Natriumionenbatterien für die elektrochemische Energiespeicherung

Designing Solvated Double-Layer Polymer Electrolytes with Molecular Interactions Mediated Stable Interfaces for Sodium Ion Batteries

Unstable cathode-electrolyte and/or anode-electrolyte interface in polymer-based sodium-ion batteries (SIBs) will deteriorate their cycle performance. Herein, a unique solvated double-layer quasi-solid polymer electrolyte (SDL-QSPE) with high Na⁺ ion conductivity is designed to simultaneously improve stability on both cathode and anode sides. Different functional fillers are solvated with plasticizers to improve Na⁺ conductivity and thermal stability. The SDL-QSPE is laminated by cathode- and anode-facing polymer electrolyte to meet the independent interfacial requirements of the two electrodes. The interfacial evolution is elucidated by theoretical calculations and 3D X-ray microtomography analysis. The Na_0.67 Mn_2/3 Ni_1/3 O₂ |SDL-QSPE|Na batteries exhibit 80.4 mAh g^-1 after 400 cycles at 1 C with the Coulombic efficiency close to 100 %, which significantly outperforms those batteries using the monolayer-structured QSPE.

Lithiation and Sodiation of Hydrogenated Silicene: A Density Functional Theory Investigation

The next-generation renewable energy machineries necessitate the electrodes with appropriate electrochemical performance. Here, the anodic properties of silicane for Li- and Na-ion batteries were scrutinized employing first-principle calculations. The projected single-layer hydrogen-functionalized Si (Si₂ H₂ ) structure was energetically, mechanically, dynamically, and thermally stable based on theoretical simulations, confirming its experimental feasibility. The electronic properties revealed the semiconducting nature of silicane on the basis of PBE and HSE06 schemes with an indirect bandgap. As anode material for Li- and Na-ion batteries, hydrogenated silicene showed promising electrochemical performance because of the proper adsorption strength between Si₂ H₂ and the adsorbed Li and Na. The average open circuit voltages for Li_2x Si₂ H₂ and Na_2x Si₂ H₂ were as low as 0.42 and 0. 64 V, while its specific capacity was as high as 921 and 1842 mAh g^-1 for Li and Na, respectively. It also showed ultra-fast diffusion channels for Li and Na ions. The diffusion barriers for Li and Na migrations were as low as 0.18 and 0.14 eV, respectively, which revealed rapid charge/discharge processes using hydrogenated silicene as anode. These important features facilitate silicane as favorable anode material for Li/Na-ion batteries.

Pinning Effect Enhanced Structural Stability toward a Zero-Strain Layered Cathode for Sodium-Ion Batteries

Layered oxides as the cathode materials of sodium-ion batteries are receiving extensive attention due to their high capacity and flexible composition. However, the layered cathode tends to be thermodynamically and electrochemically unstable during (de)sodiation. Herein, we propose the pinning effect and controllable pinning point in sodium storage layered cathodes to enhance the structural stability and achieve optimal electrochemical performance. 0 %, 2.5 % and 7.3 % transition-metal occupancies in Na-site as pinning points are obtained in Na_0.67 Mn_0.5 Co_0.5-x Fe_x O₂ . 2.5 % Na-site pinned by Fe³⁺ is beneficial to restrain the potential slab sliding and enhance the structural stability, resulting in an ultra-low volume variation of 0.6 % and maintaining the smooth two-dimensional channel for Na-ion transfer. The Na_0.67 Mn_0.5 Co_0.4 Fe_0.1 O₂ cathode with the optimal Fe³⁺ pinning delivers outstanding cycle performance of over 1000 cycles and superior rate capability up to 10 C.

