Atomic Structure and Kinetics of NASICON NaxV2(PO4)3 Cathode for Sodium‐Ion Batteries

Na₃V₂(PO₄)₃ is one of the most important cathode materials for sodium‐ion batteries, delivering about two Na extraction/insertion from/into the unit structure. To understand the mechanism of sodium storage, a detailed structure of rhombohedral Na₃V₂(PO₄)₃ and its sodium extracted phase of NaV₂(PO₄)₃ are investigated at the atomic scale using a variety of advanced techniques. It is found that two different Na sites (6b, M1 and 18e, M2) with different coordination environments co‐exist in Na₃V₂(PO₄)₃, whereas only one Na site (6b, M1) exists in NaV₂(PO₄)₃. When Na is extracted from Na₃V₂(PO₄)₃ to form NaV₂(PO₄)₃, Na⁺ occupying the M2 site (CN = 8) is extracted and the rest of the Na remains at M1 site (CN = 6). In addition, the Na atoms are not randomly distributed, possibly with an ordered arrangement in M2 sites locally for Na₃V₂(PO₄)₃. Na⁺ ions at the M1 sites in Na₃V₂(PO₄)₃ tend to remain immobilized, suggesting a direct M2‐to‐M2 conduction pathway. Only Na occupying the M2 sites can be extracted, suggesting about two Na atoms able to be extracted from the Na₃V₂(PO₄)₃ structure.     

Ultrafast Synthesis of Large-Sized and Conductive Na3V2(PO4)2F3 Simultaneously Approaches High Tap Density,Rate and Cycling Capability

The Na₃V₂(PO₄)₂F₃ (NVPF) cathode material is usually nano-sized particles exhibiting low tap density, high specific surface area, correspondingly low volume energy density, and cycle stability of the sodium-ion batteries (SIBs). Herein, a high-temperature shock (HTS) strategy is proposed to synthesize NVPF (HTS-NVPF) with uniform conducting network and high tap density. During a typical HTS process (heating rate of 1100 °C s⁻¹ for 10 s), the precursors rapidly crystallize and form large-sized and dense particles. The tight connection between particles not only enhances their contact with carbon layers, but also reduces the specific surface area that inhibits side reactions between the interfaces and the electrolyte. Besides, ultrafast synthesis of NVPF reduces the F loss and amount of Na₃V₂(PO₄)₃ impurities, which improve cycling capability. The HTS-NVPF demonstrates a high energy density of 413.4 Wh kg⁻¹ and an ultra-high specific capacity of 103.4 mAh g⁻¹ at 10 C as well as 84.2% capacity retention after 1000 cycles. In addition, the excellent temperature adaptability of HTS-NVPF (−45–55 °C) and remarkable electrochemical properties of NVPF||HC full cell demonstrate extreme competitiveness in commercial SIBs. Therefore, the HTS technique is considered to be a high-efficiency strategy to synthetize NVPF and is expected to prepare other cathode materials.     

双钨酸钇钠晶体Cr^4＋：YAG被动调Q激光特性

采用氙灯泵浦，首次实现了掺钕双钨酸钇钠（Nd:NYW）晶体以Cr^4 ：YAG作为被动调Q元件的1.064um激光运转，测量了不同小信号透过率及不同泵浦能量下激光单脉冲的输出能量、脉冲宽度和重复率，以GdCOB为倍频晶体，首次实现了Nd:NYW晶体的倍频调Q运转，测量了0.53um调Q脉冲绿光的输出能量和脉冲宽度。     

Hierarchical Engineering of Porous P2‐Na2/3Ni1/3Mn2/3O2 Nanofibers Assembled by Nanoparticles Enables Superior Sodium‐Ion Storage Cathodes

