Composition‐Tailored 2 D Mn1−xRuxO2 Nanosheets and Their Reassembled Nanocomposites: Improvement of Electrode Performance upon Ru Substitution

Composition‐tailored Mn_1?xRu_xO₂ 2 D nanosheets and their reassembled nanocomposites with mesoporous stacking structure are synthesized by a soft‐chemical exfoliation reaction and the subsequent reassembling of the exfoliated nanosheets with Li⁺ cations, respectively. The tailoring of the chemical compositions of the exfoliated Mn_1?xRu_xO₂ 2 D nanosheets and their lithiated nanocomposites can be achieved by adopting the Ru‐substituted layered manganese oxides as host materials for exfoliation reaction. Upon the exfoliation–reassembling process, the substituted ruthenium ions remain stabilized in the layered Mn_1?xRu_xO₂ lattice with mixed Ru³⁺/Ru⁴⁺ oxidation state. The reassembled Li–Mn_1?xRu_xO₂ nanocomposites show promising pseudocapacitance performance with large specific capacitances of approximately 330 F g^?1 for the second cycle and approximately 360 F g^?1 for the 500th cycle and excellent cyclability, which are superior to those of the unsubstituted Li–MnO₂ homologue and many other MnO₂‐based materials. Electrochemical impedance spectroscopy analysis provides strong evidence for the enhancement of the electrical conductivity of 2 D nanostructured manganese oxide upon Ru substitution, which is mainly responsible for the excellent electrode performance of Li–Mn_1?xRu_xO₂ nanocomposites. The results underscore the powerful role of the composition‐controllable metal oxide 2 D nanosheets as building blocks for exploring efficient electrode materials.     

Developing Intense Blue and Magenta Colors in α‐LiZnBO3: The Role of 3d‐Metal Substitution and Coordination

We describe the synthesis, crystal structures, and optical absorption spectra/colors of 3d‐transition‐metal‐substituted α‐LiZnBO₃ derivatives: α‐LiZn_1?xM^II_xBO₃ (M^II=Co^II (0<x<0.50), Ni^II (0<x≤0.05), Cu^II (0<x≤0.10)) and α‐Li_1+xZn_1?2xM^III_xBO₃ (M^III=Mn^III (0<x≤0.10), Fe^III (0<x≤0.25)). The crystal structure of the host α‐LiZnBO₃, which is both disordered and distorted with respect to Li and Zn occupancies and coordination geometries, is largely retained in the derivatives, which gives rise to unique colors (blue for Co^II, magenta for Ni^II, violet for Cu^II) that could be of significance for the development of new, inexpensive, and environmentally friendly pigment materials, particularly in the case of the blue pigments. Accordingly, this work identifies distorted tetrahedral MO₄ (M=Co, Ni, Cu) structural units, with a long M?O bond that results in trigonal bipyramidal geometry, as new chromophores for blue, magenta, and violet colors in a α‐LiZnBO₃ host. From the L*a*b* color coordinates, we found that Co‐substituted compounds have an intense blue color that is stronger than that of CoAl₂O₄ and YIn_0.90Mn_0.10O₃. The near‐infrared (NIR) reflectance spectral studies indicate that these compounds exhibit a moderate IR reflectivity that could be significant for applications as “cool pigments”.     

Lithium-substituted cobalt oxide spinels LixM1−xCo2O4 (M = Co2+, Zn2+; 0 ≤ x ≤ 0.4)

Substitution of Li⁺ into Co₃O₄ and ZnCo₂O₄ gives rise to the solid solution series Li_xM_1?xCo₂O₄ (M = Co²⁺ or Zn²⁺) having the spinel structure upto x = 0.4. X-Ray diffraction intensities show that the spinel solid solutions are likely to have the following cation distributions: (Co²⁺)_t[Li⁺_xCo³⁺_2?3xCo⁴⁺_2x]₀O₄ and (Zn²⁺_1?xCo²⁺_x)_t[Li⁺_xCo³⁺_2?3xCo⁴⁺_2x]₀O₄. Electrical resistivity and Seebeck coefficient data indicate that the electron transport in these systems occurs by a small-polaron hopping mechanism.     

