Mn-based Oxides Research Articles

From Liquid to Solid-State Batteries: Li-Rich Mn-Based Layered Oxides as Emerging Cathodes with High Energy Density.

Li-rich Mn-based (LRMO) cathode materials have attracted widespread attention due to their high specific capacity, energy density, and cost-effectiveness. However, challenges such as poor cycling stability, voltage deca,y and oxygen escape limit their commercial application in liquid Li-ion batteries. Consequently, there is a growing interest in the development of safe and resilient all-solid-state batteries (ASSBs), driven by their remarkable safety features and superior energy density. ASSBs based on LRMO cathodes offer distinct advantages over conventional liquid Li-ion batteries, including long-term cycle stability, thermal and wider electrochemical windows stability, as well as the prevention of transition metal dissolution. This review aims to recapitulate the challenges and fundamental understanding associated with the application of LRMO cathodes in ASSBs. Additionally, it proposes the mechanisms of interfacial mechanical and chemical instability, introduces noteworthy strategies to enhance oxygen redox reversibility, enhances high-voltage interfacial stability, and optimizes Li+ transfer kinetics. Furthermore, it suggests potential research approaches to facilitate the large-scale implementation of LRMO cathodes in ASSBs.

Mechanistic Insight into the Promotion of the Low-Temperature NH3-SCR Activity over NiMnFeOx LDO Catalysts: A Combined Experimental and DFT Study.

Mn-based catalysts have attracted much attention in the field of the low-temperature NH3 selective catalytic reduction (NH3-SCR) of NO. However, their poor SO2 resistance, low N2 selectivity, and narrow operation window limit the industrial application of Mn-based oxide catalysts. In this work, NiMnFeOx catalysts were prepared by the layered double hydroxide (LDH)-derived oxide method, and the optimized Ni0.5Mn0.5Fe0.5Ox catalyst had the best denitration activity, excellent N2 selectivity, a wider active temperature range (100-250 °C), higher thermal stability, and better H2O and/or SO2 resistance. A transient reaction revealed that Ni0.5Mn0.5Fe0.5Ox inhibited the NH3 + O2 + NOx pathway to generate N2O, which may be the main reason for its improved N2 selectivity. Combining experimental measurements and density functional theory (DFT) calculations, we elucidated at the atomic level that sulfated NiMnFeOx (111) induces the adjustment of the acidity/basicity of up and down spins and the ligand field reconfiguration of the Mn sites, which improves the overall reactivity of NiMnFeOx catalysts. This work provides atomic-level insights into the promotion of NH3-SCR activity by NiMnFeOx composite oxides, which are important for the practical design of future low-temperature SCR technologies.

Achieving the High Capacity and High Stability of Li-Rich Oxide Cathode in Garnet-Based Solid-State Battery.

Solid-state batteries (SSBs) based on Li-rich Mn-based oxide (LRMO) cathodes attract much attention because of their high energy density as well as high safety. But their development was seriously hindered by the interfacial instability and inferior electrochemical performance. Herein, we design a three-dimensional foam-structured GaN-Li composite anode and successfully construct a high-performance SSB based on Co-free Li1.2 Ni0.2 Mn0.6 O2 cathode and Li6.5 La3 Zr1.5 Ta0.5 O12 (LLZTO) solid electrolyte. The interfacial resistance is considerably reduced to only 1.53 Ω cm2 and the assembled Li symmetric cell is stably cycled more than 10,000 h at 0.1-0.2 mA cm-2 . The full battery shows a high initial capacity of 245 mAh g-1 at 0.1 C and does not show any capacity degradation after 200 cycles at 0.2 C (≈100 %). The voltage decay is well suppressed and it is significantly decreased from 2.96 mV/cycle to only 0.66 mV/cycle. The SSB also shows a very high rate capability (≈170 mAh g-1 at 1 C) comparable to a liquid electrolyte-based battery. Moreover, the oxygen anion redox (OAR) reversibility of LRMO in SSB is much higher than that in liquid electrolyte-based cells. This study offers a distinct strategy for constructing high-performance LRMO-based SSBs and sheds light on the development and application of high-energy density SSBs.

