RESUMEN
In this study, a novel approach is introduced to address the challenges associated with structural instability and sluggish reaction kinetics of δ-MnO2 in aqueous zinc ion batteries. By leveraging zwitterionic betaine (Bet) for intercalation, a departure from traditional cation intercalation methods, Bet-intercalated MnO2 (MnO2-Bet) is synthesized. The positively charged quaternary ammonium groups in Bet form strong electrostatic interactions with the negatively charged oxygen atoms in the δ-MnO2 layers, enhancing structural stability and preventing layer collapse. Concurrently, the negatively charged carboxylate groups in Bet facilitate the rapid diffusion of H+/Zn2+ ions through their interactions, thus improving reaction kinetics. The resulting MnO2-Bet cathode demonstrates high specific capacity, excellent rate capability, fast reaction kinetics, and extended cycle life. This dual-function intercalation strategy significantly optimizes the electrochemical performance of δ-MnO2, establishing it as a promising cathode material for advanced aqueous zinc ion batteries.
RESUMEN
The simultaneous intercalation of protons and Zn2+ ions in aqueous electrolytes presents a significant obstacle to the widespread adoption of aqueous zinc ion batteries (AZIBs) for large-scale use, a challenge that has yet to be overcome. To address this, we have developed a MnO2/tetramethylammonium (TMA) superstructure with an enlarged interlayer spacing, designed specifically to control H+/Zn2+ co-intercalation in AZIBs. Within this superstructure, the pre-intercalated TMA+ ions work as spacers to stabilize the layered structure of MnO2 cathodes and expand the interlayer spacing substantially by 28 % to 0.92 nm. Evidence from in operando pH measurements, in operando synchrotron X-ray diffraction, and X-ray absorption spectroscopy shows that the enlarged interlayer spacing facilitates the diffusion and intercalation of Zn2+ ions (which have a large ionic radius) into the MnO2 cathodes. This spacing also helps suppress the competing H+ intercalation and the formation of detrimental Zn4(OH)6SO4·5H2O, thereby enhancing the structural stability of MnO2. As a result, enhanced Zn2+ storage properties, including excellent capacity and long cycle stability, are achieved.
RESUMEN
Phase transitions of Mn-based cathode materials associated with the charge and discharge process play a crucial role on the rate capability and cycle life of zinc ion batteries. Herein, a microscopic electrochemical failure mechanism of Zn-MnO2 batteries during the phase transitions from δ-MnO2 to λ-ZnMn2O4 is presented via systematic first-principle investigation. The initial insertion of Zn2+ intensifies the rearrangement of Mn. This is completed by the electrostatic repulsion and co-migration between guest and host ions, leading to the formation of λ-ZnMn2O4. The Mn relocation barrier for the λ-ZnMn2O4 formation path with 1.09 eV is significantly lower than the δ-MnO2 re-formation path with 2.14 eV, indicating the irreversibility of the layered-to-spinel transition. Together with the phase transition, the rearrangement of Mn elevates the Zn2+ migration barrier from 0.31 to 2.28 eV, resulting in poor rate performance. With the increase of charge-discharge cycles, irreversible and inactive λ-ZnMn2O4 products accumulate on the electrode, causing continuous capacity decay of the Zn-MnO2 battery.
RESUMEN
Ni-rich cathodes with a radial ordered microstructure have been proved to enhance materials' structural stability. However, the construction process of radial structures has not yet been clearly elaborated. Herein, the formation process of radial structures induced by different doped elements has been systematically investigated. The advanced Electron Back Scatter Diffraction (EBSD) characterization reveals that W-doped materials are more likely to form a low-angle arrangement between crystal planes of the primary particles and exhibit twin growth during sintering than a B-doped cathode. The corresponding High Angle Annular Dark Field-Scanning Transmission Electron Microscopy (HAADF-STEM) analysis further proves that the twin growth induced by W doping can promote the migration of Li+. Simultaneously, the W-doped sample reduces the (003) plane surface energy and promotes the retention of the crystal plane, which can effectively alleviate the structural degradation caused by Li+ (de)intercalation. At a cut-off voltage of 4.6 V, the W-doped cathode displays a capacity retention rate of 94.1% after 200 cycles at 1C. This work unveils the influence of different element doping on the structure from the perspective of crystal plane orientation within primary particles and points out the importance of the exposure and orientation of the crystal plane of the particles.