Sn-doped Li<Subscript>1.2</Subscript>Mn<Subscript>0.54</Subscript>Ni<Subscript>0.13</Subscript>Co<Subscript>0.13</Subscript>O<Subscript>2</Subscript> cathode materials for lithium-ion batteries with enhanced electrochemical performance

Sn-doped Li-rich layered oxides of Li_1.2Mn_0.54-x Ni_0.13Co_0.13Sn _x O₂ have been synthesized via a sol-gel method, and their microstructure and electrochemical performance have been studied. The addition of Sn⁴⁺ ions has no distinct influence on the crystal structure of the materials. After doped with an appropriate amount of Sn⁴⁺, the electrochemical performance of Li_1.2Mn_0.54-x Ni_0.13Co_0.13Sn _x O₂ cathode materials is significantly enhanced. The optimal electrochemical performance is obtained at x = 0.01. The Li_1.2Mn_0.53Ni_0.13Co_0.13Sn_0.01O₂ electrode delivers a high initial discharge capacity of 268.9 mAh g^?1 with an initial coulombic efficiency of 76.5% and a reversible capacity of 199.8 mAh g^?1 at 0.1 C with capacity retention of 75.2% after 100 cycles. In addition, the Li_1.2Mn_0.53Ni_0.13Co_0.13Sn_0.01O₂ electrode exhibits the superior rate capability with discharge capacities of 239.8, 198.6, 164.4, 133.4, and 88.8 mAh g^?1 at 0.2, 0.5, 1, 2, and 5 C, respectively, which are much higher than those of Li_1.2Mn_0.54Ni_0.13Co_0.13O₂ (196.2, 153.5, 117.5, 92.7, and 43.8 mAh g^?1 at 0.2, 0.5, 1, 2, and 5 C, respectively). The substitution of Sn⁴⁺ for Mn⁴⁺ enlarges the Li⁺ diffusion channels due to its larger ionic radius compared to Mn⁴⁺ and enhances the structural stability of Li-rich oxides, leading to the improved electrochemical performance in the Sn-doped Li_1.2Mn_0.54Ni_0.13Co_0.13O₂ cathode materials.     

Color Point Tuning in Lu3−x−yMnxAl5−xSixO12:yCe3+ for White LEDs

A series of the solid‐solution phosphors Lu_3?x?yMn_xAl_5?xSi_xO₁₂:yCe³⁺ is synthesized by solid‐state reaction. The obtained phosphors possess the garnet structure and exhibit similar excitation properties as the phosphor Lu₃Al₅O₁₂:Ce³⁺, but with an effectively improved red component in the emission spectrum. This can be attributed to the energy transfer from Ce³⁺ to Mn²⁺. Our investigation reveals that electric dipole–quadrupole interactions dominate the energy‐transfer mechanism and that the critical distance determined by the spectral overlap method is about 9.21 Å. The color‐tunable emissions of the Lu_3?x?yMn_xAl_5?xSi_xO₁₂:yCe³⁺ phosphor as a function of Mn₃Al₂Si₃O₁₂ content are realized by continuously shifting the chromaticity coordinates from (0.354, 0.570) to (0.462, 0.494). They indicate that the obtained material may have potential application as a blue radiation‐converting phosphor for white LEDs with high‐quality white light.     