Layered transition metal oxides (TMOs) are appealing cathode candidates for sodium‐ion batteries (SIBs) by virtue of their facile 2D Na⁺ diffusion paths and high theoretical capacities but suffer from poor cycling stability. Herein, taking P2‐type Na_2/3Ni_1/3Mn_2/3O₂ as an example, it is demonstrated that the hierarchical engineering of porous nanofibers assembled by nanoparticles can effectively boost the reaction kinetics and stabilize the structure. The P2‐Na_2/3Ni_1/3Mn_2/3O₂ nanofibers exhibit exceptional rate capability (166.7 mA h g^?1 at 0.1 C with 73.4 mA h g^?1 at 20 C) and significantly improved cycle life (≈81% capacity retention after 500 cycles) as cathode materials for SIBs. The highly reversible structure evolution and Ni/Mn valence change during sodium insertion/extraction are verified by in operando X‐ray diffraction and ex situ X‐ray photoelectron spectroscopy, respectively. The facilitated electrode process kinetics are demonstrated by an additional study using the electrochemical measurements and density functional theory computations. More impressively, the prototype Na‐ion full battery built with a Na_2/3Ni_1/3Mn_2/3O₂ nanofibers cathode and hard carbon anode delivers a promising energy density of 212.5 Wh kg^?1. The concept of designing a fibrous framework composed of small nanograins offers a new and generally applicable strategy for enhancing the Na‐storage performance of layered TMO cathode materials.     

Boosting Kinetics of Ce3+/Ce4+ Redox Reaction by Constructing TiC/TiO2 Heterojunction for Cerium-Based Flow Batteries

Cerium, a unique rare earth element, possesses a relatively high abundance, low cost, and high redox voltage, making it an attractive candidate for redox flow batteries. However, the sluggish kinetics and corrosion nature of the Ce³⁺/Ce⁴⁺ electrolyte result in overpotential and degradation of carbon felt (CF) electrodes, which hinders the development of cerium-based flow batteries. Therefore, it is essential to develop an electrode with high catalytic activity and corrosion resistance to the Ce³⁺/Ce⁴⁺ electrolyte. Herein, a TiC/TiO₂ coated carbon felt (TiC/TiO₂-CF) electrode is proposed. Remarkably, the TiC/TiO₂ coating effectively minimizes the exposure of the CF to the highly corrosive cerium electrolyte, consequently enhancing the electrode's corrosion resistance. Additionally, X-ray photoelectron spectroscopy and high-resolution transmission electron microscopy characterizations reveal the formation of a heterojunction between TiC and TiO₂, which significantly enhances the redox reaction kinetics of the Ce³⁺/Ce⁴⁺ redox couple. Eventually, the practical application of TiC/TiO₂-CF catalytic electrode in a Ce–Fe flow battery is demonstrated. This study sheds light on the synthesis conditions of the TiC/TiO₂-CF electrode, elucidates its heterojunction structure, and presents a novel Ce–Fe flow battery system.     

Mn^2＋掺杂CdWO4晶体的生长及光谱特性

采用坩埚下降法技术,选用CdO∶WO3∶MnO摩尔比为100∶100∶0.5的化学组分配比,在约60℃固液界面温度梯度与0.05 mm/h生长速度条件下,成功地生长出Φ25 mm×100 mm Mn^2＋掺杂CdWO4（Mn^2＋：CWO）单晶。观测了晶体未退火、经空气和O2退火处理后的的吸收、激发和发射光谱。结果表明...     

LiFePO4 Particles Embedded in Fast Bifunctional Conductor rGO&C@Li3V2(PO4)3 Nanosheets as Cathodes for High‐Performance Li‐Ion Hybrid Capacitors

The sluggish kinetics of Faradaic reactions in bulk electrodes is a significant obstacle to achieve high energy and power density in energy storage devices. Herein, a composite of LiFePO₄ particles trapped in fast bifunctional conductor rGO&C@Li₃V₂(PO₄)₃ nanosheets is prepared through an in situ competitive redox reaction. The composite exhibits extraordinary rate capability (71 mAh g^?1 at 15 A g^?1) and remarkable cycling stability (0.03% decay per cycle over 1000 cycles at 10 A g^?1). Improved extrinsic pseudocapacitive contribution is the origin of fast kinetics, which endows this composite with high energy and power density, since the unique 2D nanosheets and embedded ultrafine LiFePO₄ nanoparticles can shorten the ion and electron diffusion length. Even applied to Li‐ion hybrid capacitors, the obtained devices still achieve high power density of 3.36 kW kg^?1 along with high energy density up to 77.8 Wh kg^?1. Density functional theory computations also validate that the remarkable rate performance is facilitated by the desirable ionic and electronic conductivity of the composite.     

