Exposing {010} Active Facets by Multiple‐Layer Oriented Stacking Nanosheets for High‐Performance Capacitive Sodium‐Ion Oxide Cathode

As one of the most promising cathodes for rechargeable sodium‐ion batteries (SIBs), O3‐type layered transition metal oxides commonly suffer from inevitably complicated phase transitions and sluggish kinetics. Here, a Na[Li_0.05Ni_0.3Mn_0.5Cu_0.1Mg_0.05]O₂ cathode material with the exposed {010} active facets by multiple‐layer oriented stacking nanosheets is presented. Owing to reasonable geometrical structure design and chemical substitution, the electrode delivers outstanding rate performance (71.8 mAh g^?1 and 16.9 kW kg^?1 at 50C), remarkable cycling stability (91.9% capacity retention after 600 cycles at 5C), and excellent compatibility with hard carbon anode. Based on the combined analyses of cyclic voltammograms, ex situ X‐ray absorption spectroscopy, and operando X‐ray diffraction, the reaction mechanisms behind the superior electrochemical performance are clearly articulated. Surprisingly, Ni²⁺/Ni³⁺ and Cu²⁺/Cu³⁺ redox couples are simultaneously involved in the charge compensation with a highly reversible O3–P3 phase transition during charge/discharge process and the Na⁺ storage is governed by a capacitive mechanism via quantitative kinetics analysis. This optimal bifunctional regulation strategy may offer new insights into the rational design of high‐performance cathode materials for SIBs.     

Rational Design of Na(Li1/3Mn2/3)O2 Operated by Anionic Redox Reactions for Advanced Sodium‐Ion Batteries

In an effort to develop high‐energy‐density cathodes for sodium‐ion batteries (SIBs), low‐cost, high capacity Na(Li_1/3Mn_2/3)O₂ is discovered, which utilizes the labile O 2p‐electron for charge compensation during the intercalation process, inspired by Li₂MnO₃ redox reactions. Na(Li_1/3Mn_2/3)O₂ is systematically designed by first‐principles calculations considering the Li/Na mixing enthalpy based on the site preference of Na in the Li sites of Li₂MnO₃. Using the anionic redox reaction (O^2?/O^?), this Mn‐oxide is predicted to show high redox potentials (≈4.2 V vs Na/Na⁺) with high charge capacity (190 mAh g^?1). Predicted cathode performance is validated by experimental synthesis, characterization, and cyclic performance studies. Through a fundamental understanding of the redox reaction mechanism in Li₂MnO₃, Na(Li_1/3Mn_2/3)O₂ is designed as an example of a new class of promising cathode materials, Na(Li_1/3M_2/3)O₂ (M: transition metals featuring stabilized M⁴⁺), for further advances in SIBs.     

Li-substituted P2-Na0.66LixMn0.5Ti0.5O2 as an advanced cathode material and new “bi-functional” electrode for symmetric sodium-ion batteries

In this study, we have introduced the layered materials P2-Na_0.66Li_xMn_0.5Ti_0.5O₂ as cathode materials for sodium ion batteries (SIBs), and then P2-Na_0.66Li_xMn_0.5Ti_0.5O₂ was employed as bi-functional electrode in SIBs. The structural stability and electrochemical properties of P2-Na_0.66Li_xMn_0.5Ti_0.5O₂ were promoted by inserting lithium. The Na_0.66Li_0.2Mn_0.5Ti_0.5O₂ as a cathode material can exhibit a reversible discharge capacity of 128?mA?h?g^?1 at 0.1C after 100 cycles, and even deliver 72?mA?h?g^?1 at 5C. Interestingly, the P2-Na_0.66Li_0.2Mn_0.5Ti_0.5O₂ is studied as a “bi-functional” active material for symmetric sodium-ion batteries. This novel symmetric full cell exhibits 65?mA?h?g^?1 at a current density of 20?mA?g^?1.     

