Li–Ti Cation Mixing Enhanced Structural and Performance Stability of Li‐Rich Layered Oxide

Li‐rich layered metal oxides are one type of the most promising cathode materials in lithium‐ion batteries but suffer from severe voltage decay during cycling because of the continuous transition metal (TM) migration into the Li layers. A Li‐rich layered metal oxide Li_1.2Ti_0.26Ni_0.18Co_0.18Mn_0.18O₂ (LTR) is hereby designed, in which some of the Ti⁴⁺ cations are intrinsically present in the Li layers. The native Li–Ti cation mixing structure enhances the tolerance for structural distortion and inhibits the migration of the TM ions in the TMO₂ slabs during (de)lithiation. Consequently, LTR exhibits a remarkable cycling stability of 97% capacity retention after 182 cycles, and the average discharge potential drops only 90 mV in 100 cycles. In‐depth studies by electron energy loss spectroscopy and aberration‐corrected scanning transmission electron microscopy demonstrate the Li–Ti mixing structure. The charge compensation mechanism is uncovered with X‐ray absorption spectroscopy and explained with the density function theory calculations. These results show the superiority of introducing transition metal ions into the Li layers in reinforcing the structural stability of the Li‐rich layered metal oxides. These findings shed light on a possible path to the development of Li‐rich materials with better potential retention and a longer lifespan.     

Atomic Sn4+ Decorated into Vanadium Carbide MXene Interlayers for Superior Lithium Storage

Ion intercalation is an important way to improve the energy storage performance of 2D materials. The dynamic energy storage process in such layered intercalations is important but still a challenge mainly due to the lack of effective operando methods. Herein, a unique atomic Sn⁴⁺–decorated vanadium carbide (V₂C) MXene not only exhibiting highly enhanced lithium‐ion battery (LIB) performance, but also possessing outstanding rate and cyclic stability because of the expanded interlayer space and the formation of V? O? Sn bonding is demonstrated. In combination with ex situ tests, an operando X‐ray absorption fine structure measurement is developed to explore the dynamic mechanism of V₂C@Sn MXene electrodes in LIBs. The results clearly reveal the valence changes of vanadium (V), tin (Sn), and positive contribution of oxygen (O) atoms during the charging/discharging process, confirming their contribution for lithium storage capacity. The stability of intercalated MXene electrode is further in situ studied to prove the key role of V? O? Sn bonding.     

Fundamental Understanding of Photocurrent Hysteresis in Perovskite Solar Cells

Organic–inorganic hybrid perovskite solar cells (PSCs) have become a promising candidate in the photovoltaic field due to their high power conversion efficiency and low material cost. However, the development of PSCs is limited by their poor stability under practical conditions in the presence of oxygen, moisture, sunlight, heat, and the current–voltage (I–V) hysteresis. In particular, the hysteretic I–V issue casts doubt on the validity of the photovoltaic performance results that are achieved, making it difficult to evaluate the authentic performance of PSCs. This review article focuses on understanding the I–V hysteresis behavior in PSCs and on exploring the possible reasons leading to this hysteresis phenomenon. The various strategies attempted to suppress the I–V hysteresis in PSCs are summarized, and a brief future recommendation is provided.     

Confined Fe2VO4⊂Nitrogen‐Doped Carbon Nanowires with Internal Void Space for High‐Rate and Ultrastable Potassium‐Ion Storage

Developing low‐cost, high‐capacity, high‐rate, and robust earth‐abundant electrode materials for energy storage is critical for the practical and scalable application of advanced battery technologies. Herein, the first example of synthesizing 1D peapod‐like bimetallic Fe₂VO₄ nanorods confined in N‐doped carbon porous nanowires with internal void space (Fe₂VO₄?NC nanopeapods) as a high‐capacity and stable anode material for potassium‐ion batteries (KIBs) is reported. The peapod‐like Fe₂VO₄?NC nanopeapod heterostructures with interior void space and external carbon shell efficiently prevent the aggregation of the active materials, facilitate fast transportation of electrons and ions, and accommodate volume variation during the cycling process, which substantially boosts the rate and cycling performance of Fe₂VO₄. The Fe₂VO₄?NC electrode exhibits high reversible specific depotassiation capacity of 380 mAh g^?1 at 100 mA g^?1 after 60 cycles and remarkable rate capability as well as long cycling stability with a high capacity of 196 mAh g^?1 at 4 A g^?1 after 2300 cycles. The first‐principles calculations reveal that Fe₂VO₄?NC nanopeapods have high ionic/electronic conductivity characteristics and low diffusion barriers for K⁺‐intercalation. This study opens up new way for investigating high‐capacity metal oxide as high‐rate and robust electrode materials for KIBs.     