Electrochemically Generated γ‐LixV2O5 as Insertion Host for High‐Energy Li‐Ion Capacitors

In this study, we explored the feasibility of using electrochemically generated γ‐Li_xV₂O₅ as an insertion‐type anode in the lithium‐ion capacitor (LIC) with activated carbon (AC) as a cathode. Along with the native form of V₂O₅, their carbon composites are also used as the electrode material which is prepared by high‐energy ball milling. The electrochemical pre‐lithiation strategy is used to generate the desired γ‐phase of V₂O₅ (γ‐Li_xV₂O₅). Under the optimized mass loading conditions, the LICs are assembled with γ‐Li_xV₂O₅ as anode and AC as a cathode in the organic medium. Among the different LICs fabricated, AC/γ‐Li_xV₂O₅‐BM50 configuration delivered an energy density of 33.91 Wh kg^?1 @ 0.22 kW kg^?1 with excellent capacity retention characteristics. However, a dramatic increase in energy density (43.98 Wh kg^?1@0.28 kW kg^?1) is noted after the electrolyte modification with fluoroethylene carbonate. The high temperature performance of the assembled LIC is also studied and found that γ‐Li_xV₂O₅ phase can be used as a potential battery‐type component to construct high‐performance hybrid charge storage devices.     

P2‐Na0.67AlxMn1−xO2: Cost‐Effective,Stable and High‐Rate Sodium Electrodes by Suppressing Phase Transitions and Enhancing Sodium Cation Mobility

Sodium layered P2‐stacking Na_0.67MnO₂ materials have shown great promise for sodium‐ion batteries. However, the undesired Jahn–Teller effect of the Mn⁴⁺/Mn³⁺ redox couple and multiple biphasic structural transitions during charge/discharge of the materials lead to anisotropic structure expansion and rapid capacity decay. Herein, by introducing abundant Al into the transition‐metal layers to decrease the number of Mn³⁺, we obtain the low cost pure P2‐type Na_0.67Al_xMn_1?xO₂ (x=0.05, 0.1 and 0.2) materials with high structural stability and promising performance. The Al‐doping effect on the long/short range structural evolutions and electrochemical performances is further investigated by combining in situ synchrotron XRD and solid‐state NMR techniques. Our results reveal that Al‐doping alleviates the phase transformations thus giving rise to better cycling life, and leads to a larger spacing of Na⁺ layer thus producing a remarkable rate capability of 96 mAh g^‐1 at 1200 mA g^‐1.     

P2‐Na0.67AlxMn1−xO2: Cost‐Effective,Stable and High‐Rate Sodium Electrodes by Suppressing Phase Transitions and Enhancing Sodium Cation Mobility

Sodium layered P2‐stacking Na_0.67MnO₂ materials have shown great promise for sodium‐ion batteries. However, the undesired Jahn–Teller effect of the Mn⁴⁺/Mn³⁺ redox couple and multiple biphasic structural transitions during charge/discharge of the materials lead to anisotropic structure expansion and rapid capacity decay. Herein, by introducing abundant Al into the transition‐metal layers to decrease the number of Mn³⁺, we obtain the low cost pure P2‐type Na_0.67Al_xMn_1?xO₂ (x=0.05, 0.1 and 0.2) materials with high structural stability and promising performance. The Al‐doping effect on the long/short range structural evolutions and electrochemical performances is further investigated by combining in situ synchrotron XRD and solid‐state NMR techniques. Our results reveal that Al‐doping alleviates the phase transformations thus giving rise to better cycling life, and leads to a larger spacing of Na⁺ layer thus producing a remarkable rate capability of 96 mAh g^‐1 at 1200 mA g^‐1.     

Synthesis of Highly Active and Stable Spinel‐Type Oxygen Evolution Electrocatalysts by a Rapid Inorganic Self‐Templating Method

Composition‐adjustable spinel‐type metal oxides, Mn_xCo_3?xO_4?δ (x=0.8–1.4), were synthesized in ethanol solutions by a rapid inorganic self‐templating mechanism using KCl nanocrystals as the structure‐directing agent. The Mn_xCo_3?xO_4?δ materials showed ultrahigh oxygen evolution activity and strong durability in alkaline solutions, and are capable of delivering a current density of 10 mA cm^?2 at 1.58 V versus the reversible hydrogen electrode in 0.1 M KOH solution, which is superior in comparison to IrO₂ catalysts under identical experimental conditions, and comparable to the most active noble‐metal and transition‐metal oxygen evolution electrocatalysts reported so far. The high performance for catalytic oxygen evolution originates from both compositional and structural features of the synthesized materials. The moderate content of Mn doping into the spinel framework led to their improved electronic conductivity and strong oxidizing ability, and the well‐developed porosity, accompanied with the high affinity between OH^? reactants and catalyst surface, contributed to the smooth mass transport, thus endowing them with superior oxygen evolution activity.     