RESUMEN
Mechanical energy harvesting using piezoelectric nanogenerators (PNGs) offers an attractive solution for driving low-power portable devices and self-powered electronic systems. Here, we designed an eco-friendly and flexible piezocomposite nanogenerator (c-PNG) based on H2(Zr0.1Ti0.9)3O7 nanowires (HZTO-nw) and Ba0.85Ca0.15Zr0.10Ti0.90O3 multipods (BCZT-mp) as fillers and polylactic acid (PLA) as a biodegradable polymer matrix. The effects of the applied stress amplitude, frequency and pressing duration on the electric outputs in the piezocomposite nanogenerator (c-PNG) device were investigated by simultaneous recording of the mechanical input and the electrical outputs. The fabricated c-PNG shows a maximum output voltage, current and volumetric power density of 11.5 V, 0.6 µA and 9.2 mW cm-3, respectively, under cyclic finger imparting. A high-pressure sensitivity of 0.86 V kPa-1 (equivalent to 3.6 V N-1) and fast response time of 45 ms were obtained in the dynamic pressure sensing. Besides this, the c-PNG demonstrates high-stability and durability of the electrical outputs for around three months, and can drive commercial electronics (charging capacitor, glowing light-emitting diodes and powering a calculator). Multi-physics simulations indicate that the presence of BCZT-mp is crucial in enhancing the piezoelectric response of the c-PNG. Accordingly, this work reveals that combining 1D and 3D fillers in a polymer composite-based PNG could be beneficial in improving the mechanical energy harvesting performances in flexible piezoelectric nanogenerators for application in electronic skin and wearable devices.
RESUMEN
Two-dimensional transition metal dichalcogenides are promising anode materials for Na ion batteries (NIBs). In this study, we carried out a comprehensive investigation to analyze the structural, electrochemical characteristics, and diffusion kinetics of bulk WX2(X = Se, Te) by employing first-principles calculation in the framework of density functional theory. We deeply studied the full intercalation of Na+in WX2and diagnosed NayX phase through conversion reaction mechanism. The voltage range of 2.05-0.48 V vs Na/Na+for NayWSe2and 2.26-0.65 V for NayWTe2(y= 0-3) have been noted. Density of states analysis showed metallic behavior of WX2(X = Se, Te) during sodiation. The facile pathways for Na+mobility through WX2have shown that tungsten dichalcogenides are inferred as excellent electrode material for NIBs.
RESUMEN
Natrium super ionic conductor (NASICON) materials providing attractive properties such as high ionic conductivity and good structural stability are considered as very promising materials for use as electrodes for lithium- and sodium-ion batteries. Herein, a new high-performance electrode material, Li0.5Ni0.5Ti1.5Fe0.5(PO4)3/C, was synthesized via the sol-gel method and was electrochemically tested as an anode for lithium ion batteries, providing enhanced electrochemical performance as a result of nickel substitution into the lithium site in the LiTi2(PO4)3 family of materials. The synthesized material showed good ionic conductivity, excellent structural stability, stable long-term cycling performance, and improved high rate cycling performance compared to LiTi2(PO4)3. The Li0.5Ni0.5Ti1.5Fe0.5(PO4)3/C electrode delivered reversible capacities of about 93 and 68% of its theoretical one at current rates of 0.1 C (6.42 mA·g-1) after 100 cycles and 5 C (320.93 mA·g-1) after 1000 cycles, respectively. Theoretically, three Li+ ions can be inserted into the vacancies of the Li0.5Ni0.5Ti1.5Fe0.5(PO4)3/C structure. However, when the electrode is discharged to 0.5 V, more than three Li+ ions are inserted into the NASICON structure, leading to its structural transformation, and thus to an irreversible electrochemical behavior after the first discharge process.
RESUMEN
Rechargeable sodium-ion batteries have recently attracted renewed interest as an alternative to Li-ion batteries for electric energy storage applications, because of the low cost and wide availability of sodium resources. Thus, the electrochemical energy storage community has been devoting increased attention to designing new cathode materials for sodium-ion batteries. Here we investigate P2- Na0.78Co1/2Mn1/3Ni1/6O2 as a cathode material for sodium ion batteries. The main focus is to understand the mechanism of the electrochemical performance of this material, especially differences observed in redox reactions at high potentials. Between 4.2 V and 4.5 V, the material delivers a reversible capacity which is studied in detail using advanced analytical techniques. In situ X-ray diffraction reveals the reversibility of the P2-type structure of the material. Combined soft X-ray absorption spectroscopy and resonant inelastic X-ray scattering demonstrates that Na deintercalation at high voltages is charge compensated by formation of localized electron holes on oxygen atoms.
RESUMEN
Ni0.5 Ti2 (PO4 )3 /C NASICON-type phosphate is introduced as a new anode material for lithium-ion batteries (LIBs). Ni0.5 Ti2 (PO4 )3 /C was synthesized through the sol-gel route and delivered some remarkable electrochemical performances. Specifically, the Ni0.5 Ti2 (PO4 )3 /C electrode demonstrates a high rate capability performance and delivers high reversible capacities ranging from 130â mAh g-1 to about 111â mAh g-1 at current rates ranging from 0.1â C to 5â C in the voltage window of 1.85-3â V (vs. Li+ /Li). In the same voltage range, the material reaches an initial capacity of 105â mAh g-1 with a capacity retention of about 82 % after 1000 cycles at the high current rate of 10â C. The electrodes are also tested in the wider voltage range of 0.5-3â V (vs. Li+ /Li) and show good reversibility and rate capability performance. Moreover, the Ni0.5 Ti2 (PO4 )3 /C electrodes enable fast Li+ diffusion (in the order of 10-13 â cm2 s-1 ) compared with other NASICON-type materials. As a result, a first discharge capacity of 480â mAh g-1 is reached.