Spray-drying synthesis of P2-Na2/3Fe1/2Mn1/2O2 with improved electrochemical properties

Owing to its high theoretical capacity, P2-type Na_2/3Fe_1/2Mn_1/2O₂ has been considered as a kind of promising cathode material. However, the practical application is limited due to excessively high calcining temperature during traditional preparation processes. Here, we report the synthesis of P2-Na_2/3Fe_1/2Mn_1/2O₂ by using a facile spray-drying method followed by calcining at low temperature. Under the optimal conditions, the well-crystallized P2-Na_2/3Fe_1/2Mn_1/2O₂ material with excellent rate capability and cycle ability is obtained. And the sample exhibits the initial discharge capacities of 217.9, 171.3 and 117.4 mAh g⁻¹ at 0.1 C, 0.5 C and 2 C rate, respectively. The developed Na_2/3Fe_1/2Mn_1/2O₂ material, synthesized by a new spray drying-calcining procedure, may potentially be used as a suitable cathode in sodium ion batteries.     

Weak-Coordination Electrolyte Enabling Fast Li+ Transport in Lithium Metal Batteries at Ultra-Low Temperature

Lithium metal batteries (LMBs) are promising for next-generation high-energy-density batteries owing to the highest specific capacity and the lowest potential of Li metal anode. However, the LMBs are normally confronted with drastic capacity fading under extremely cold conditions mainly due to the freezing issue and sluggish Li⁺ desolvation process in commercial ethylene carbonate (EC)-based electrolyte at ultra-low temperature (e.g., below −30 °C). To overcome the above challenges, an anti-freezing carboxylic ester of methyl propionate (MP)-based electrolyte with weak Li⁺ coordination and low-freezing temperature (below −60 °C) is designed, and the corresponding LiNi_0.8Co_0.1Mn_0.1O₂ (NCM811) cathode exhibits a higher discharge capacity of 84.2 mAh g⁻¹ and energy density of 195.0 Wh kg⁻¹_cathode than that of the cathode (1.6 mAh g⁻¹ and 3.9 Wh kg⁻¹_cathode) working in commercial EC-based electrolytes for NCM811‖ Li cell at −60 °C. Molecular dynamics simulation, Raman spectra, and nuclear magnetic resonance characterizations reveal that rich mobile Li⁺ and the unique solvation structure with weak Li⁺ coordination are achieved in MP-based electrolyte, which collectively facilitate the Li⁺ transference process at low temperature. This work provides fundamental insights into low-temperature electrolytes by regulating solvation structure, and offers the basic guidelines for the design of low-temperature electrolytes for LMBs.     

Co-Construction of Sulfur Vacancies and Heterojunctions in Tungsten Disulfide to Induce Fast Electronic/Ionic Diffusion Kinetics for Sodium-Ion Batteries

Engineering novel electrode materials with unique architectures has a significant impact on tuning the structural/electrochemical properties for boosting the performance of secondary battery systems. Herein, starting from well-organized WS₂ nanorods, an ingenious design of a one-step method is proposed to prepare a bimetallic sulfide composite with a coaxial carbon coating layer, simply enabled by ZIF-8 introduction. Rich sulfur vacancies and WS₂/ZnS heterojunctions can be simultaneously developed, that significantly improve ionic and electronic diffusion kinetics. In addition, a homogeneous carbon protective layer around the surface of the composite guarantees an outstanding structural stability, a reversible capacity of 170.8 mAh g⁻¹ after 5000 cycles at a high rate of 5 A g⁻¹. A great potential in practical application is also exhibited, where a full cell based on the WS_2−x/ZnS@C anode and the P2-Na_2/3Ni_1/3Mn_1/3O₂ cathode can maintain a reversible capacity of 89.4 mAh g⁻¹ after 500 cycles at 1 A g⁻¹. Moreover, the underlying electrochemical Na storage mechanisms are illustrated in detail by theoretical calculations, electrochemical kinetic analysis, and operando X-ray diffraction characterization.     