The Development of Vanadyl Phosphate Cathode Materials for Energy Storage Systems: A Review

Various cathode materials have been proposed for high-performance rechargeable batteries. Vanadyl phosphate is an important member of the polyanion cathode family. VOPO₄ has seven known crystal polymorphs with tunneled or layered frameworks, which allow facile cation (de)intercalations. Two-electron transfer per formula unit can be realized by using V^V /V^IV and V^IV /V^III redox couples. The electrochemical performance is closely related to the structures of VOPO₄ and the types of inserted cations. This Review outlines the crystal structures of VOPO₄ polymorphs and their lithiated phases. The research progress of vanadyl phosphate cathode materials for different energy storage systems, including lithium-ion batteries, sodium-ion batteries, potassium-ion batteries, multivalent batteries, and supercapacitors, as well as the related mechanism investigations are summarized. It is hoped that this Review will help with future directions of using vanadyl phosphate materials for energy storage.

A Black Phosphorus-Graphite Composite Anode for Li-/Na-/K-Ion Batteries

Black phosphorus (BP) is a desirable anode material for alkali metal ion storage owing to its high electronic/ionic conductivity and theoretical capacity. In-depth understanding of the redox reactions between BP and the alkali metal ions is key to reveal the potential and limitations of BP, and thus to guide the design of BP-based composites for high-performance alkali metal ion batteries. Comparative studies of the electrochemical reactions of Li⁺ , Na⁺ , and K⁺ with BP were performed. Ex situ X-ray absorption near-edge spectroscopy combined with theoretical calculation reveal the lowest utilization of BP for K⁺ storage than for Na⁺ and Li⁺ , which is ascribed to the highest formation energy and the lowest ion diffusion coefficient of the final potassiation product K₃ P, compared with Li₃ P and Na₃ P. As a result, restricting the formation of K₃ P by limiting the discharge voltage achieves a gravimetric capacity of 1300 mAh g^-1 which retains at 600 mAh g^-1 after 50 cycles at 0.25 A g^-1 .

Bilayered Potassium Vanadate K0.5 V2 O5 as Superior Cathode Material for Na-Ion Batteries

A bilayered potassium vanadate K_0.5 V₂ O₅ (KVO) is synthesized by a fast and facile synthesis route and evaluated as a positive electrode material for Na-ion batteries. Half the potassium ions can be topotactically extracted from KVO through the first charge, allowing 1.14 Na⁺ ions to be reversibly inserted. A good rate capability is also highlighted, with 160 mAh g^-1 at C/10, 94 mAh g^-1 at C/2, 73 mAh g^-1 at 2C and excellent cycling stability with 152 mAh g^-1 still available after 50 cycles at C/10. Ex situ X-ray diffraction reveals weak and reversible structural changes resulting in soft breathing of the KVO host lattice upon Na extraction-insertion cycles (ΔV/V≈3 %). A high structure stability upon cycling is also achieved, at both the long-range order and atomic scale probed by Raman spectroscopy. This remarkable behavior is ascribed to the large interlayer spacing of KVO (≈9.5 Å) stabilized by pillar K ions, which is able to accommodate Na ions without any critical change to the structure. Kinetics measurements reveal a good Na diffusivity that is hardly affected upon discharge. This study opens an avenue for further exploration of potassium vanadates and other bronzes in the field of Na-ion batteries.

Sulfur-/Nitrogen-Rich Albumen Derived "Self-Doping" Graphene for Sodium-Ion Storage

The development of sodium-ion batteries (SIBs) is hindered by the rapid reduction in reversible capacity of carbon-based anode materials. Outside-in doping of carbon-based anodes has been extensively explored. Nickel and NiS₂ particles embedded in nitrogen and sulfur codoped porous graphene can significantly improve the electrochemical performance. Herein a built-in heteroatom "self-doping" of albumen-derived graphene for sodium storage is reported. The built-in sulfur and nitrogen in albumen act as the doping source during the carbonization of proteins. The sulfur-rich proteins in albumen can also guide the doping and nucleation of nickel sulfide nanoparticles. Additionally, the porous architecture of the carbonized proteins is achieved through removable KCl/NaCl salts (medium) under high-temperature melting conditions. During the carbonization process, nitrogen can also reduce the carbonization temperature of thermally stable carbon materials. In this work, the NS-graphene delivered a specific capacity of 108.3 mAh g^-1 after 800 cycles under a constant current density of 500 mA g^-1 . In contrast, the Ni/NiS₂ /NS-graphene maintained a specific capacity of 134.4 mAh g^-1 ; thus the presence of Ni/NiS₂ particles improved the electrochemical performance of the whole composite.

