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.     

Pyroxene‐type compounds NaM3+Ge2O6, with M = Ga,Mn, Sc and In

The four title compounds, namely sodium gallium germanate, NaGaGe₂O₆, sodium manganese vanadate germanate, NaMnV_0.1Ge_1.9O₆, sodium scandium germanate, NaScGe₂O₆, and sodium indium germanate, NaInGe₂O₆, adopt the high‐temperature structure of the pyroxene‐type chain germanates, with monoclinic symmetry and space group C2/c. The lattice parameters, the individual and average bond lengths involving M1, and the distortion parameters scale well with the ionic radius of the M1 cation. NaGaGe₂O₆ has more distorted M1 sites and more extended tetrahedral chains than NaInGe₂O₆, in which a high degree of kinking is required to maintain the connection between the octahedral and tetrahedral building units of the pyroxene structure. An exceptional case is NaMnGe₂O₆, in which the strong Jahn–Teller effect of Mn³⁺ results in more distorted octahedral sites than expected according to linear extrapolation from the other NaM³⁺Ge₂O₆ pyroxenes. In contrast with the literature, minor incorporations of V⁵⁺ in the tetrahedral site and a corresponding reduction of Mn³⁺ to Mn²⁺ in the octahedral sites in the present sample lower the Jahn–Teller distortion and stabilize the Mn‐bearing pyroxene, even allowing its synthesis at ambient pressure.     

Sodium and Manganese Stoichiometry of P2‐Type Na2/3MnO2

To realize a reversible solid‐state Mn^III/IV redox couple in layered oxides, co‐operative Jahn–Teller distortion (CJTD) of six‐coordinate Mn^III (t_2g³–e_g¹) is a key factor in terms of structural and physical properties. We develop a single‐phase synthesis route for two polymorphs, namely distorted and undistorted P2‐type Na_2/3MnO₂ having different Mn stoichiometry, and investigate how the structural and stoichiometric difference influences electrochemical reaction. The distorted Na_2/3MnO₂ delivers 216 mAh g^?1 as a 3 V class positive electrode, reaching 590 Wh (kg oxide)^?1 with excellent cycle stability in a non‐aqueous Na cell and demonstrates better electrochemical behavior compared to undistorted Na_2/3MnO₂. Furthermore, reversible phase transitions correlated with CJTD are found upon (de)sodiation for distorted Na_2/3MnO₂, providing a new insight into utilization of the Mn^III/IV redox couple for positive electrodes of Na‐ion batteries.     

Electrochemical and Structural Study of Layered P2‐Type Na2/3Ni1/3Mn2/3O2 as Cathode Material for Sodium‐Ion Battery

P2‐type Na_2/3Ni_1/3Mn_2/3O₂ was synthesized by a controlled co‐precipitation method followed by a high‐temperature solid‐state reaction and was used as a cathode material for a sodium‐ion battery (SIB). The electrochemical behavior of this layered material was studied and an initial discharge capacity of 151.8 mA h g^?1 was achieved in the voltage range of 1.5–3.75 V versus Na⁺/Na. The retained discharge capacity was found to be 123.5 mA h g^?1 after charging/discharging 50 cycles, approximately 81.4 % of the initial discharge capacity. In situ X‐ray diffraction analysis was used to investigate the sodium insertion and extraction mechanism and clearly revealed the reversible structural changes of the P2‐Na_2/3Ni_1/3Mn_2/3O₂ and no emergence of the O2‐Ni_1/3Mn_2/3O₂ phase during the cycling test, which is important for designing stable and high‐performance SIB cathode materials.     

Crystal structures of disordered A2Mn3+M5+O6 (A=Sr,Ca; M=Sb,Nb, Ru) perovskites

Polycrystalline samples of A₂MnMO₆ (A=Sr, Ca; M=Nb, Sb, Ru) were prepared by conventional solid state synthesis and their crystal structures were determined using neutron powder diffraction data. All six compounds can be classified as distorted, disordered perovskites. The Mn³⁺/M⁵⁺ distribution is disordered in all six compounds. The strontium containing compounds, Sr₂MnMO₆ (M=Nb, Sb, Ru), undergo out of phase rotations of the octahedra about the c-axis (tilt system a⁰a⁰c⁻) leading to tetragonal I4/mcm space group symmetry. The calcium containing compounds, Ca₂MnMO₆ (M=Nb, Ru, Sb), have orthorhombic Pnma space group symmetry, as a result of a GdFeO₃-type octahedral tilting distortion (tilt system a⁻b⁺a⁻). A cooperative Jahn–Teller distortion is observed in Sr₂MnSbO₆ and Sr₂MnRuO₆, but it is much smaller than the distortion observed in LnMnO₃ (Ln=lanthanide ion) perovskites. It is possible that Jahn–Teller distortions of the MnO₆ octahedra take place on a short-range length scale in the other four compounds, but there is little or no evidence for cooperative ordering of the local distortions. These findings demonstrate a link between orbital ordering, cation ordering and octahedral tilting.     