A High‐Performance Monolithic Solid‐State Sodium Battery with Ca2+ Doped Na3Zr2Si2PO12 Electrolyte

Solid‐state sodium batteries (SSSBs) are promising electrochemical energy storage devices due to their high energy density, high safety, and abundant resource of sodium. However, low conductivity of solid electrolyte as well as high interfacial resistance between electrolyte and electrodes are two main challenges for practical application. To address these issues, pure phase Na₃Zr₂Si₂PO₁₂ (NZSP) materials with Ca²⁺ substitution for Zr⁴⁺ are synthesized by a sol‐gel method. It shows a high ionic conductivity of more than 10^?3 S cm^?1 at 25 °C. Moreover, a robust SSSB is developed by integrating sodium metal anodes into NZSP‐type monolithic architecture, forming a 3D electronic and ionic conducting network. The interfacial resistance is remarkably reduced and the monolithic symmetric cell displays stable sodium platting/striping cycles with low polarization for over 600 h. Furthermore, by combining sodium metal anode with Na₃V₂(PO₄)₃ cathode, an SSSB is demonstrated with high rate capability and excellent cyclability. After 450 cycles, the capacity of the cell is still kept at 94.9 mAh g^?1 at 1 C. This unique design of monolithic electrolyte architecture provides a promising strategy toward realizing high‐performance SSSBs.     

Na3V2(PO4)3 as the Sole Solid Energy Storage Material for Redox Flow Sodium‐Ion Battery

Redox flow batteries have considerable advantages of system scalability and operation flexibility over other battery technologies, which makes them promising for large‐scale energy storage application. However, they suffer from low energy density and consequently relatively high cost for a nominal energy output. Redox targeting–based flow batteries are employed by incorporating solid energy storage materials in the tank and present energy density far beyond the solubility limit of the electrolytes. The success of this concept relies on paring suitable redox mediators with solid materials for facilitated reaction kinetics and lean electrolyte composition. Here, a redox targeting‐based flow battery system using the NASICON‐type Na₃V₂(PO₄)₃ as a capacity booster for both the catholyte and anolyte is reported. With 10‐methylphenothiazine as the cathodic redox mediator and 9‐fluorenone as anodic redox mediator, an all‐organic single molecule redox targeting–based flow battery is developed. The anodic and cathodic capacity are 3 and 17 times higher than the solubility limit of respective electrolyte, with which a full cell can achieve an energy density up to 88 Wh L^?1. The reaction mechanism is scrutinized by operando and in‐situ X‐ray and UV–vis absorption spectroscopy. The reaction kinetics are analysed in terms of Butler–Volmer formalism.     

Thermally Durable Lithium‐Ion Capacitors with High Energy Density from All Hydroxyapatite Nanowire‐Enabled Fire‐Resistant Electrodes and Separators

The reliability and durability of lithium‐ion capacitors (LICs) are severely hindered by the kinetic imbalance between capacitive and Faradaic electrodes. Efficient charge storage in LICs is still a huge challenge, particularly for thick electrodes with high mass loading, fast charge delivery, and harsh working conditions. Here, a unique thermally durable, stable LIC with high energy density from all‐inorganic hydroxyapatite nanowire (HAP NW)‐enabled electrodes and separators is reported. Namely, the LIC device is designed and constructed with the electron/ion dual highly conductive and fire‐resistant composite Li₄Ti₅O₁₂‐based anode and activated carbon‐based cathode, together with a thermal‐tolerant HAP NW separator. Despite the thick‐electrode configuration, the as‐fabricated all HAP NW‐enabled LIC exhibits much enhanced electrochemical kinetics and performance, especially at high current rates and temperatures. Long cycling lifetime and state‐of‐the‐art areal energy density (1.58 mWh cm^?2) at a high mass loading of 30 mg cm^?2 are achieved. Benefiting from the excellent fire resistance of HAP NWs, such an unusual LIC exhibits high thermal durability and can work over a wide range of temperatures from room temperature to 150 °C. Taking full advantage of synergistic configuration design, this work sets the stage for designing advanced LICs beyond the research of active materials.     

Co–B Nanoflakes as Multifunctional Bridges in ZnCo2O4 Micro‐/Nanospheres for Superior Lithium Storage with Boosted Kinetics and Stability

Transition metal oxides hold great promise as high‐energy anodes in next‐generation lithium‐ion batteries. However, owing to the inherent limitations of low electronic/ionic conductivities and dramatic volume change during charge/discharge, it is still challenging to fabricate practically viable compacted and thick TMO anodes with satisfactory electrochemical performance. Herein, with mesoporous cobalt–boride nanoflakes serving as multifunctional bridges in ZnCo₂O₄ micro‐/nanospheres, a compacted ZnCo₂O₄/Co–B hybrid structure is constructed. Co–B nanoflakes not only bridge ZnCo₂O₄ nanoparticles and function as anchors for ZnCo₂O₄ micro‐/nanospheres to suppress the severe volume fluctuation, they also work as effective electron conduction bridges to promote fast electron transportation. More importantly, they serve as Li⁺ transfer bridges to provide significantly boosted Li⁺ diffusivity, evidenced from both experimental kinetics analysis and density functional theory calculations. The mesopores within Co–B nanoflakes help overcome the large Li⁺ diffusion barriers across 2D interfaces. As a result, the ZnCo₂O₄/Co–B electrode delivers high gravimetric/volumetric/areal capacities of 995 mAh g^?1/1450 mAh cm^?3/5.10 mAh cm^?2, respectively, with robust rate capability and long‐term cyclability. The distinct interfacial design strategy provides a new direction for designing compacted conversion‐type anodes with superior lithium storage kinetics and stability for practical applications.