Inhibition of Manganese Dissolution in Mn2O3 Cathode with Controllable Ni2+ Incorporation for High-Performance Zinc Ion Battery

Manganese-based materials are considered potential cathode materials for aqueous zinc ion batteries (ZIBs). However, the dissolution of manganese leading to an abrupt decline of capacity and the sluggish electrochemical reaction kinetics are still the main bottlenecks restricting their further development. Herein, a NiMn-layered double hydroxide-derived Ni-doped Mn₂O₃ (NM) is developed to suppress the dissolution of manganese. The incorporation of Ni²⁺ can promote electronic rearrangement and enhance the conductivity, ultimately improving the reaction kinetics and electrochemical performance of the NM. Moreover, the doped Ni²⁺ can effectively stabilize the Mn O bond of Mn₂O₃ by reducing the formation energy. In addition, the storage mechanism based on the simultaneous insertion and transformation of H⁺ and Zn²⁺ is demonstrated. Interestingly, the Ni-doped Mn₂O₃ shows a high specific capacity of 252 mAh g^–1 (0.1 A g^–1), three times more than the pure Mn₂O₃ (72 mAh g^–1). The capacity retention (≈85.6% over 2500 cycles at 1.0 A g^–1) is also more excellent when comparing with the Mn₂O₃ cathode (≈49.7%). Significantly, an ultra-high energy density of 327.6 Wh kg^–1 has been achieved using Ni-doped Mn₂O₃ cathode, which suggests that the synergistic effect of manganese and other transition metal ions provide a promising strategy for future development of ZIBs.     

A Na3V2(PO4)2O1.6F1.4 Cathode of Zn‐Ion Battery Enabled by a Water‐in‐Bisalt Electrolyte

Aqueous zinc‐ion batteries are receiving increasing attention; however, the development of high‐voltage cathodes is limited by the narrow voltage window of conventional aqueous electrolytes. Herein, it is reported that Na₃V₂(PO₄)₂O_1.6F_1.4 exhibits the excellent performance, optimal to date, among polyanion cathode materials in a novel neutral water‐in‐bisalts electrolyte of 25 m ZnCl₂ + 5 m NH₄Cl. It delivers a reversible capacity of 155 mAh g^?1 at 50 mA g^?1, a high average operating potential of ≈1.46 V, and stable cyclability of 7000 cycles at 2 A g^?1.     

Overcoming the Unfavorable Kinetics of Na3V2(PO4)2F3//SnPx Full‐Cell Sodium‐Ion Batteries for High Specific Energy and Energy Efficiency

In this work, a full‐cell sodium‐ion battery (SIB) with a high specific energy approaching 300 Wh kg^?1 is realized using a sodium vanadium fluorophosphate (Na₃V₂(PO₄)₂F₃, NVPF) cathode and a tin phosphide (SnP_x) anode, despite both electrode materials having greatly unbalanced specific capacities. The use of a cathode employing an areal loading more than eight times larger than that of the anode can be achieved by designing a nanostructured nanosized NVPF (n‐NVPF) cathode with well‐defined particle size, porosity, and conductivity. Furthermore, the high rate capability and high potential window of the full‐cell can be obtained by tuning the Sn/P ratio (4/3, 1/1, and 1/2) and the nanostructure of an SnP_x/carbon composite anode. As a result, the full‐cell SIBs employing the nanostructured n‐NVPF cathode and the SnP_x/carbon composite anode (Sn/P = 1/1) exhibit outstanding specific energy (≈280 Wh kg^?1_{(cathode+anode)}) and energy efficiency (≈78%); furthermore, the results are comparable to those of state‐of‐the‐art lithium‐ion batteries.     