Electrochemical intercalation and deintercalation of NaxMnO2 bronzes

Various Na_xMnO₂ bronzes have been electrochemically deintercalated. Na_0.40MnO₂ has a channel structure which is maintained for a large intercalation range (0.30 ≤ × ≤ 0.58). In order to explain the upper intercalation limit, an ordered sodium distribution between two types of Na⁺ sites is proposed. Na_0.70MnO₂ and α-NaMnO₂ have lamellar structures of P2 and 0′3 types. During intercalation the original P2 type is maintained for 0.45 ≤ × ≤ 0.85 while two reversible structural transitions are observed from α-NaMnO₂. A similar behavior occurs during the deintercalation of the high-temperature β-NaMnO₂ variety. In each case of the structural transition the double octahedral layers remain unchanged. Electronic localization (increased by Mn³⁺ Jahn—Teller effect) tends to trap the Na⁺ ions and therefore increases the relaxation time of the investigated materials.     

Realizing Complete Solid-Solution Reaction in High Sodium Content P2-Type Cathode for High-Performance Sodium-Ion Batteries

P2-type layered oxides suffer from an ordered Na⁺/vacancy arrangement and P2→O2/OP4 phase transitions, leading them to exhibit multiple voltage plateaus upon Na⁺ extraction/insertion. The deficient sodium in the P2-type cathode easily induces the bad structural stability at deep desodiation states and limited reversible capacity during Na⁺ de/insertion. These drawbacks cause poor rate capability and fast capacity decay in most P2-type layered oxides. To address these challenges, a novel high sodium content (0.85) and plateau-free P2-type cathode-Na_0.85Li_0.12Ni_0.22Mn_0.66O₂ (P2-NLNMO) was developed. The complete solid-solution reaction over a wide voltage range ensures both fast Na⁺ mobility (10⁻¹¹ to 10⁻¹⁰ cm² s⁻¹) and small volume variation (1.7 %). The high sodium content P2-NLNMO exhibits a higher reversible capacity of 123.4 mA h g⁻¹, superior rate capability of 79.3 mA h g⁻¹ at 20 C, and 85.4 % capacity retention after 500 cycles at 5 C. The sufficient Na and complete solid-solution reaction are critical to realizing high-performance P2-type cathodes for sodium-ion batteries.     

The Distorted Structure of [Au(GeCl3)3]2–

It is well known that [Au(PR₃)₃]⁺ compounds (R any organic ligand) adopt a trigonal planar AuP₃ arrangement, small distortions being only due to steric repulsion between the ligands R. This is supported by relativistic MP2 geometry optimizations for the free gas phase species which yield the ideal trigonal planar AuP₃ structure for the model compound [Au(PH₃)₃]⁺. Model calculations on the recently synthesized compound [Au(GeCl₃)₃]^2– which is isoelectronic to [Au(PR₃)₃]⁺ also reveal a trigonal planar AuGe₃ structure. However, the recently determined X‐ray structure of [Au₂(dppm)₂][Au(GeCl₃)₃] shows a T‐shaped AuGe₃ arrangement. We demonstrate that this distortion is caused by solid state effects, that is the influence of the counter cations are necessary in order to obtain the observed symmetry breaking. However, unlike AuF₃ which has recently been determined by electron diffraction to be T‐shaped in the gas phase caused by a first‐order Jahn‐Teller effect, this distortion cannot be so easily rationalized by a similar AuGe₃ Jahn‐Teller effect along the e′ distortion mode. Model calculations on Na₂[Au(GeCl₃)₃] show that the strong Coulomb interaction between the negatively charged chlorine atoms and the Na⁺ ions leads to a distortion from a trigonal planar to the T‐shaped AuGe₃ arrangement lowering the energy by 137 kJ mol^–1.     

(Li0.91Mn0.09)Mn2O4

Lithium manganese oxide crystals with composition (Li_0.91Mn_0.09)Mn₂O₄ were synthesized by a flux method. The crystals have a structure closely related to that of the cubic spinel LiMn₂O₄, but 9% of the lithium ions in the tetrahedral 4a site are substituted by Mn²⁺ ions. This substitution lowers the average Mn oxidation state below 3.5+, resulting in a Jahn–Teller distortion of the MnO₆ octahedron.     