Multifunctional surface structure with enhanced electron and ion conductivities for superior electrochemical performance of Co-free Li-rich Mn-based layered oxide cathodes

Co-free Li-rich Mn-based layered oxides (LRMLOs) are attractive cathode materials for lithium-ion batteries due to their low cost, high energy density and environmental friendliness. However, they also suffer from the drawbacks of low initial Coulombic efficiency, rapid voltage fading and capacity decay, and poor rate performance as the general LRMLO cathode, which prevent their practical applications. In the present work, a multilayer surface coating composed of Li2B4O7/B2O3 and a spinel heterostructure rich-in oxygen vacancies are in-situ formed at the surface of the Co-free LRMLO particles by a facile thermal reduction treatment with NH4B5O8. The multilayer surface improves greatly the electron and ion conductivities, and plays significantly synergistic roles on suppressing oxygen release, reducing the dissolution of Mn and Ni elements, retarding the structure transformation from layered to spinel, and preventing the side reaction of the active material with electrolyte during cycling for the cathodes. As a result, the overall electrochemical properties of the cathodes are significantly improved. With an optimized addition of 10 wt% NH4B5O8, the initial Coulombic efficiency of the cathode is as high as 90.0%, and a capacity of 275 mAh g-1 is obtained at 0.1 C (1 C = 200 mA g-1) with the capacity retention of 98.5% after 100 cycles. A capacity of 194 mAh g-1 is maintained after 300 cycles at 1 C, with the capacity retention of 92.8%. A capacity of 117 mAh g-1 is obtained at a high rate of 20 C. In addition, the voltage fading during cycling is also greatly inhibited. The structure evolution of the cathode material during cycling is systematically investigated and the mechanism for the improved electrochemical properties is proposed. The present work provides a new surface structure design strategy and the method for enhancing the overall electrochemical performance of Co-free Li-rich Mn-based layered oxide cathodes.

Unlocking the Potential of Li-Rich Mn-Based Oxides for High-Rate Rechargeable Lithium-Ion Batteries.

Lithium-rich Mn-based oxides have gained significant attention worldwide as potential cathode materials for the next generation of high-energy density lithium-ion batteries. Nonetheless, the inferior rate capability and voltage decay issues present formidable challenges. Here, a Li-rich material equipped with quasi-three-dimensional (quasi-3D)Li-ion diffusion channels is initially synthesized by introducing twin structures with high Li-ion diffusion coefficients into the crystal and constructing a "bridge" between different Li-ion diffusion tunnels. The as-prepared material exhibits monodispersed micron-sized primary particles (MP), delivering a specific capacity of 303mAhg-1 at 0.1 C and an impressive capacity of 253mAhg-1 at 1 C. More importantly, the twin structure also serves as a "breakwater" to inhibit the migration of Mn ions and improve the overall structural stability, leading to cycling stability with 85% capacity retention at 1 Cafter 200 cycles. The proposed strategy of constructing quasi-3Dchannels in the layered Li-rich cathodes will open up new avenues for the research and development of other layered oxide cathodes, with potential applications in industry.

Component design and regulation to stabilize P3-type Mn-based layered cathodes for potassium-ion batteries

Mn-based layered oxides with high theoretical capacity are one of the most promising cathode materials for potassium-ion batteries. However, the Jahn-teller distortion of Mn3+ in Mn-based layered cathodes always brings about harmful disordered structure and irreversible phase transition, resulting in severe degradation of electrochemical performance. Herein, we synthesized P3–K0.5Mn0.6Ni0.2M0.2O2 (M = Fe, Co, FeCo) and systematically investigate the effect of component regulation on the layered structure and electrochemical properties. The P3–K0.5Mn0.6Ni0.2Co0.2O2 exhibits a discharge capacity of 73.77 mAh g−1, demonstrating an excellent capacity retention rate of 70.17 % after 120 cycles at 50 mA g−1. In-depth analysis reveals that P3–K0.5Mn0.6Ni0.2Co0.2O2 possesses a larger K+ layer spacing, making the insertion/extraction of potassium ions become much easier. Furthermore, the introduction of Co into the transition metal layer enhances the content of Mn4+, thereby inhibiting Jahn-Teller distortion and improving structural stability. Especially, the P3–K0.5Mn0.6Ni0.2Co0.2O2 shows a highly reversible single-phase solid solution reaction during the initial cycle, which means the detrimental phase transition of P3–O3 caused by Jahn-Teller effect is effectively suppressed. This work contributes to a better understanding of the effect of component design and regulation on the performance of the layered oxides cathode and provide insight into the design of high-performance cathode materials for potassium-ion batteries.