Quantum Physics and Deep Learning to Reveal Multiple Dimensional Modified Regulation by Ternary Substitution of Iron,Manganese, and Cobalt on Na3V2(PO4)3 for Superior Sodium Storage

Na₃V₂(PO₄)₃ is regarded as a promising candidate for sodium ion batteries. Nevertheless, the poor electronic conductivity, low capacities, and unstable structure limit its further investigations. Herein, a new type of Fe/Mn/Co co-substituted Na₃V₂(PO₄)₃ with nitrogen-doped carbon coating (NFMC) by a facile sol-gel route is synthesized. The introduced elements feature in both crystal bulk and carbon coating layer. Suitable heteroatom substitution activates more effective Na⁺ to participate in electrochemical process and reinforce the structure. An extra high voltage platform at 3.8 V resulting from the multi-element synergy (Mn²⁺/Mn³⁺/Mn⁴⁺; Co²⁺/Co³⁺; V⁴⁺/V⁵⁺) is stably and reversibly existed in NFMC to supply added capacities, which is investigated by quantum physics calculations. The high flux paths for Na⁺ migration and spin quantum state distribution in NFMC are demonstrated by molar magneton calculation. Significantly, the generated polyatomic coordination environment of M N C (M = Fe/Co/Mn) in carbon layer is first proposed. The most optimized combination structures are obtained from 69 possible structures and demonstrated by X-ray absorption spectroscopy. The superior electrochemical performance is precisely forecasted by innovative deep learning. Predicted values with high precision are obtained based on a small number of operating data, extremely short development period, and provide real-time status references for safer use.     

Weak Ionization Induced Interfacial Deposition and Transformation towards Fast-Charging NaTi2(PO4)3 Nanowire Bundles for Advanced Aqueous Sodium-Ion Capacitors

Aqueous sodium-ion capacitors (ASICs) offer great promise for inexpensive and safe energy storage. However, their development is plagued by a kinetics imbalance at high rates between battery and capacitive electrodes and a narrow voltage window due to water electrolysis. Here a unique nanowire bundles anode is designed that simultaneously affords ultrahigh rate capability and manifests robust Na⁺ insertion to suppress hydrogen evolution, enabling an advanced ASIC. The NaTi₂(PO₄)₃ (NTP) is grown on thin titanium foil by elaborately utilizing the weak ionization chemistry of NaH₂PO₄ (NHP), where single-agent NHP not only partially etches titanium to release TiO²⁺, but also induces the interfacial phase-transformation of pre-deposited orthomorphic Na₄Ti(PO₄)₂(OH)₂ cubes to hexagonal NTP nanowires. This anode has hierarchical architectures to facilitate charge and mass transport, thus working stably at considerably high rates of 15–150 C with high capacities. The first 2.4 V flexible solid-state NTP-based ASIC is designed with high energy densities (5.8–12.8 mWh cm⁻³; 57.9–62.1 Wh kg⁻¹; total mass loading up to 8.1 mg cm⁻²) comparable to NASICON-based devices using organic electrolytes, demonstrating outstanding stability of 10 000 cycles and no performance decay even after continuous bending at 180^o. This work presents a versatile strategy to construct NASICON phosphate electrodes for advanced energy storage.     

Cr^4＋：YAG在Nd^3＋准三能级跃迁波长的吸收截面

用泵浦探测法测量了Cr4+YAG在Nd3+准三能级4 F3/2-4 I9/2跃迁波长的基态和激发态吸收截面,其结果为在Nd3+YAG的准三能级跃迁波长946 nm处,基态和激发态吸收截面分别为4.0×10-18 cm2和1.1×10-18 cm2;在Nd3+YVO4的准三能级跃迁波长914 nm和Nd3+GdVO4的准三能级跃迁波长912 nm处,2个吸收截面分别为3.9×10-18 cm2和1.4×10-18 cm2.     

NaY（WO4）2：Yb^3＋,Er^3＋晶体的光学性质

用Czochralski方法生长了yb3+ ,Er3+共掺的NaY (WO4)2晶体.测量了晶体在室温下的吸收谱,用Judd-Ofelt理论计算了NaY (WO4)2 :Er3+ ,Yb3+晶体中Er3+的3个唯象强度参量Ω2=18.10×10-20、Ω4=2.59×10-20、Ω6=1.21×10-20和辐射跃迁特征参量.研究了晶体的荧光特性,并在974 nm的LD泵浦下得到上转换绿色荧光.分析了晶体中Yb3+向Er3+传递能量的机制.     