Mn−O Covalency Governs the Intrinsic Activity of Co‐Mn Spinel Oxides for Boosted Peroxymonosulfate Activation

Transition metal (TM)‐based bimetallic spinel oxides can efficiently activate peroxymonosulfate (PMS) presumably attributed to enhanced electron transfer between TMs, but the existing model cannot fully explain the efficient TM redox cycling. Here, we discover a critical role of TM?O covalency in governing the intrinsic catalytic activity of Co_3?xMn_xO₄ spinel oxides. Experimental and theoretical analysis reveals that the Co sites significantly raises the Mn valence and enlarges Mn?O covalency in octahedral configuration, thereby lowering the charge transfer energy to favor Mn_Oh–PMS interaction. With appropriate Mn^IV/Mn^III ratio to balance PMS adsorption and Mn^IV reduction, the Co_1.1Mn_1.9O₄ exhibits remarkable catalytic activities for PMS activation and pollutant degradation, outperforming all the reported TM spinel oxides. The improved understandings on the origins of spinel oxides activity for PMS activation may inspire the development of more active and robust metal oxide catalysts.     

Self‐Template Synthesis of Hybrid Porous Co3O4–CeO2 Hollow Polyhedrons for High‐Performance Supercapacitors

In this work, hybrid porous Co₃O₄–CeO₂ hollow polyhedrons have been successfully obtained via a simple cation‐exchange route followed by heat treatment. In the synthesis process, ZIF‐67 polyhedron frameworks are firstly prepared, which not only serve as a host for the exchanged Ce3⁺ ions but also act as the template for the synthesis of hybrid porous Co₃O₄–CeO₂ hollow polyhedrons. When utilized as electrode materials for supercapacitors, the hybrid porous Co₃O₄–CeO₂ hollow polyhedrons delivered a large specific capacitance of 1288.3 F g^?1 at 2.5 A g^?1 and a remarkable long lifespan cycling stability (<3.3 % loss after 6000 cycles). Furthermore, an asymmetric supercapacitor (ASC) device based on hybrid porous Co₃O₄–CeO₂ hollow polyhedrons was assembled. The ASC device possesses an energy density of 54.9 W h kg^?1, which can be retained to 44.2 W h kg^?1 even at a power density of 5100 W kg^?1, indicating its promising application in electrochemical energy storage. More importantly, we believe that the present route is a simple and versatile strategy for the preparation of other hybrid metal oxides with desired structures, chemical compositions and applications.     

Kinetics and Mechanism of Oxidation of S2O32− by a Co‐Bound μ‐Amido‐μ‐Superoxo Complex