Surface Modification Driven Initial Coulombic Efficiency and Rate Performance Enhancement of Li1.2 Mn0.54 Ni0.13 Co0.13 O2 Cathode.

Due to its high energy density and low cost, Li-rich Mn-based layered oxides are considered potential cathode materials for next generation Li-ion batteries. However, they still suffer from the serious obstacle of low initial Coulombic efficiency, which is detrimental to their practical application. Here, an efficient surface modification method via NH4 H2 PO4 assisted pyrolysis is performed to improve the Coulombic efficiency of Li1.2 Mn0.54 Ni0.13 Co0.13 O2 , where appropriate oxygen vacancies, Li3 PO4 and spinel phase are synchronously generated in the surface layer of LMR microspheres. Under the synergistic effect of the oxygen vacancies and spinel phase, the unavoidable oxygen release in the cycling process was effectively suppressed. Moreover, the induced Li3 PO4 nanolayer could boost the lithium-ion diffusion and mitigate the dissolution of transition metal ions, especially manganese ions, in the material. The optimally modified sample yielded an impressive initial Coulombic efficiency and outstanding rate performance.

SnO2 coating to stabilize Mn-based layered oxide cathode materials for sodium-ion batteries

Thanks to high theoretical capacity and good ionic conductivity, Mn-based layered metal oxides are considered to be promising cathode materials for sodium-ion batteries (SIBs). However, the irreversible structural change and oxygen loss during sodiation/desodiation processes lead to rapid capacity attenuation. Herein, SnO2 surface coating was adopted for the first time to improve the Na-storage performance of Na0.6[Li0.2Mn0.8]O2 (NLMO) through solid-phase heat treatment with a subsequent liquid-phase method. The optimized 1 wt% SnO2 coated NLMO demonstrated a capacity of 103 mAh/g at a high rate of 1C (1C = 176 mA/g) and 88 mAh/g after 40 cycles with a capacity retention of 85.4%. The SnO2 coating layer endows the NLMO structure with stable ion transport interface to facilitate sodium-ion transfer and an isolated shielding layer to inhibit oxygen loss, thus contributing to stable cycling performance and high capacity even at a high rate. This surface-coating strategy is expected to be applicable to other layered metal oxides as cathode materials to achieve good cycling stability and high-rate capacity. This work is significant for the electrochemical performance improvement of layered metal oxides applied in SIBs.

The influence of Li deficiency: An overlooked factor that determines the anion redox reversibility of Mn-based layered oxide cathodes

The paradigm shift from O3-type structure to O2-type has been extensively proposed as a viable strategy to eliminating/mitigating lattice displacement and voltage decay faced by conventional Li-rich layered oxides. However, the influence of Li deficiency in pristine structure on the reversibility of anionic redox has been overlooked. Herein, we demonstrate that the O2-type structure is not always a better choice in achieving stable anionic redox than that of the O3-type Mn-based layered oxides by investigating two closely related O2- and O3-Li0.6[Li0.2Mn0.8]O2 materials with plenty of Li deficiency in pristine structure. Through the suites of characterizations including Mn K-edge XANES/EXAFS, 7Li pj-MATPASS NMR and Raman spectroscopies, we substantiate the poorer reversibility of the local structural transformation around Mn and Li upon cycling for O2-Li0.6[Li0.2Mn0.8]O2 in comparison with that of O3-Li0.6[Li0.2Mn0.8]O2 (within 2.0–4.8 V). Besides, irreversible out-of-plane transition metal migration occurs in O2-Li0.6[Li0.2Mn0.8]O2 while such process is dramatically suppressed in O3-Li0.6[Li0.2Mn0.8]O2. Our results indicate that in addition to the oxygen stacking sequence, the Li deficiency in pristine structure is also a decisive factor that influences the reversibility of anionic redox in layered oxides.