Bi2O3过量对熔盐法制备Bi4Ti3O12粉体的影响

以NaCl-KCl熔盐法制备了各向异性的Bi4Ti3O12粉体,研究了w(Bi2O3过量)对粉体的影响,优化了制备Bi4Ti3O12粉体的工艺参数。结果表明:w(Bi2O3过量)为7.5%,1100℃烧结2h所得到的Bi4Ti3O12粉体微观形貌最佳,并探讨了Bi4Ti3O12粉体在熔盐中的生长机理。     

优质大尺寸金绿宝石(Cr3+:BeAl2O4)可调谐激光晶体的生长

应用改进工艺的提拉(CZ)法技术,采用合适的化学组分配比和二次化料过程,选用约60℃的固液界面温度梯度与1mm/h生长速度等工艺参量,成功地生长出了Cr3 离子掺杂、无气泡、无云层和核心、长度与厚度约110×25mm的紫翠色Cr3 :BeAl2O4晶体。测定了晶体的吸收光谱,根据获得的吸收光谱与晶体分裂场理论,计算了Cr3 的八面体晶格场参数Dq=1764cm-1以及Racah参数B=608cm-1。晶体样品加工成6(60、80)mm的激光棒,并实现了激光的输出。     

Eu~(3+),Tb~(3+)共掺杂NaY(MoO_4)_2材料的制备及发光性能研究

采用水热法制备出NaY(MoO4)2:Eu3+,Tb3+下转换发光材料。通过X射线粉末衍射、红外光谱、荧光激发和发射光谱对其进行表征。讨论了不同反应温度及Eu3+掺杂浓度对NaY(MoO4)2:Eu3+,Tb3+的晶体结构和发光性能的影响,得到水热温度为180℃及Eu3+浓度为摩尔分数0.7%时,样品具有最佳的发光效果。在395nm光激发下,观察到了591nm处橙光发射峰以及616nm处强红光发射峰,分别对应于Eu3+的5D0→7F1和5D0→7F2跃迁。并研究了NaY(MoO4)2:Eu3+,Tb3+材料中Tb3+对Eu3+的敏化作用及能量传递过程。     

NBT-Ba(NbO3)2无铅压电陶瓷的压电介电性能

采用传统陶瓷制备方法,制备了一种新的(Na1/2Bi1/2)TiO3基无铅压电陶瓷(1-x)(Na1/2Bi1/2)TiO3-xBa(NbO3)2(摩尔分数x=0~1.4%)。X-射线衍射分析表明,所研究的组成均能够形成纯钙钛矿(ABO3)型固溶体。SEM观察结果表明,掺入Ba(NbO3)2促进了长条状晶粒的析出。不同频率下陶瓷材料的介电常数-温度曲线显示该体系材料具有明显的弛豫铁电体特征,且随着Ba(NbO3)2的增加,其弛豫性特征愈明显。检测了不同组成陶瓷的压电性能,发现材料的压电常数d33和平面机电耦合系数kp随着x值的增加先增加后降低,在x=0.6%时,陶瓷的d33=94 pC/N,kp=0.171,为所研究组成中的最大值,介电损耗tanδ则随x值的增加而增加。     

低温烧结(1–x)Ba_3(VO_4)_(2-x)Li_2WO_4微波介质陶瓷的研究

为了获得低温烧结的陶瓷材料,用固相反应制备了(1–x)Ba3(VO4)2-x Li2WO4(0.05≤x≤0.20)微波介质陶瓷。实验结果表明:随着添加剂Li2WO4的增加,复合陶瓷的相对体密度、相对介电常数εr和品质因数Q·f都呈现出先增加随后又降低的趋势,而谐振频率温度系数τf呈线性降低。添加了摩尔分数0.15Li2WO4的微波介质陶瓷在850℃烧结2 h达到约96.8%的致密度,并获得最佳的微波介电性能:εr=13.7,Q·f=97000 GHz,τf=1.8×10–6/℃。     

Nd~(3+)∶NaY(WO_4)_2晶体的激光性能研究

本文报道一种新型的激光晶体Nd~（3+）∶NaY（WO_4）2．测定了它的结构、荧光光谱、吸收光谱。用φ3mm×25mm2的小型脉冲觎灯泵浦φ3mm×5．95mm2的激光棒，获得22．5mJ的激光能量输出，物化性能好，是一种有良好应用前景的激光晶体．