In acetate buffer media (pH 4.5–5.4) thiosulfate ion (S₂O₃^2?) reduces the bridged superoxo complex, [(NH₃)₄Co^III(μ‐NH₂,μ‐O₂)Co^III(NH₃)₄]⁴⁺ ( 1 ) to its corresponding μ‐peroxo product, [(NH₃)₄Co^III(μ‐NH₂,μ‐O₂)Co^III(NH₃)₄]³⁺ ( 2 ) and along a parallel reaction path, simultaneously S₂O₃^2? reacts with 1 to produce the substituted μ‐thiosulfato‐μ‐superoxo complex, [(NH₃)₄Co^III(μ‐S₂O₃,μ‐O₂)Co^III(NH₃)₄]³⁺ ( 3 ). The formation of μ‐thiosulfato‐μ‐superoxo complex ( 3 ) appears as a precipitate which on being subjected to FTIR shows absorption peaks that support the presence of Co(III)‐bound S‐coordinated S₂O₃^2? group. In reaction media, 3 readily dissolves to further react with S₂O₃^2? to produce μ‐thiosulfato‐μ‐peroxo product, [(NH₃)₄Co^III(μ‐S₂O₃,μ‐O₂)Co^III(NH₃)₄]²⁺ ( 4 ). The observed rate (k₀) increases with an increase in [T_Thio] ([T_Thio] is the analytical concentration of S₂O₃^2?) and temperature (T), but it decreases with an increase in [H⁺] and the ionic strength (I). Analysis of the log A_t versus time data (A is the absorbance of 1 at time t) reveals that overall the reaction follows a biphasic consecutive reaction path with rate constants k₁ and k₂ and the change of absorbance is equal to {a₁ exp(–k₁t) + a₂ exp(–k₂t)}, where k₁ > k₂.     

catena‐Poly­[[di­aqua­lithium(I)]‐μ‐[9H‐purine‐2,6(1H,3H)‐dionato‐O2:N7]]

In the title compound, [Li(C₅H₃N₄O₂)(H₂O)₂]_n, the coordinate geometry about the Li⁺ ion is distorted tetrahedral and the Li⁺ ion is bonded to N and O atoms of adjacent ligand mol­ecules forming an infinite polymeric chain with Li—O and Li—N bond lengths of 1.901 (5) and 2.043 (6) Å, respectively. Tetrahedral coordination at the Li⁺ ion is completed by two cis water mol­ecules [Li—O 1.985 (6) and 1.946 (6) Å]. The crystal structure is stabilized both by the polymeric structure and by a hydrogen‐bond network involving N—H?O, O—H?O and O—H?N hydrogen bonds.     

Molybdenum Substitution for Improving the Charge Compensation and Activity of Li2MnO3

Lithium‐rich layer‐structured oxides xLi₂MnO₃? (1?x)LiMO₂ (0<x<1, M=Mn, Ni, Co, etc.) are interesting and potential cathode materials for high energy‐density lithium ion batteries. However, the characteristic charge compensation contributed by O^2? in Li₂MnO₃ leads to the evolution of oxygen during the initial Li⁺ ion extraction at high voltage and voltage fading in subsequent cycling, resulting in a safety hazard and poor cycling performance of the battery. Molybdenum substitution was performed in this work to provide another electron donor and to enhance the electrochemical activity of Li₂MnO₃‐based cathode materials. X‐ray diffraction and adsorption studies indicated that Mo⁵⁺ substitution expands the unit cell in the crystal lattice and weakens the Li?O and Mn?O bonds, as well as enhancing the activity of Li₂MnO₃ by lowering its delithiation potential and suppressing the release of oxygen. In addition, the chemical environment of O^2? ions in molybdenum‐substituted Li₂MnO₃ is more reversible than in the unsubstituted sample during cycling. Therefore molybdenum substitution is expected to improve the performances of the Li₂MnO₃‐based lithium‐rich cathode materials.     

Sol-gel Synthesis and Electrochemical Performance of Li4-xMgxTi5-xZrxO12 Anode Material for Lithium-ion Batteries

The anode materials Li_4?xMg_xTi_5?xZr_xO₁₂ (x=0, 0.05, 0.1) were successfully synthesized by sol‐gel method using Ti(OC₄H₉)₄, CH₃COOLi·2H₂O, MgCl₂·6H₂O and Zr(NO₃)₃·6H₂O as raw materials. The crystalline structure, morphology and electrochemical properties of the as‐prepared materials were characterized by XRD, SEM, cyclic voltammograms (CV), electrochemical impedance spectroscopy (EIS) and charge‐discharge cycling tests. The results show that the lattice parameters of the Mg‐Zr doped samples are slightly larger than that of the pure Li₄Ti₅O₁₂, and Mg‐Zr doping does not change the basic Li₄Ti₅O₁₂ structure. The rate capability of Li_4?xMg_xTi_5?xZr_xO₁₂ (x=0.05, 0.1) electrodes is significantly improved due to the expansile Li⁺ diffusion channel and reduced charge transfer resistance. In this study, Li_3.95Mg_0.05Ti_4.95Zr_0.05O₁₂ represented a relatively good rate capability and cycling stability, after 400 cycles at 10 C, the discharge capacity retained as 134.74 mAh·g^?1 with capacity retention close to 100%. The excellent rate capability and good cycling performance make Li_3.95Mg_0.05Ti_4.95Zr_0.05O₁₂ a promising anode material in lithium‐ion batteries.     