Mitigating the P2–O2 phase transition of Ni–Co–Mn based layered oxide for improved sodium-ion batteries via interlayered structural modulation

Mn-based layered oxides are promising cathode materials for sodium-ion batteries owing to their high reversible capacities. However, P2–O2 phase transition and Jahn–Teller distortion of Mn3+ frequently occur at the end of the discharging process, resulting in low cycling stability and severe capacity degradation during the cycling processes. In this study, we proposed an effective strategy to inhibit the harmful phase transition and suppress the Jahn–Teller distortion using Al substitution. The proposed method was validated via in situ and ex situ X-ray diffraction. Furthermore, the Al-substituted P2-Na0.7Ni0.2Co0.2Mn0.58Al0.02O2(NCMA2) electrode exhibited only a topotactic phase transition from P2 to OP4 and excellent cycling stability (80% retention of the initial capacity at 170 mAh/g after 50 cycles at 0.1 C within 1.50–4.50 V). X-ray photoelectron spectroscopy analysis showed that the Mn4+ content of the Al-substituted electrode was higher than the bare NCM (Na0.7Ni0.2Co0.2Mn0.6O2) electrode in both the charge and discharge states. This confirms that Al substitution can improve the electrochemical performance by mitigating the irreversible P2–O2 phase transition and suppressing Jahn–Teller distortion. This study provides a new perspective for effectively mitigating the P2–O2 phase transition in Mn-based layered oxide cathodes via interlayered structural modulation.

Promoting reversibility of layered potassium cathode through interstitial doping

With the increasing needs for large-scale and low-cost energy storage devices, Mn-based layered oxide cathodes have achieved considerable researching interests for potassium-ion batteries owing to their high energy density, abundant resource and low toxicity. However, their developments are challenged by the absence of suitable cathode materials to tolerate large-sized K-ion insertion/extraction and the presence of Jahn-Teller distortion of Mn3+. To address this issue, we present a strategy of embedding boron into interstitial tetrahedral sites to obtain a P3-K0.5Mn0.8Co0.2B0.1O2 cathode. Strong B-O covalent bonds facilitate the construction of robust orthorhombic framework and alleviate the undesired elongation of Mn-O bonds, contributing to excellent electrochemical performance. In addition, boron ions are verified to promote the formation of a homogeneous cathode electrolyte interphase layer, improving interfacial stability and realizing highly reversible cycling in a wide voltage range (1.4–4.3 V). This strategy provides a new pathway towards the development of high-performance cathode materials for potassium-ion batteries.

Regulating Anionic Redox via Mg Substitution in Mn-Rich Layered Oxide Cathodes Enabling High Electrochemical Stability for Sodium-Ion Batteries.

With the limited resources and high cost of lithium-ion batteries (LIBs) and the ever-increasing market demands, sodium-ion batteries (SIBs) gain much interest due to their economical sustainability, and similar chemistry and manufacturing processes to LIBs. As cathodes play a vital role in determining the energy density of SIBs, Mn-based layered oxides are promising cathodes due to their low cost, environmental friendliness, and high theoretical capacity. However, the main challenge is structural instability upon cycling at high voltage. Herein, Mg is introduced into the P2-type Na0.62 Ni0.25 Mn0.75 O2 cathode to enhance electrochemical stability. By combining electrochemical testing and material characterizations, it is found that substituting 10 mol% Mg can effectively alleviate the P2-O2 phase transition, Jahn-Teller distortion, and irreversible oxygen redox. Moreover, structural integrity is greatly improved. These lead to enhanced electrochemical performances. With the optimized sample, a remarkable capacity retention of 92% in the half cell after 100 cycles and 95% in the full cell after 170 cycles can be achieved. Altogether, this work provides an alternative way to stabilize P2-type Mn-based layer oxide cathodes, which in turn, put forward the development of this material for the next-generation SIBs.