A Garnet-Type Solid-Electrolyte-Based Molten Lithium−Molybdenum−Iron(II) Chloride Battery with Advanced Reaction Mechanism

Solid-electrolyte-based molten-metal batteries have attracted considerable attention for grid-scale energy storage. Although ZEBRA batteries are considered one of the promising candidates, they still have the potential concern of metal particle growth and ion exchange with the β”-Al₂O₃ electrolyte. Herein, a Li_6.4La₃Zr_1.4Ta_0.6O₁₂ solid-electrolyte-based molten lithium−molybdenum−iron(II) chloride battery (denoted as Li−Mo−FeCl₂) operated at temperature of 250 °C, comprising a mixture of Fe and LiCl cathode materials, a Li anode, a garnet-type Li-ion ceramic electrolyte, and Mo additive, is designed to overcome these obstacles. Different from conventional battery reaction mechanisms, this battery revolutionarily synchronizes the reversible Fe−Mo alloying−dealloying reactions with the delithiation−lithiation processes, meaning that the porous Mo framework derived from Fe−Mo alloy simultaneously suppresses the growth of pure Fe particles. By adopting a Li anode and a Li-ion ceramic electrolyte, the corrosion problem between the cathode and the solid electrolyte is overcome. With similar battery cost ($12 kWh⁻¹), the theoretical energy density of Li−Mo−FeCl₂ battery surpasses that of a Na−FeCl₂ ZEBRA battery over 25%, to 576 Wh kg⁻¹ and 2216 Wh L⁻¹, respectively. Experimental results further prove this cell has excellent cycling performance (472 mAh g_LiCl⁻¹ after 300 cycles, 50 mg active material) and strong tolerance against the overcharge−overdischarge (3−1.6 V) and freezing−thawing (25−250 °C) incidents.     

MOF-Derived Mn2O3 Nanocage with Oxygen Vacancies as Efficient Cathode Catalysts for Li–O2 Batteries

Designing efficient and cost-effective electrocatalysts is the primary imperative for addressing the pivotal concerns confronting lithium–oxygen batteries (LOBs). The microstructure of the catalyst is one of the key factors that influence the catalytic performance. This study proceeds to the advantage of metal-organic frameworks (MOFs) derivatives by annealing manganese 1,2,3-triazolate (MET-2) at different temperatures to optimize Mn₂O₃ crystals for special microstructures. It is found that at 350 °C annealing temperature, the derived Mn₂O₃ nanocage maintains the structure of MOF, the inherited high porosity and large specific surface area provide more channels for Li⁺ and O₂ diffusion, beside the oxygen vacancies on the surface of Mn₂O₃ nanocages enhance the electrocatalytic activity. With the synergy of unique structure and rich oxygen vacancies, the Mn₂O₃ nanocage exhibits ultrahigh discharge capacity (21 070.6 mAh g⁻¹ at 500 mA g⁻¹) and excellent cycling stability (180 cycles at the limited capacity of 600 mAh g⁻¹ with a current of 500 mA g⁻¹). This study demonstrates that the Mn₂O₃ nanocage structure containing oxygen vacancies can significantly enhance catalytic performance for LOBs, which provide a simple method for structurally designed transition metal oxide electrocatalysts.     

Role of Redox‐Inactive Transition‐Metals in the Behavior of Cation‐Disordered Rocksalt Cathodes

Owing to the capacity boost from oxygen redox activities, Li‐rich cation‐disordered rocksalts (LRCDRS) represent a new class of promising high‐energy Li‐ion battery cathode materials. Redox‐inactive transition‐metal (TM) cations, typically d⁰ TM, are essential in the formation of rocksalt phases, however, their role in electrochemical performance and cathode stability is largely unknown. In the present study, the effect of two d⁰ TM (Nb⁵⁺ and Ti⁴⁺) is systematically compared on the redox chemistry of Mn‐based model LRCDRS cathodes, namely Li_1.3Nb_0.3Mn_0.4O₂ (LNMO), Li_1.25Nb_0.15Ti_0.2Mn_0.4O₂ (LNTMO), and Li_1.2Ti_0.4Mn_0.4O₂ (LTMO). Although electrochemically inactive, d⁰ TM serves as a modulator for oxygen redox, with Nb⁵⁺ significantly enhancing initial charge storage contribution from oxygen redox. Further studies using differential electrochemical mass spectroscopy and resonant inelastic X‐ray scattering reveal that Ti⁴⁺ is better in stabilizing the oxidized oxygen anions (O^n?, 0 < n < 2), leading to a more reversible O redox process with less oxygen gas release. As a result, much improved chemical, structural and cycling stabilities are achieved on LTMO. Detailed evaluation on the effect of d⁰ TM on degradation mechanism further suggests that proper design of redox‐inactive TM cations provides an important avenue to balanced capacity and stability in this newer class of cathode materials.     