Hydrogen Production by Water Dissociation in Surface‐Modified BaCoxFeyZr1−x−yO3−δ Hollow‐Fiber Membrane Reactor with Improved Oxygen Permeation

A porous perovskite BaCo_xFe_yZr_0.9?x?yPd_0.1O_3?δ (BCFZ‐Pd) coating was deposited onto the outer surface of a BaCo_xFe_yZr_1?x?yO_3?δ (BCFZ) perovskite hollow‐fiber membrane. The surface morphology of the modified BCFZ fiber was characterized by scanning electron microscopy (SEM), indicating the formation of a BCFZ‐Pd porous layer on the outer surface of a dense BCFZ hollow‐fiber membrane. The oxygen permeation flux of the BCFZ membrane with a BCFZ‐Pd porous layer increased 3.5 times more than that of the blank BCFZ membrane when feeding reactive CH₄ onto the permeation side of the membrane. The blank BCFZ membrane and surface‐modified BCFZ membrane were used as reactors to shift the equilibrium of thermal water dissociation for hydrogen production because they allow the selective removal of the produced oxygen from the water dissociation system. It was found that the hydrogen production rate increased from 0.7 to 2.1 mL H₂ min^?1 cm^?2 at 950 °C after depositing a BCFZ‐Pd porous layer onto the BCFZ membrane.     

Origin of the irreversible plateau (4.5 V) of Li[Li0.182Ni0.182Co0.091Mn0.545]O2 layered material

Layered LiNi_0.4Co_0.2Mn_0.4O₂, Li[Li_0.182Ni_0.182Co_0.091Mn_0.545]O₂, Li[Li_1/3Mn_2/3]O₂ powder materials were prepared by rheological phase method. XRD characterization shows that these samples all have analogous structure to LiCoO₂. Li[Li_0.182Ni_0.182Co_0.091Mn_0.545]O₂ can be considered to be the solid solution of LiNi_0.4Co_0.2Mn_0.4O₂ and Li[Li_1/3Mn_2/3]O₂. Detailed information from XRD, ex situ XPS measurement and electrochemical analysis of these three materials reveals the origin of the irreversible plateau (4.5 V) of Li[Li_0.182Ni_0.182Co_0.091Mn_0.545]O₂ electrode. The irreversible oxidation reaction occurred in the first charging above 4.5 V is ascribed to the contribution of Li[Li_1/3Mn_2/3]O₂ component, which maybe extract Li⁺ from the transition layer in Li[Li_1/3Mn_2/3]O₂ or Li[Li_0.182Ni_0.182Co_0.091Mn_0.545]O₂ through oxygen release. This step also activates Mn⁴⁺ of Li[Li_1/3Mn_2/3]O₂ or Li[Li_0.182Ni_0.182Co_0.091Mn_0.545]O₂, it can be reversibly reduced/oxidized between Mn⁴⁺ and Mn³⁺ in the subsequent cycles.     

