surface and electrolyte will provide a new strategic approach for the design of a highly functional CEI layer. In this study, we explored the influence of Ni content in transition metal layers on surface energies under different synthetic conditions and terminations using a density functional theory (DFT) validated universal neural network potential (UNNP) method. Furthermore, we investigated the adsorption of ethylene carbonate (EC) and dimethyl carbonate (DMC) on the most favorable NCM surfaces. EC and DMC displayed similar adsorption energy trends; however, differences were observed in the preferred configurations, which can affect the formation of the CEI.

Slope-structure design towards high-stability P2-Na0.67MnO2 cathode

Layered Mn-based oxide P2-Na0.67MnO2 (NMO) arouses enormous interest for its high specific capacity, easy preparation and low cost. Meanwhile, the P2 → O2 phase transition derived from the slippage of transition metal (TM) layer leads to the inferior performance. Herein, we design a co-doping into Na+ (102 pm) lattice site with smaller-sized Li+ (76 pm) and larger-sized K+ (138 pm) to construct a slope-structured P2-Na0.63K0.02Li0.02MnO2 (NKLMO). The anchored Li+ and K+ can serve as pillar effects and form a geometrically stable resembling triangular structure in the Na-interlayer. Moreover, such a slope-structure is clearly verified by the HRTEM images. In-situ XRD and in-situ EIS tests efficaciously clarify the improved structural stability and even lower impedance during cycling within 2.0–4.2 V, respectively. DFT calculations further confirm the stronger metallicity of NKLMO electrode than the bare NMO originated from the more mobile free electrons surrounding the vicinity of Fermi level. By grace of the more stable slope-structure and faster reaction kinetics, NKLMO is capable of displaying high initial capacity (206.5 mA h/g) and energy density (540 W h kg−1), with a competitive cycling stability at both low and high current rates (96 %@100 cycles@0.1C; 88.4 %@500 cycles@5C). This slope-design is above rubies for tuning chemistry environment to exploit high-stability P2-phase cathodes for sodium-ion batteries.

Insightful interpretation of the unique stacking faults of Na3Ni2SbO6 through cobalt doping for enhanced sodium-ion battery performance

The O3-Na3Ni2SbO6 compound, with its hexagonal honeycomb cationic ordering, is a promising sodium-ion battery (SIB) cathode due to its phase transition steps and high average voltage. In this study, various concentrations of cobalt (Co) are doped into Na3Ni2SbO6 to replace nickel (Ni), increasing disorder within the transition metal layers. Co doping introduced specific stacking faults along the c-axis direction, resulting in an ambiguous configuration of Sb/Ni(Co) within each transition metal layer, while maintaining the honeycomb order. This disorderly arrangement optimized the electronic structure and reduced the energy barrier for reactions. Na3Ni1.6Co0.4SbO6 exhibited superior performance, with a higher initial discharge capacity (137.8 mAh g-1 at 0.1 C) and better rate performance (87 mAh g-1 at 5 C) compared to Na3Ni2SbO6 (113.6 mAh g-1 at 0.1 C, 74 mAh g-1 at 5 C), including improved long-term cyclic stability. The findings demonstrate that electrochemical performance can be significantly enhanced through atomic layer stacking disorder and the Na coordination environment, which is influenced by Na ion extraction and insertion, resulting in more gradual and smaller variations in lattice parameters, electronic structure, and crystal defects. This study provides a foundation for future designs of sodium-ion battery cathode materials with improved performance.

Revealing Gliding-Induced Structural Distortion in High-Nickel Layered Oxide Cathodes for Lithium-Ion Batteries.

After charging to a high state-of-charge (SoC), layered oxide cathodes exhibit high capacities but suffer from gliding-induced structural distortions caused by deep Li depletion within alkali metal (AM) layers, especially for high-nickel candidates. In this study, we identify the essential structure of the detrimental H3 phase formed at high SoC to be an intergrowth structure characterized by random sequences of the O3 and O1 slabs, where the O3 slabs represent Li-rich layers and the O1 slabs denote Li-depleted (or empty) layers that glide from the O3 slabs. Moreover, we adopt two doping strategies targeting different doping sites to eliminate the formation of Li-vacant O1 slabs. First, we introduce direct transition metal (TM) pillars between TMO2 slabs achieved through dopants (e.g., Nb) positioned within AM layers, significantly improving the cycling stability. Second, we introduce indirect Li pillars achieved through dopants located at TM layers to adjust the Li-O bond strength. While this strategy can regulate the uniformity of Li at the slab level, it results in an uneven Li distribution at the particle scale, ultimately failing to enhance the electrochemical performance. Our established research strategy facilitates the realization of diverse pillars between TMO2 slabs through doping, thereby offering guidance for stabilizing high-capacity layered oxide cathodes at high SoC.

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.

Enhanced adsorption of radioactive cesium from nuclear wastewater using ZIF-67 laminated 2D MXene Ti3C2

Development of nuclear industry has caused severe water pollution. Adsorptive removal of radionuclides from wastewater has been regarded as effective solution for environment. However, developing adsorbents with high adsorption capacity and selectivity for removal of radionuclides (such as 137Cs) is still a challenge. Herein, we adopted an in situ assemble strategy to construct a novel composite, in which zeolitic imidazolate framework (ZIF-67) was grafted into two-dimension (2D) layers of transition metal carbides/nitrides (MXenes) Ti3C2, and used it in adsorptive removal of Cs+ from wastewater. Laminated and pillaring effect of ZIF-67 increased interlayer spacing and specific surface area of Ti3C2, significantly enhancing Cs+ adsorption. MXenes matrix provided the main adsorptive sites and interaction to stabilize Cs+, while the hybrid ZIF-67 assisted adsorption. The adsorbent achieved 96.2 % removal for 5 mg·L-1 of Cs+ within 6 h, and 50.0 mg·g−1 of maximum adsorption capacity, with good recyclability for 4 times. Ion competition, kinetics and thermodynamics were studied in detail to obtain the behavior of Cs+ adsorption. Finally, adsorption mechanism was proposed that [Ti − O] − H+ and [Ti − O] groups of 2D Ti3C2 were main adsorptive sites to participate in ion exchange and complexation with Cs+, respectively, while 2-methylimidazole (2-MI) ligands in ZIF-67 were synergetic adsorption sites.