Surface modification with oxygen vacancy in Li-rich layered oxide Li1.2Mn0.54Ni0.13Co0.13O2 for lithium-ion batteries

A couple of layered Li-rich cathode materials Li_1.2Mn_0.54Ni_0.13Co_0.13O₂ without any carbon modification are successfully synthesized by solvothermal and hydrothermal methods followed by a calcination process. The sample synthesized by the solvothermal method (S-NCM) possesses more homogenous microstructure, lower cation mixing degree and more oxygen vacancies on the surface, compared to the sample prepared by the hydrothermal method (H-NCM). The S-NCM sample exhibits much better cycling performance, higher discharge capacity and more excellent rate performance than H-NCM. At 0.2 C rate, the S-NCM sample delivers a much higher initial discharge capacity of 292.3 mAh g⁻¹ and the capacity maintains 235 mAh g⁻¹ after 150 cycles (80.4% retention), whereas the corresponding capacity values are only 269.2 and 108.5 mAh g⁻¹ (40.3% retention) for the H-NCM sample. The S-NCM sample also shows the higher rate performance with discharge capacity of 118.3 mAh g⁻¹ even at a high rate of 10 C, superior to that (46.5 mAh g⁻¹) of the H-NCM sample. The superior electrochemical performance of the S-NCM sample can be ascribed to its well-ordered structure, much larger specific surface area and much more oxygen vacancies located on the surface.     

O3‐Type Layered Ni‐Rich Oxide: A High‐Capacity and Superior‐Rate Cathode for Sodium‐Ion Batteries

Inspired by its high‐active and open layered framework for fast Li⁺ extraction/insertion reactions, layered Ni‐rich oxide is proposed as an outstanding Na‐intercalated cathode for high‐performance sodium‐ion batteries. An O3‐type Na_0.75Ni_0.82Co_0.12Mn_0.06O₂ is achieved through a facile electrochemical ion‐exchange strategy in which Li⁺ ions are first extracted from the LiNi_0.82Co_0.12Mn_0.06O₂ cathode and Na⁺ ions are then inserted into a layered oxide framework. Furthermore, the reaction mechanism of layered Ni‐rich oxide during Na⁺ extraction/insertion is investigated in detail by combining ex situ X‐ray diffraction, X‐ray photoelectron spectroscopy, and electron energy loss spectroscopy. As an excellent cathode for Na‐ion batteries, O3‐type Na_0.75Ni_0.82Co_0.12Mn_0.06O₂ delivers a high reversible capacity of 171 mAh g^?1 and a remarkably stable discharge voltage of 2.8 V during long‐term cycling. In addition, the fast Na⁺ transport in the cathode enables high rate capability with 89 mAh g^?1 at 9 C. The as‐prepared Ni‐rich oxide cathode is expected to significantly break through the limited performance of current sodium‐ion batteries.     

Zinc-Doping Strategy on P2-Type Mn-Based Layered Oxide Cathode for High-Performance Potassium-ion Batteries

Mn-based layered oxide is extensively investigated as a promising cathode material for potassium-ion batteries due to its high theoretical capacity and natural abundance of manganese. However, the Jahn–Teller distortion caused by high-spin Mn³⁺(t_2g³e_g¹) destabilizes the host structure and reduces the cycling stability. Here, K_0.02Na_0.55Mn_0.70Ni_0.25Zn_0.05O₂ (denoted as KNMNO-Z) is reported to inhibit the Jahn–Teller effect and reduce the irreversible phase transition. Through the implementation of a Zn-doping strategy, higher Mn valence is achieved in the KNMNO-Z electrode, resulting in a reduction of Mn³⁺ amount and subsequently leading to an improvement in cyclic stability. Specifically, after 1000 cycles, a high retention rate of 97% is observed. Density functional theory calculations reveals that low-valence Zn²⁺ ions substituting the transition metal position of Mn regulated the electronic structure around the Mn O bonding, thereby alleviating the anisotropic coupling between oxidized O²⁻ and Mn⁴⁺ and improving the structural stability. K_0.02Na_0.55Mn_0.70Ni_0.25Zn_0.05O₂ provided an initial discharge capacity of 57 mAh g⁻¹ at 100 mA g⁻¹ and a decay rate of only 0.003% per cycle, indicating that the Zn-doped strategy is effective for developing high-performance Mn-based layered oxide cathode materials in PIBs.     