RESUMEN
P2-type NaMO2 sodiated layered oxides with mixed transition metals are receiving considerable attention for use as cathodes in sodium-ion batteries. A study on solid solution (1 - y)P2-NaxCoO2-(y)P2-NaxMn2/3Ni1/3O2 (y = 0, 1/3, 1/2, 2/3, 1) reveals that changing the composition of the transition metals affects the resulting structure and the stability of pure P2 phases at various temperatures of calcination. For 0 ≤ y ≤ 1.0, the P2-NaxCo(1-y)Mn2y/3Niy/3O2 solid-solution compounds deliver good electrochemical performance when cycled between 2.0 and 4.2 V versus Na+/Na with improved capacity stability in long-term cycling, especially for electrode materials with lower Co content (y = 1/2 and 2/3), despite lower discharge capacities being observed. The (1/2)P2-NaxCoO2-(1/2)P2-NaxMn2/3Ni1/3O2 composition delivers a discharge capacity of 101.04 mAh g-1 with a capacity loss of only 3% after 100 cycles and a Coulombic efficiency exceeding 99.2%. Cycling this material to a higher cutoff voltage of 4.5 V versus Na+/Na increases the specific discharge capacity to ≈140 mAh g-1 due to the appearance of a well-defined high-voltage plateau, but after only 20 cycles, capacity retention declines to 88% and Coulombic efficiency drops to around 97%. In situ X-ray absorption near-edge structure measurements conducted on composition NaxCo1/2Mn1/3Ni1/6O2 (y = 1/2) in the two potential windows studied help elucidate the operating potential of each transition metal redox couple. It also reveals that at the high-voltage plateau, all of the transition metals are stable, raising the suspicion of possible contribution of oxygen ions in the high-voltage plateau.
RESUMEN
Worries about lithium supplies have led to the development of research on sodium batteries. Sodium-ion batteries are regarded as the next generation of energy-storage devices thanks to the generous resources of sodium. In spite of that, structural changes in the electrode materials remain the main challenge of this storage technology. NaCoO2 has been widely investigated as a competitive candidate for LiCoO2. It has been found that the electrochemical cycling curves of this material present numerous potential steps as a result of electronic transitions and/or structural ordering. From this standpoint, this paper reports a novel cathode material, Na2/3Co0.95Ti0.05O2, where 5% of cobalt was replaced by titanium, prepared via a facile solid-state route. The sodiation/desodiation mechanism of this layered material was investigated. Na//Na2/3Co0.95Ti0.05O2 exhibits a first initial capacity of 119 mAh/g in the potential window 2-4.2 V with less potential jumps in the potential versus capacity curve compared to NaCoO2. Genuinely, the electrochemistry of this material demonstrated a reversibility upon the insertion/desinertion process with low polarization. In situ synchrotron investigations on Na2/3Co0.95Ti0.05O2 reveal the occurrence of reversible ordered phases. Ex situ magic-angle-spinning NMR disclosed different environments around sodium starting from the pristine state to the end of charge.
RESUMEN
SnP2O7 was prepared by a sol-gel route. The structural changes of tin pyrophosphate during the electrochemical lithiation were followed by using in situ XRD measurements that reveal the existence of a crystalline phase at the beginning of the discharge process. Nevertheless, it becomes amorphous after the full discharge as a result of a conversion reaction leading to the formation of LixSny alloys. The electrochemical tests show a high capacity with high retention upon cycling. To better understand the reaction mechanism of SnP2O7 with Li, several techniques were applied, such as ex situ(119)Sn Mössbauer and ex situ(7)Li and (31)P NMR spectroscopies with which we can follow the changes in the local environment of each element during cycling.
RESUMEN
The cathode material P2-Nax Co2/3 Mn2/9 Ni1/9 O2, which could be used in Na-ion batteries, was investigated through synchrotron-based hard X-ray photoelectron spectroscopy (HAXPES). Nondestructive analysis was made through the electrode/electrolyte interface of the first electrochemical cycle to ensure access to information not only on the active material, but also on the passivation layer formed at the electrode surface and referred to as the solid permeable interface (SPI). This investigation clearly shows the role of the SPI and the complexity of the redox reactions. Cobalt, nickel, and manganese are all electrochemically active upon cycling between 4.5 and 2.0â V; all are in the 4+ state at the end of charging. Reduction to Co(3+), Ni(3+), and Mn(3+) occurs upon discharging and, at low potential, there is partial reversible reduction to Co(2+) and Ni(2+). A thin layer of Na2 CO3 and NaF covers the pristine electrode and reversible dissolution/reformation of these compounds is observed during the first cycle. The salt degradation products in the SPI show a dependence on potential. Phosphates mainly form at the end of the charging cycle (4.5â V), whereas fluorophosphates are produced at the end of discharging (2.0â V).