Cross-sectional transmission electron microscopy studies of Si coated heat-treated stainless steel with improved optical absorption for solar thermal applications

Heat-treatment of stainless steel substrate is reported to improve absorptance due to an increase in roughness along with the formation of surface oxides. Depositing a thin Si layer on stainless steel prior to the heat-treatment results in the formation of islands of nano-micrometer sizes with gaps between them which helps in improving absorptance. Cross-sectional Transmission Electron Microscopy studies are required to understand the development of the surface structures and improved optical properties. The cross-sectional bright- and dark-field Transmission Electron Microscopy images showed the presence of a bright Si-rich region where small nanocrystalline islands were embedded. On top of this layer, larger nanocrystalline protrusions were observed. Energy Dispersive X-ray analysis and Selected Area Diffraction data showed that the substrate elements diffuse out through the Si layer forming smaller islands of various Fe-Cr-Mn-based silicides in the Si layer and islands of Fe, Cr, and Mn-based silicides and oxides at the surface. The High-Resolution Transmission Electron Microscopy images showed that the islands are nanocrystalline in nature and are embedded in a Si-rich amorphous region. The absence of O in the Si-rich layer in SAD data was observed. Also, from the top layer EDX data, Fe peak intensity was found to be higher than Cr peak intensity. These observations indicate that the presence of the Si layer helps in reducing the inward diffusion of O into the substrate, thus preventing internal oxidation. Also, this Si layer prevents the Cr from forming a continuous Cr oxide layer and instead forms mixed oxide/silicide islands which enhance optical properties. Similar studies in the heat-treated substrate without a Si layer showed the presence of sharp-angled nanocrystalline structures of Fe-Cr-based oxides and smooth-angled nanocrystalline structures of Fe-Mn-based oxides on the surface.

Entropy-Stabilized Layered K0.6Ni0.05Fe0.05Mg0.05Ti0.05Mn0.725O2 as a High-Rate and Stable Cathode for Potassium-Ion Batteries.

Mn-based layered oxides have been considered the most promising cathode candidates for cost-effective potassium-ion batteries (PIBs). Herein, equiatomic constituents of Ni, Fe, Mg, and Ti have been introduced into the transition metal layers of Mn-based layered oxide to design a high-entropy K0.6Ni0.05Fe0.05Mg0.05Ti0.05Mn0.0725O2 (HE-KMO, S = 1.17R). Consequently, the experimental results manifest that the layered structure of HE-KMO is more stable than conventional low-entropy K0.6MnO2 (LE-KMO, S = 0.66R) during successive cycling and even upon exposure to moisture. Diffraction and electrochemical measurements reveal that HE-KMO undergoes a solid-solution mechanism, contrary to the multistage phase transition processes typically exemplified in K0.6MnO2. Benefiting from the stabilized high-entropy layered framework and the solid-solution K+ storage mechanism, the entropy-stabilized HE-KMO not only demonstrates exceptional rate capability but also shows excellent cyclic stability. Notably, a capacity retention ratio of 86% after 3000 cycles can still be sustained at a remarkable current density of 5000 mA g-1.