Designed One-Pot Strategy for Dual-Carbon-Protected Na3 V2 (PO4 )3 Hybrid Structure as High-Rate and Ultrastable Cathode for Sodium-Ion Batteries

Sodium-ion batteries have attracted tremendous attention due to their much lower cost and similar working principle compared with lithium-ion batteries, which have been invited great expectation as energy storage devices in grid-level applications. The sodium superionic conductor Na₃ V₂ (PO₄ )₃ has been considered as a promising cathode candidate; however, its intrinsic low electronic conductivity results in poor rate performance and unsatisfactory cycling performance, which severely impedes its potential for practical applications. Herein, we developed a facile one-pot strategy to construct dual carbon-protected hybrid structure composed of carbon coated Na₃ V₂ (PO₄ )₃ nanoparticles embedded with carbon matrix with excellent rate performance, superior cycling stability and ultralong lifespan. Specifically, it can deliver an outstanding rate performance with a 51.5 % capacity retention from 0.5 to 100 C and extraordinary cycling stability of 80.86 % capacity retention after 6000 cycles at the high rate of 20 C. The possible reasons for the enhanced performance could be understood as the synergistic effects of the strengthened robust structure, facilitated charge transfer kinetics, and the mesoporous nature of the Na₃ V₂ (PO₄ )₃ hybrid structure. This work provides a cost-effective strategy to effectively optimize the electrochemical performance of a Na₃ V₂ (PO₄ )₃ cathode, which could contribute to push forward the advance of its practical applications.

A Four-Electron Sulfur Electrode Hosting a Cu2+ /Cu+ Redox Charge Carrier

The elemental sulfur electrode with Cu²⁺ as the charge carrier gives a four-electron sulfur electrode reaction through the sequential conversion of S↔CuS↔Cu₂ S. The Cu-S redox-ion electrode delivers a high specific capacity of 3044 mAh g^-1 based on the sulfur mass or 609 mAh g^-1 based on the mass of Cu₂ S, the completely discharged product, and displays an unprecedently high potential of sulfur/metal sulfide reduction at 0.5 V vs. SHE. The Cu-S electrode also exhibits an extremely low extent of polarization of 0.05 V and an outstanding cycle number of 1200 cycles retaining 72 % of the initial capacity at 12.5 A g^-1 . The remarkable utility of this Cu-S cathode is further demonstrated in a hybrid cell that employs an Zn metal anode and an anion-exchange membrane as the separator, which yields an average cell discharge voltage of 1.15 V, the half-cell specific energy of 547 Wh kg^-1 based on the mass of the Cu₂ S/carbon composite cathode, and stable cycling over 110 cycles.

Can Metallic Sodium Electrodes Affect the Electrochemistry of Sodium-Ion Batteries? Reactivity Issues and Perspectives

Sodium-ion batteries (NIBs) are promising energy-storage devices with advantages such as low cost and highly abundant raw materials. To probe the electrochemical properties of NIBs, sodium metal is most frequently applied as the reference and/or counter electrode in state-of-the-art literature. However, the high reactivity of the sodium metal and its impact on the electrochemical performance is usually neglected. In this study, it is shown that spontaneous reactions of sodium metal with organic electrolytes and the importance of critical interpretation of electrochemical experiments is emphasized. When using sodium-metal half-cells, decomposition products contaminate the electrolyte during the electrochemical measurement and can easily lead to wrong conclusions about the stability of the active materials. The cycling stability is highly affected by these electrolyte contaminations, which is proven by comparing sodium-metal-free cell with sodium-metal-containing cells. Interestingly, a more stable cycling performance of the Li₄ Ti₅ O₁₂ half-cells can be observed when replacing the Na metal counter and reference electrodes with activated carbon electrodes. This difference is attributed to the altered properties of the electrolyte as a result of contamination and to different surface chemistries.