长循环高电压钠离子电池正极材料P2-Na2/3Mn1/3Bi1/3Ni1/3O2的合成及性能

镍基层状氧化物NaNiO₂钠离子电池材料具有高电压和高容量的特性,且制备方法较为简单,但姜-泰勒(Jahn-Teller)效应使其在高倍率循环下容量较低以及在高电压(4.5 V)下无法稳定循环。通过调节溶胶-凝胶工艺的条件,设计、合成了Na_2/3Mn_1/3Bi_1/3Ni_1/3O₂片层状金属氧化物,并将其作为正极活性材料,在空气环境中组装成钠离子电池,进行电化学测试,考察Bi、Mn掺入量对电池电化学影响。研究结果表明：当金属Mn和Bi共掺时,在1.2~4.5 V宽电压范围内,电池在循环50周后容量为90.39 mAh·g^-1。在2.0~4.0 V电压范围内1.0C (115 mA·g^-1)倍率下恒流充放电50周后的容量保持率为96.96%,循环850周后的保持率为80.15%,具有良好的循环稳定性和安全性。     

长循环高电压钠离子电池正极材料P2-Na2/3Mn1/3Bi1/3Ni1/3O2的合成及性能

镍基层状氧化物NaNiO₂钠离子电池材料具有高电压和高容量的特性,且制备方法较为简单,但姜-泰勒(Jahn-Teller)效应使其在高倍率循环下容量较低以及在高电压(4.5 V)下无法稳定循环。通过调节溶胶-凝胶工艺的条件,设计、合成了Na_2/3Mn_1/3Bi_1/3Ni_1/3O₂片层状金属氧化物,并将其作为正极活性材料,在空气环境中组装成钠离子电池,进行电化学测试,考察Bi、Mn掺入量对电池电化学影响。研究结果表明：当金属Mn和Bi共掺时,在1.2~4.5 V宽电压范围内,电池在循环50周后容量为90.39 mAh·g^-1。在2.0~4.0 V电压范围内1.0C (115 mA·g^-1)倍率下恒流充放电50周后的容量保持率为96.96%,循环850周后的保持率为80.15%,具有良好的循环稳定性和安全性。     

长循环高电压钠离子电池正极材料P2-Na2/3Mn1/3Bi1/3Ni1/3O2的合成及性能

镍基层状氧化物NaNiO₂钠离子电池材料具有高电压和高容量的特性,且制备方法较为简单,但姜-泰勒(Jahn-Teller)效应使其在高倍率循环下容量较低以及在高电压(4.5 V)下无法稳定循环。通过调节溶胶-凝胶工艺的条件,设计、合成了Na_2/3Mn_1/3Bi_1/3Ni_1/3O₂片层状金属氧化物,并将其作为正极活性材料,在空气环境中组装成钠离子电池,进行电化学测试,考察Bi、Mn掺入量对电池电化学影响。研究结果表明:当金属Mn和Bi共掺时,在1.2~4.5 V宽电压范围内,电池在循环50周后容量为90.39 mAh·g^-1。在2.0~4.0 V电压范围内1.0C (115 mA·g^-1)倍率下恒流充放电50周后的容量保持率为96.96%,循环850周后的保持率为80.15%,具有良好的循环稳定性和安全性。     

Über das System Ba2Zn1−xCuxUO6 — ein schwingungsspektroskopischer Nachweis des Jahn-Teller-Effekts

On the System Ba₂Zn_1?xCu_xUO₆. A Vibrational Spectroscopic Proof of the Jahn Teller Effect The ordered perovskites Ba₂ZnUO₆ (cubic, space group Fm3m) and Ba₂CuUO₆ (tetragonal, space group I₄/mmm) form solid solutions. For small Cu content the lattice symmetry is cubic, with x ≥ 0.25 an increasing tetragonal distortion (c/a √2 > 1) is observed. From the vibrational spectra and in accordance with the factor group analysis the symmetry of the UO₆ octahedra is for small Cu content O_h and on the Cu-rich side D_4h. In the region of the lattice vibrations (T₂ field) the lifting of the degeneracy — due to the Jahn Teller effect of Cu²⁺ — leads to a band separation, which decreases with sinking copper content. Therefore the Jahn Teller effect is easily noticeable with vibrational spectroscopic methods. In the corresponding series with W^VI the vibrational spectroscopic investigations lead qualitatively to the same results as in the U^VI system. As further examples the stacking polytypes Ba₂ZnTeO₆ and Ba₂CuTeO₆ are considered. The vibrational spectra show, that the Jahn Teller effect in this lattice, which is strengthened by partial face-sharing of octahedra, is less pronounced than in the perovskites in which only corner-sharing is present.     