Realization of a 594 Wh kg−1 Lithium-Metal Battery Using a Lithium-Free V2O5 Cathode with Enhanced Performances by Nanoarchitecturing

To realize a high-energy lithium metal battery (LMB) using a high-capacity Li-free cathode, in this work, nanoplate-stacked V₂O₅ with dominantly exposed (010) facets and a relatively short [010] length is proposed to be used as a cathode. The V₂O₅ nanostructure can be fabricated via a modified hydrothermal method, including a Li⁺ crystallization inhibitor, followed by heat treatment. In particular, the enlargement of the favorable Li⁺ diffusion pathway in the [010] direction and the formation of a robust hierarchical nanoplate-stacked structure in the modified V₂O₅ improves the electrochemical kinetics and stability; as a result, the nanoplate-stacked V₂O₅ electrode exhibits a higher capacity and rate performance (258 mAh g⁻¹ at 50 mA g⁻¹ [0.17 C], 140 mAh g⁻¹ at 1 A g⁻¹ [3.4 C]) and cycling capability (79% capacity retention after 100 cycles at 0.5 C) compared to the previously reported V₂O₅ nanobelt electrode. Notably, the LMB composed of Li//nanoplate-stacked V₂O₅ full-cells shows high specific energy densities of 594.1 and 296.2 Wh kg⁻¹ at 0.1 and 1.0 C, respectively, and a high Coulombic efficiency of 99.6% during 50 cycles.     

A Novel NASICON-Type Na4MnCr(PO4)3 Demonstrating the Energy Density Record of Phosphate Cathodes for Sodium-Ion Batteries

Sodium-ion batteries (SIBs) have attracted incremental attention as a promising candidate for grid-scale energy-storage applications. To meet practical requirements, searching for new cathode materials with high energy density is of great importance. Herein, a novel Na superionic conductor (NASICON)-type Na₄MnCr(PO₄)₃ is developed as a high-energy cathode for SIBs. The Na₄MnCr(PO₄)₃ nanoparticles homogeneously embedded in a carbon matrix can present an extraordinary reversible capacity of 160.5 mA h g⁻¹ with three-electron reaction at ≈3.53 V during the Na⁺ extraction/insertion process, realizing an unprecedentedly high energy density of 566.5 Wh kg⁻¹ in the phosphate cathodes for SIBs. It is intriguing to reveal the underlying mechanism of the unique Mn²⁺/Mn³⁺, Mn³⁺/Mn⁴⁺, and Cr³⁺/Cr⁴⁺ redox couples via X-ray absorption near-edge structure spectroscopy. The whole electrochemical reaction undergoes highly reversible single-phase and biphasic transitions with a moderate volume change of 7.7% through in situ X-ray diffraction and ex situ high-energy synchrotron X-ray diffraction. Combining density functional theory (DFT) calculations with the galvanostatic intermittent titration technique, the superior performance is ascribed to the low ionic-migration energy barrier and desirable Na-ion diffusion kinetics. The present work can offer a new insight into the design of multielectron-reaction cathode materials for SIBs.     

Fabrication and electrochemical characterization of a novel spinel Li2Ni0.5Mn1.5O4 cathode coated with conductive glass for Lithium-ions batteries