A Dual-Ion Organic Symmetric Battery Constructed from Phenazine-Based Artificial Bipolar Molecules

Symmetric batteries received an increasing research interest in the past few years because of their simplified fabrication process and reduced manufacturing cost. In this study, we propose the first dual-ion organic symmetric cell based on a molecular anion of 4,4'-(phenazine-5,10-diyl)dibenzoate. The alkali salt of 4,4'-(phenazine-5,10-diyl)dibenzoate allows a facile transport of cations and large anions, and remains stable in both oxidized and reduced states. The large potential difference between phenazine and benzoate results in a high cell voltage of 2.5 V and an energy density of 127 Wh kg^-1 at a current rate of 1 C. The introduction of bipolar organic materials may further consolidate the development of symmetric batteries that are fabricated from abundant elements and environmentally friendly materials.

Nitrogen/Oxygen Co-Doped Hierarchically Porous Carbon for High-Performance Potassium Storage

Although the insertion of potassium ions into graphite has been proven to be realistic, the electrochemical performance of potassium-ion batteries (PIBs) is not yet satisfactory. Therefore, more effort is required to improve the specific capabilities and achieve a long cycling life. The mild carbonization process in molten salt (NaCl-KCl) is used to synthesize nitrogen/oxygen co-doped hierarchically porous carbon (NOPC) for PIBs by using cyanobacteria as the carbon source. This exhibits highly reversible capacities and ultra-long cycling stability, retaining a capacity of 266 mA h g^-1 at 50 mA g^-1 (100 cycles) and presents a capacity of 104.3 mA h g^-1 at 1000 mA g^-1 (1000 cycles). Kinetics analysis reveals that the potassium ion (K⁺ ) storage of NOPC is controlled by a capacitive process, which plays a crucial role in the excellent rate performance and superior reversible ability. The high proportion of capacitive behavior can be ascribed to the hierarchically porous structure and improved conductivity resulting from nitrogen and oxygen doping. Furthermore, density functional theory (DFT) calculations theoretically validate the enhanced potassium storage effect of the as-obtained NOPC. More importantly, the route to NOPC from cyanobacteria in molten salt provides a green approach to the synthesis of porous carbon materials.

Hard Carbon as Sodium-Ion Battery Anodes: Progress and Challenges

Hard carbon (HC) is the state-of-the-art anode material for sodium-ion batteries due to its excellent overall performance, wide availability, and relatively low cost. Recently, tremendous effort has been invested to elucidate the sodium storage mechanism in HC, and to explore synthetic approaches that can enhance the performance and lower the cost. However, disagreements remain in the field, particularly on the fundamental questions of ion transfer and storage and the ideal HC structure for high performance. This Minireview aims to provide an analysis and summary of the theoretical limitations of HC, discrepancies in the storage mechanism, and methods to improve the performance. Finally, future research on developing ideal structured HCs, advanced electrolytes, and optimized electrolyte-electrode interphases are proposed on the basis of recent progress.

A Multi-Ion Strategy towards Rechargeable Sodium-Ion Full Batteries with High Working Voltage and Rate Capability

Sodium-ion batteries (SIBs) are a promising alternative for the large-scale energy storage owing to the natural abundance of sodium. However, the practical application of SIBs is still hindered by the low working voltage, poor rate performance, and insufficient cycling stability. A sodium-ion based full battery using a multi-ion design is now presented. The optimized full batteries delivered a high working voltage of about 4.0 V, which is the best result of reported sodium-ion full batteries. Moreover, this multi-ion battery exhibited good rate performance up to 30 C and a high capacity retention of 95 % over 500 cycles at 5 C. Although the electrochemical performance of this multi-ion battery may be further enhanced via optimizing electrolyte and electrode materials for example, the results presented clearly indicate the feasibility of this multi-ion strategy to improve the electrochemical performance of SIBs for possible energy storage applications.