Mitigation of Jahn–Teller distortion and Na+/vacancy ordering in a distorted manganese oxide cathode material by Li substitution

Layered manganese-based oxides are promising candidates as cathode materials for sodium-ion batteries (SIBs) due to their low cost and high specific capacity. However, the Jahn–Teller distortion from high-spin Mn³⁺ induces detrimental lattice strain and severe structural degradation during sodiation and desodiation. Herein, lithium is introduced to partially substitute manganese ions to form distorted P′2-Na_0.67Li_0.05Mn_0.95O₂, which leads to restrained anisotropic change of Mn–O bond lengths and reinforced bond strength in the [MnO₆] octahedra by mitigation of Jahn–Teller distortion and contraction of MnO₂ layers. This ensures the structural stability during charge and discharge of P′2-Na_0.67Li_0.05Mn_0.95O₂ and Na⁺/vacancy disordering for facile Na⁺ diffusion in the Na layers with a low activation energy barrier of ∼0.53 eV. It exhibits a high specific capacity of 192.2 mA h g⁻¹, good cycling stability (90.3% capacity retention after 100 cycles) and superior rate capability (118.5 mA h g⁻¹ at 1.0 A g⁻¹), as well as smooth charge/discharge profiles. This strategy is effective to tune the crystal structure of layered oxide cathodes for SIBs with high performance.

Li-Substitution in P′2-Na_0.67MnO₂ mitigates the anisotropic change of Mn–O bonds and Na/vacancy ordering, and hence significantly promotes its cycling stability and rate capability as a cathode material for sodium-ion batteries.     

Effects of complexants on [Ni1/3Co1/3Mn1/3]CO3 morphology and electrochemical performance of LiNi1/3Co1/3Mn1/3O2

LiNi_1/3Co_1/3Mn_1/3O₂ cathode materials for the application of lithium ion batteries were synthesized by carbonate co-precipitation routine using different ammonium salt as a complexant. The structures and morphologies of the precursor [Ni_1/3Co_1/3Mn_1/3]CO₃ and LiNi_1/3Co_1/3Mn_1/3O₂ were investigated through X-ray diffraction, scanning electron microscope, and transmission electron microscopy. The electrochemical properties of LiNi_1/3Co_1/3Mn_1/3O₂ were examined using charge/discharge cycling and cyclic voltammogram tests. The results revealed that the microscopic structures, particle size distribution, and the morphology properties of the precursor and electrochemical performance of LiNi_1/3Co_1/3Mn_1/3O₂ were primarily dependent on the complexant. Among all as-prepared LiNi_1/3Co_1/3Mn_1/3O₂ cathode materials, the sample prepared from Na₂CO₃–NH₄HCO₃ routine using NH₄HCO₃ as the complexant showed the smallest irreversible capacity of 19.5 mAh g⁻¹ and highest discharge capacity of 178.4 mAh g⁻¹ at the first cycle as well as stable cycling performance (98.7% of the initial capacity was retained after 50 cycles) at 0.1 C (20 mA g⁻¹) in the voltage range of 2.5–4.4 V vs. Li⁺/Li. Moreover, it delivered high discharge capacity of over 135 mAh g⁻¹ at 5 C (1,000 mA g⁻¹).     

Jahn—Teller effects in substituted benzene cations. III. Gas phase emission spectrum of sym-C6Cl3H+3

The gas phase emission spectrum of 1, 3, 5-C₆Cl₃H⁺₃ was obtained in a discharge tube. Vibronic analysis involving correlation of ion fundamental frequencies with those of parent molecules enables a detailed comparison to be made between the vibrational structure of the spectrum of the trichloro-ion and that of 1, 3, 5-C₆F₃H⁺₃. Analogous Jahn—Teller effects are shown to take place in the ground state of the two ions. The same linear coupling model is used and two possible solutions for D₆ and ω₆ are obtained by fitting the first two intervals in the 6^0,0_{v$\text{1}\text{2}$} progression in 1, 3, 5-C₆Cl ₃H⁺₃: (i) D₆ = 0.05 - 0.08, ω₆ = 455 - 447 cm^?1, (ii) D₆ = 0.39 - 0.49, ω₆ = 399 - 392 cm^?1. Arguments based on previously established criteria, and applied here to the case of the 1, 3, 5-C₆Cl₃H⁺₃ ion are given to select set (ii) as being far more satisfactory in interpreting the experimental data. Fitting to a larger number of bands gave D₆ = 0.45, ω₆ = 395 cm^?1. The Jahn—Teller potential energy barrier E^JT₆ = 178 cm^?1 is about three times greater than in the 1, 3, 5-trifluorobenzene ions, but sufficiently small for the dynamic Jahn—Teller effect to be operative in 1, 3, 5-C₆Cl₃H⁺₃. Some remarks are made concerning assignments in the excitation spectrum and matrix fluorescence analyses.     