A new spinel Li₂Ni_0.5Mn_1.5O₄ (LNMO) cathode reported in our previous work displays high initial specific capacity (260.4 mAh g^?1) and good coulombic efficiency (92.2%), but suffers from low capacity retention of 80.2% after 50 cycles. In this paper, Li₂O-0.2B₂O₃-1.8SiO₂ (LBSO) glass phase surface modification is adopted to promote the electrochemical performance of LNMO. LBSO layer coated on the surface of LNMO cathode, as confirmed by SEM and HRTEM observation, can effectively prevent the cathode from dissolving in the electrolyte, therefore suppresses the increase in resistance and the degradation in Li-ions diffusion. Consequently, the electrochemical properties of the surface modified cathode material are improved. The initial specific capacity of 0.3 wt% LBSO coated LNMO is kept as 263 mAh g^?1 with coulombic efficiency of 95%. Notably, the capacity retention after 100 cycles is improved from 69% to 83% by a comparison between the pristine and coated samples. Moreover, the coated cathode exhibits good rate performance, giving high specific capacity of 142 mAh g^?1 even at a current density of 5C. All the results presented above suggest high potential for the material as candidate cathode for high energy density batteries.     

Boosting Li–O2 Battery Performance via Coupling of P–N Site-Rich N,P Co-Doped Graphene-Like Carbon Nanosheets with Nano-CePO4

Development of efficient and robust cathode catalysts is critical for the commercialization of Li-O₂ batteries (LOBs). Herein, a well-designed CePO₄@N-P-CNSs cathode catalyst for LOBs via coupling P-N site-rich N, P co-doped graphene-like carbon nanosheets (N-P-CNSs) with nano-CePO₄ via a novel “in situ derivation” coupling strategy by in situ transforming the P atoms of P-C sites in N-P-CNSs to CePO₄ is reported. The CePO₄@N-P-CNSs exhibit superior bifunctional ORR/OER activity relative to commercial Pt/C-RuO₂ with an overall overpotential of 0.64 V (vs RHE). Moreover, the LOB with CePO₄@N-P-CNSs as the cathode catalyst delivers a low charge overpotential of 0.67 V (vs Li/Li⁺), high discharge capacity of 29774 mAh g⁻¹ at 100 mA g⁻¹ and long cycling stability of 415 cycles, respectively. The remarkably enhanced LOB performance is attributable to the in situ derived CePO₄ nanoparticles and the P-N sites in N-P-CNSs, which facilitate increased bifunctional ORR/OER activity, promote the rapid and effective decomposition of Li₂O₂ and inhibit the formation of Li₂CO₃. This work may provide new inspiration for designing efficient, durable, and cost-effective cathode catalysts for LOBs.     

A High‐Capacity O2‐Type Li‐Rich Cathode Material with a Single‐Layer Li2MnO3 Superstructure

A high capacity cathode is the key to the realization of high‐energy‐density lithium‐ion batteries. The anionic oxygen redox induced by activation of the Li₂MnO₃ domain has previously afforded an O3‐type layered Li‐rich material used as the cathode for lithium‐ion batteries with a notably high capacity of 250–300 mAh g^?1. However, its practical application in lithium‐ion batteries has been limited due to electrodes made from this material suffering severe voltage fading and capacity decay during cycling. Here, it is shown that an O2‐type Li‐rich material with a single‐layer Li₂MnO₃ superstructure can deliver an extraordinary reversible capacity of 400 mAh g^?1 (energy density: ≈1360 Wh kg^?1). The activation of a single‐layer Li₂MnO₃ enables stable anionic oxygen redox reactions and leads to a highly reversible charge–discharge cycle. Understanding the high performance will further the development of high‐capacity cathode materials that utilize anionic oxygen redox processes.     

Nano-domain structure of Li<Subscript>4</Subscript>Mn<Subscript>5</Subscript>O<Subscript>12</Subscript> spinel