Insulator–metal transition in Nd0.8Na0.2Mn(1−x)CoxO3 perovskites

The electric and magnetic properties of the perovskites Nd_0.8Na_0.2Mn_(1−x)Co_xO₃ (0x0.2) prepared by the usual ceramic procedure were investigated. The insulator-to-metal-like (IM) transition, closely related to a ferromagnetic arrangement, was revealed for the composition of x=0.04 and a similar tendency was detected for x=0. The insulating behavior persists down to low temperatures for higher contents of cobalt ions in spite of the transition to the bulk ferromagnetism. The properties are interpreted in terms of the steric distortion, tilting of the Mn(Co)O₆ octahedra and the double-exchange interactions of the type Mn³⁺–O²⁻–Mn⁴⁺and Mn^3.5+δ–O²⁻–Co²⁺, respectively. Presence of antiferromagnetic domains in the ferromagnetic matrix for the most of cobalt-substituted samples is supposed.     

The Neat Ternary Solid K5−xCo1−xSn9 with Endohedral [Co@Sn9]5− Cluster Units: A Precursor for Soluble Intermetalloid [Co2@Sn17]5− Clusters

A new type of Zintl phase is presented that contains endohedrally filled clusters and that allows for the formation of intermetalloid clusters in solution by a one‐step synthesis. The intermetallic compound K_5?xCo_1?xSn₉ was obtained by the reaction of a preformed Co? Sn alloy with potassium and tin at high temperatures. The diamagnetic saltlike ternary phase contains discrete [Co@Sn₉]^5? clusters that are separated by K⁺ ions. The intermetallic compound K_5?xCo_1?xSn₉ readily and incongruently dissolves in ethylenediamine and in the presence of 4,7,13,16,21,24‐hexaoxa‐1,10‐diazabicyclo[8.8.8]hexacosane (2.2.2‐crypt), thereby leading to the formation of crystalline [K([2.2.2]crypt)]₅[Co₂Sn₁₇]. The novel polyanion [Co₂Sn₁₇]^5? contains two Co‐filled Sn₉ clusters that share one vertex. Both compounds were characterized by single‐crystal X‐ray structure analysis. The diamagnetism of K_5?xCo_1?xSn₉ and the paramagnetism of [K([2.2.2]crypt)]₅[Co₂Sn₁₇] have been confirmed by superconducting quantum interference device (SQUID) and EPR measurements, respectively. Quantum chemical calculations reveal an endohedral Co^1? atom in an [Sn₉]^4? nido cluster for [Co@Sn₉]^5? and confirm the stability of the paramagnetic [Co₂Sn₁₇]^5? unit.     

Li3PO4‐Coated LiNi0.5Mn1.5O4: A Stable High‐Voltage Cathode Material for Lithium‐Ion Batteries

LiNi_0.5Mn_1.5O₄ is regarded as a promising cathode material to increase the energy density of lithium‐ion batteries due to the high discharge voltage (ca. 4.7 V). However, the interface between the LiNi_0.5Mn_1.5O₄ cathode and the electrolyte is a great concern because of the decomposition of the electrolyte on the cathode surface at high operational potentials. To build a stable and functional protecting layer of Li₃PO₄ on LiNi_0.5Mn_1.5O₄ to avoid direct contact between the active materials and the electrolyte is the emphasis of this study. Li₃PO₄‐coated LiNi_0.5Mn_1.5O₄ is prepared by a solid‐state reaction and noncoated LiNi_0.5Mn_1.5O₄ is prepared by the same method as a control. The materials are fully characterized by XRD, FT‐IR, and high‐resolution TEM. TEM shows that the Li₃PO₄ layer (<6 nm) is successfully coated on the LiNi_0.5Mn_1.5O₄ primary particles. XRD and FT‐IR reveal that the synthesized Li₃PO₄‐coated LiNi_0.5Mn_1.5O₄ has a cubic spinel structure with a space group of Fd$\bar 3$ m, whereas noncoated LiNi_0.5Mn_1.5O₄ shows a cubic spinel structure with a space group of P4₃32. The electrochemical performance of the prepared materials is characterized in half and full cells. Li₃PO₄‐coated LiNi_0.5Mn_1.5O₄ shows dramatically enhanced cycling performance compared with noncoated LiNi_0.5Mn_1.5O₄.