Phase-engineering modulation of Mn-based oxide cathode for constructing super-stable sodium storage

The Mn-based oxide cathode with enriched crystal phase structure and component diversity can provide the excellent chemistry structure for Na-ion batteries. Nevertheless, the broad application prospect is obstructed by the sluggish Na+ kinetics and the phase transitions upon cycling. Herein, we establish the thermodynamically stable phase diagram of various Mn-based oxide composites precisely controlled by sodium content tailoring strategy coupling with co-doping and solid-state reaction. The chemical environment of the P2/P'3 and P2/P3 biphasic composites indicate that the charge compensation mechanism stems from the cooperative contribution of anions and cations. Benefiting from the no phase transition to scavenge the structure strain, P2/P'3 electrode can deliver long cycling stability (capacity retention of 73.8 % after 1000 cycles at 10 C) and outstanding rate properties (the discharge capacity of 84.08 mA h g−1 at 20 C) than P2/P3 electrode. Furthermore, the DFT calculation demonstrates that the introducing novel P'3 phase can significantly regulate the Na+ reaction dynamics and modify the local electron configuration of Mn. The effective phase engineering can provide a reference for designing other high-performance electrode materials for Na-ion batteries.

Comparing Mn-based oxides filters started by KMnO4 versus K2FeO4 for ammonium and manganese removal: Formation mechanism of active species

A pilot-scale filtration system was adopted to prepare filter media with catalytic activity to remove manganese (Mn2+) and ammonium (NH4+-N). Three different combinations of oxidants (KMnO4 and K2FeO4) and reductants (MnSO4 and FeCl2) were used during the start-up period. Filter R3 started up by KMnO4 and FeCl2 (Mn7+→MnOx) exhibited excellent catalytic property, and the NH4+-N and Mn2+ removal efficiency reached over 80% on the 10th and 35th days, respectively. Filter R1 started up by K2FeO4 and MnSO4 (MnOx←Mn2+) exhibited the worst catalytic property. Filter R2 started up by KMnO4 and MnSO4 (Mn7+→MnOx←Mn2+) were in between. According to Zeta potential results, the Mn-based oxides (MnOx) formed by Mn7+→MnOx performed the highest pHIEP and pHPZC. The higher the pHIEP and pHPZC, the more unfavorable the cation adsorption. However, it was inconsistent with its excellent Mn2+ and NH4+-N removal abilities, implying that catalytic oxidation played a key role. Combined with XRD and XPS analysis, the results showed that the MnOx produced by the reduction of KMnO4 showed early formation of buserite crystals, high degree of amorphous, high content of Mn3+ and lattice oxygen with the higher activity to form defects. The above results showed that MnOx produced by the reduction of KMnO4 was more conducive to the formation of active species for catalytic oxidation of NH4+-N and Mn2+ removal. This study provides new insights on the formation mechanisms of the active MnOx that could catalytic oxidation of NH4+-N and Mn2+.

Zr/Ti trace Co-doping induced disordered structure to enhance the cycling stability of Li-rich Mn-based layered oxide cathodes

Due to the ultrahigh energy density, Li-rich Mn-based layered oxide cathodes have attracted great attentions. However, the irreversible structural transformation usually leads to long-cycled capacity decay, which severely restricts their practical applications. Here, a Zr/Ti trace co-doping strategy is proposed to stabilize the structure and obtain excellent electrochemical performance by constructing bulk phase disorder and surface Zr-enriched structures. The designed Li1.2Mn0.53Ni0.13Co0.13Zr0.005Ti0.005O2 (ZT-LRM) not only shows a higher specific capacity but also achieves an excellent long-cycle performance. The capacity retention of ZT-LRM is 69 % after 500 cycles at 5C (1250 mA g−1), which is much higher than that (34 %) of the Li1.2Mn0.54Ni0.13Co0.13O2 cathode. Neutron powder diffraction and transmission electron microscopy are used to demonstrate the disordered structure in the particles and the line scanning proves the surface Zr enrichment. In-situ X-ray diffraction verifies the more stable structural evolutions of the ZT-LRM during cycling. This simple modification method provides a reference for commercial applications of Li-rich Mn-based layered oxide cathodes.