Partial Substitution of Potassium with Sodium in the K2Ti2(PO4)3 Langbeinite-Type Framework: Synthesis and Crystalline Structure of K1.75Na0.25Ti2(PO4)3

The interaction of TiN with Na2O-K2O-P2O5 melts was investigated at (Na+K)/P molar ratios of 0.9, 1.0, and 1.2 and at Na/K molar ratios of 1.0 and 2.0. Interactions in the system led to the loss of nitrogen and the partial loss of phosphorus and resulted in the formation of KTiP2O7 and langbeinite-type K2-x Na x Ti2(PO4)3 (x=0.22-0.26) solid solutions over the temperature range of 1173 to 1053 K. The phase compositions of the obtained samples were determined by using X-ray diffraction (including Rietveld refinement), scanning electron microscopy (using energy-dispersive X-ray spectroscopy and element mapping), FTIR spectroscopy, and thermogravimetric analysis/differential thermal analysis. K1.75Na0.25Ti2(PO4)3 was characterized by single-crystal X-ray diffraction [P213 space group, a=9.851(5) Å]. The 3D framework is built up by TiO6 octahedra and PO4 tetrahedra sharing all the oxygen vertices with the formation of cavities occupied by K(Na) cations. Only one of the two crystallographically inequivalent potassium sites is partially substituted by sodium, and this was confirmed by calculating the bond-valence sum. The thermodynamic stability of K1.75Na0.25Ti2(PO4)3 crystals and the preferable occupation sites of NaK cationic substitutions were investigated by DFT-based electronic structure calculations performed by the plane-wave pseudopotential method.

Redox Chemistry of Molybdenum Trioxide for Ultrafast Hydrogen-Ion Storage

Hydrogen ions are ideal charge carriers for rechargeable batteries due to their small ionic radius and wide availability. However, little attention has been paid to hydrogen-ion storage devices because they generally deliver relatively low Coulombic efficiency as a result of the hydrogen evolution reaction that occurs in an aqueous electrolyte. Herein, we successfully demonstrate that hydrogen ions can be electrochemically stored in an inorganic molybdenum trioxide (MoO₃ ) electrode with high Coulombic efficiency and stability. The as-obtained electrode exhibits ultrafast hydrogen-ion storage properties with a specific capacity of 88 mA hg^-1 at an ultrahigh rate of 100 C. The redox reaction mechanism of the MoO₃ electrode in the hydrogen-ion cell was investigated in detail. The results reveal a conversion reaction of the MoO₃ electrode into H_0.88 MoO₃ during the first hydrogen-ion insertion process and reversible intercalation/deintercalation of hydrogen ions between H_0.88 MoO₃ and H_0.12 MoO₃ during the following cycles. This study reveals new opportunities for the development of high-power energy storage devices with lightweight elements.

Robust SnO2-x Nanoparticle-Impregnated Carbon Nanofibers with Outstanding Electrochemical Performance for Advanced Sodium-Ion Batteries

The sluggish sodium reaction kinetics, unstable Sn/Na₂ O interface, and large volume expansion are major obstacles that impede practical applications of SnO₂ -based electrodes for sodium-ion batteries (SIBs). Herein, we report the crafting of homogeneously confined oxygen-vacancy-containing SnO_2-x nanoparticles with well-defined void space in porous carbon nanofibers (denoted SnO_2-x /C composites) that address the issues noted above for advanced SIBs. Notably, SnO_2-x /C composites can be readily exploited as the working electrode, without need for binders and conductive additives. In contrast to past work, SnO_2-x /C composites-based SIBs show remarkable electrochemical performance, offering high reversible capacity, ultralong cyclic stability, and excellent rate capability. A discharge capacity of 565 mAh g^-1 at 1 A g^-1 is retained after 2000 cycles.