Realizing Complete Solid‐Solution Reaction in High Sodium Content P2‐Type Cathode for High‐Performance Sodium‐Ion Batteries

P2‐type layered oxides suffer from an ordered Na⁺/vacancy arrangement and P2→O2/OP4 phase transitions, leading them to exhibit multiple voltage plateaus upon Na⁺ extraction/insertion. The deficient sodium in the P2‐type cathode easily induces the bad structural stability at deep desodiation states and limited reversible capacity during Na⁺ de/insertion. These drawbacks cause poor rate capability and fast capacity decay in most P2‐type layered oxides. To address these challenges, a novel high sodium content (0.85) and plateau‐free P2‐type cathode‐Na_0.85Li_0.12Ni_0.22Mn_0.66O₂ (P2‐NLNMO) was developed. The complete solid‐solution reaction over a wide voltage range ensures both fast Na⁺ mobility (10^?11 to 10^?10 cm² s^?1) and small volume variation (1.7 %). The high sodium content P2‐NLNMO exhibits a higher reversible capacity of 123.4 mA h g^?1, superior rate capability of 79.3 mA h g^?1 at 20 C, and 85.4 % capacity retention after 500 cycles at 5 C. The sufficient Na and complete solid‐solution reaction are critical to realizing high‐performance P2‐type cathodes for sodium‐ion batteries.     

球磨辅助高温固相法制备Li1.0Na0.2Ni0.13Co0.13Mn0.54O2正极材料及其性能

以乙酸盐(乙酸锂、乙酸钠、乙酸钴、乙酸镍、乙酸锰等)为原材料,采用球磨辅助高温固相法制备Li_1.0Na_0.2Ni_0.13Co_0.13Mn_0.54O₂正极材料。借助XRD、SEM等表征材料的结构和形貌,利用循环伏安、恒流充放电、交流阻抗等方法研究材料的电化学性能。结果表明,钠的掺杂导致颗粒表面光滑度降低,形成Na_0.77MnO_2.05新相。0.05C活化过程中,掺钠样品和未掺钠样品首次放电比容量分别为258.4 mAh·g^-1和215.8 mAh·g^-1,库伦效率分别为75.2%和72.8%;2C放电比容量分别为116.3 mAh·g^-1和106.2 mAh·g^-1。研究发现,掺钠可减小首次充放电过程的不可逆容量,提高容量保持率;改善倍率性能与容量恢复特性;降低SEI膜阻抗和电荷转移阻抗;掺钠后样品首次循环就可以基本完成Li₂MnO₃组分向稳定结构的转化,而未掺杂的样品需要两次循环才能逐步完成该过程;XPS结果表明,掺钠样品中Ni²⁺、Co³⁺、Mn⁴⁺所占比例明显提高,改善了样品的稳定性和电化学性能;循环200次后的XRD结果表明掺钠与未掺钠材料在脱嵌锂反应中的相变化过程基本一致,良好有序的层状结构遭到破坏是循环过程中容量衰减的主要原因。     

Significant improved electrochemical performance of Li(Ni1/3Co1/3Mn1/3)O2 cathode on volumetric energy density and cycling stability at high rate

Li(Ni_1/3Co_1/3Mn_1/3)O₂ microspheres with a tap density of 2.41 g cm⁻³ have been synthesized for applications in high power and high energy systems, using a simple rheological phase reaction route. Cyclic voltammograms (CV) showed no shift of anodic and cathodic peaks centred at 3.81, 3.69 V for the Ni²⁺/Ni⁴⁺ couple after first cycle. The results of power pulse area specific impedance (ASI) and differential scanning calorimetry (DSC) tests showed lower power impedance and increased thermal stability of the electrode at high rate. These merits mentioned above provided significant improved capacity and rate performance for Li(Ni_1/3Co_1/3Mn_1/3)O₂ microspheres, which 159, 147 mAh g⁻¹ discharge capacity was delivered after 100 cycles between 2.5–4.6 V vs. Li at a different discharge rate of 2.5 C (500 mA g⁻¹), 5 C and a constant 0.5 C charge rate, respectively.