Investigations on substituted Si-doped Mn2O3/Mn3O4 redox pair for thermochemical energy storage

Next-generation concentrated solar power plants with thermochemical energy storage can meet the demand for peak regulation and power supply, which stimulates the development and application of low-priced metal oxide thermochemical thermal storage materials. Mn-based composite metal oxide is a competitive candidate for large-scale applications given its character of being non-toxic, cheap, and highly efficient. However, the utilization of pure Mn2O3 suffers from sintering, which limits its re-oxidation and hence affects the applicability. In this study, Si is introduced to solve the above problems and improve the reaction characteristics of pure Mn2O3. (Mn1−xSix)2O3 is synthesized by substituent doping, with the best performance at x = 3 % and 5 %, reaching 96.18 % and 94.71 % of reduction conversion rate, respectively. The performance decay of the (Mn0.95Si0.05)2O3 sample was tested and evaluated, with reduction conversions of 90.92 % and 63.64 % after 50 and 300 cycles, respectively. A series of characterization results confirm that Si4+ is successfully doped into the Mn2O3 lattice, introducing defects into the crystal structure, which is favorable for the oxidation reaction. Density functional theory calculations of oxygen adsorption/dissociation and oxygen diffusion indicate that the doped Mn-Si oxides have lower reaction potentials and energies, which explains the promotion of the re-oxidation reaction by Si. By investigating the thermochemical energy storage properties and mechanism of Mn-Si composite metal oxides, we provide guidance for large-scale, cheap, and eco-friendly energy storage applications.

Stable high-voltage operation of oxygen redox in P2-type Na-layered oxide cathode at fast discharging via enhanced kinetics

Sluggish kinetics and structural instability caused by oxygen redox can lead to poor electrochemical performance of cathode materials, resulting in a much lower operating voltage during discharging than charging (especially at high current densities) and poor power-capability. Additionally, undesirable phase transitions during charge/discharge negatively affect the electrochemical performance of oxygen-redox-based P2-type Mn-based layered oxide cathodes. In this study, we demonstrate the successful stabilization of oxygen redox in P2-type Mn-based layered oxide cathodes through the synergy of Cu-Co. Particularly, the discharge operation voltage and energy density during fast charging are significantly enhanced. The average discharge voltage difference of P2-type Na0.67[Cu0.2Co0.2Mn0.6]O2 between 10 and 1000 mA g−1 is approximately ∼0.18 V, respectively, which is distinctly different from the case of P2-type Na0.67[Cu0.2Mn0.8]O2 showing differences of approximately ∼0.36 V under the same conditions. Moreover, after 100 cycles, the discharge capacity of P2-type Na0.67[Cu0.2Co0.2Mn0.6]O2 with oxygen redox is retained to ∼93% of the initial capacity, due to both a small volume change during charge/discharge (∼0.6%) and successful suppression of undesirable phase transition of P2-OP4. The outcomes of this study underscore the viability of employing oxygen-redox-based P2-type Na-layered oxide as a reasonable method for achieving exceptional high-rate and high-voltage performance.

Rational construction of graphitic carbon nitride composited Li-rich Mn-based oxide cathode materials toward high-performance Li-ion battery

Li-rich Mn-based oxides (LRMOs) are considered as one of the most-promising cathode materials for next generation Li-ion batteries (LIBs) because of their high energy density. Nevertheless, the intrinsic shortcomings, such as the low first coulomb efficiency, severe capacity/voltage fade, and poor rate performance seriously limit its commercial application in the future. In this work, we construct successfully g-C3N4 coating layer to modify Li1.2Mn0.54Ni0.13Co0.13O2 (LMNC) via a facile solution. The g-C3N4 layer can alleviate the side-reaction between electrolyte and LMNC materials, and improve electronic conduction of LMNC. In addition, the g-C3N4 layer can suppress the collapse of structure and improve cyclic stability of LMNC materials. Consequently, g-C3N4 (4 wt%)-coated LMNC sample shows the highest initial coulomb efficiency (78.5%), the highest capacity retention ratio (78.8%) and the slightest voltage decay (0.48 V) after 300 loops. Besides, it also can provide high reversible capacity of about 300 and 93 mAh g−1 at 0.1 and 10C, respectively. This work proposes a novel approach to achieve next-generation high-energy density cathode materials, and g-C3N4 (4 wt%)-coated LMNC shows an enormous potential as the cathode materials for next generation LIBs with excellent performance.