XRD-pure Li₄Mn₅O₁₂ spinels are obtained below 600 °C from oxalate and acetate precursors. The morphology consists of nanometric particles (about 25 nm) with a narrow particle size distribution. HRTEM and electron paramagnetic resonance (EPR) spectroscopy of Mn⁴⁺ are employed for local structure analysis. The HRTEM images recorded on nano-domains in Li₄Mn₅O₁₂ reveal its complex structure. HRTEM shows one-dimensional structure images, which are compatible with the (111) plane of the cubic spinel structure and the (001) plane of monoclinic Li₂MnO₃. For Li₄Mn₅O₁₂ compositions annealed between 400 and 800 °C, EPR spectroscopy shows the appearance of two types of Mn⁴⁺ ions having different metal environments: (i) Mn⁴⁺ ions surrounded by Li⁺ and Mn⁴⁺ and (ii) Mn⁴⁺ ions in Mn⁴⁺-rich environment. The composition of the Li⁺, Mn⁴⁺-shell around Mn⁴⁺ mimics the local environment of Mn⁴⁺ in monoclinic Li₂MnO₃, while the Mn⁴⁺-rich environment is related with that of the spinel phase. The structure of XRD-pure Li₄Mn₅O₁₂ comprises nano-domains with a Li₂MnO₃-like and a Li_4/3−x Mn_5/3+x O₄ composition rather than a single spinel phase with Li in tetrahedral and Li_1/3Mn_5/3 in octahedral spinel sites. The annealing of Li₄Mn₅O₁₂ at temperature higher than 600 °C leads to its decomposition into monoclinic Li₂MnO₃ and spinel Li_4/3−x Mn_5/3+x O₄.     

Lithium insertion into manganese spinels

Lithium has been inserted chemically and electrochemically into Mn₃O₄ and Li[Mn₂]O₄ at room temperature. From X-ray diffraction, it is shown that the [Mn₂]O₄ subarray of the A[B₂]X₄ spinels remains unperturbed and that the electrons compensating for the Li⁺-ion charge reduce Mn³⁺ to Mn²⁺ in Mn₃O₄ and Mn⁴⁺ to Mn³⁺ in Li[Mn₂]O₄. In Li_xMn₃O₄, the tetragonal distortion due to a cooperative Jahn-Teller distortion by octahedral-site Mn³⁺ ions decreases with x from $\text{c}\text{a}\text{= 1.157}$ for x = 0 to $\text{c}\text{a}\text{= 1.054}$ for x = 1. The system Li_1+x[Mn₂]O₄, is cubic at x = 0 and tetragonal ($\text{c}\text{a}\text{= 1.161}$) at x = 1.2. Electrochemical data reveal a two-phase region in the Li_1+xMn₂O₄ system and a maximum x_m = 1.25. X-ray diffraction confirms the coexistence of a cubic and a tetragonal phase in the compositional range 0.1 ≤ x ≤ 0.8. The X-ray data also show that the inserted Li⁺ ions occupy the interstitial octahedral positions of the spinel structure. However, in Li_xMn₃O₄ the tetrahedral-site Mn²⁺ions are displaced from the A positions to the interstitial octahedral positions, as in Li_xFe₃O₄, whereas the tetrahedral-site Li⁺ ions in Li[Mn₂]O₄ remain on the A sites.     

Coupling of Oxygen Vacancies and Heterostructure on Fe3O4 via an Anion Doping Strategy to Boost Catalytic Activity for Lithium-Sulfur Batteries

The sluggish reaction kinetics and severe shutting behaviors of sulfur cathodes are the major roadblocks to realizing the practical application of lithium−sulfur (Li−S) batteries and need to be solved through designing/constructing rational sulfur hosts. Herein, an effective alternative material of Fe₃O_4−x/FeP in-situ embedded in N-doped carbon-tube (Fe₃O_4−x/FeP/NCT) is proposed. In this fabricated heterostructure, NCT skeleton works as a sulfur host provides physical barrier for lithium polysulfides (LiPSs), while Fe₃O_4−x/FeP heterostructure with abundant oxygen vacancies provides double active centers to simultaneously accelerate e⁻/Li⁺ diffusion/transport kinetics and catalysis for LiPSs. Through the respective advantages, Fe₃O_4−x/FeP/NCT exhibits synergy enhancement effect for restraining sulfur dissolution and enhancing its conversion kinetics. Furthermore, the promoted ion diffusion kinetics, enhanced electrical conductivity, and increased active sites of Fe₃O_4−x/FeP/NCT are enabled by oxygen vacancies as well as the heterogeneous interfacial contact, which is clearly confirmed by experimental and first-principles calculations. By virtue of these superiorities, the constructed cathode shows excellent long-term cycling stability and a high-rate capability up to 10 C. Specially, a high areal capacity of 7.2 mAh cm⁻² is also achieved, holding great promise for utilization in advanced Li−S batteries in the future.