Advances in Nanomaterials for Lithium-Ion/Post-Lithium-Ion Batteries and Supercapacitors

Energy storage and conversion are key factors for enabling the transition from fossil fuels to intermittent renewables [...

Study of polyoxometalates as electrode materials for Li‐ion batteries: Thermal stability paves the way to an improved cycle stability

Polyoxometallates (POMs) are ideal candidates for energy storage because of their multi‐electron transfer. (n‐Bu4N)3PW12O40 (TBA‐PW) and Cs3PW12O40 (Cs‐PW), prepared by proton‐exchange with tetrabutylammonium (TBA+) and cesium (Cs+) from H3PW12O40, suffer from serious capacity fading, owing to the contained crystal water. The presence of water in POMs is well known, but its effect on electrochemical performance is not reported yet. In contrast to TBA‐PW, Cs‐PW has a higher thermal stability and can be treated at 600 °C, which allows the complete water removal (Cs‐PW‐600). Cs‐PW‐600 has a 15‐times better cycling performance than the one dried at 120 °C. Different pressures were applied to optimize the electrode fabrication. Samples treated at 8 tons show a three‐times better rate capability with respect to the unpressed sample, with 42.8 % retention of the capacity at 200 mA g−1. Cs‐PW‐600 can be seen as an example for further investigations on POMs as electrode materials

Effect of Continuous Capacity Rising Performed by FeS/Fe₃C/C Composite Electrodes for Lithium‐Ion Batteries

FeS‐based composites are sustainable conversion electrode materials for lithium‐ion batteries, combining features like low cost, environmental friendliness, and high capacities. However, they suffer from fast capacity decay and low electron conductivity. Herein, novel insights into a surprising phenomenon of this material are provided. A FeS/Fe3C/C nanocomposite synthesized by a facile hydrothermal method is compared with pure FeS. When applied as anode materials for lithium‐ion batteries, these two types of materials show different capacity evolution upon cycling. Surprisingly, the composite delivers a continuous increase in capacity instead of the expected capacity fading. This unique behavior is triggered by a catalyzing effect of Fe3C nanoparticles. The Fe3C phase is a beneficial byproduct of the synthesis and was not intentionally obtained. To further understand the effect of interconnected carbon balls on FeS‐based electrodes, complementary analytic techniques are used. Ex situ X‐ray radiation diffraction and ex situ scanning electron microscopy are employed to track phase fraction and morphology structure. In addition, the electrochemical kinetics and resistance are evaluated by cyclic voltammetry and electrochemical impedance spectroscopy. These results reveal that the interconnected carbon balls have a profound influence on the properties of FeS‐based electrodes resulting in an increased electrode conductivity, reduced particle size, and maintenance of the structure integrity

Are Functional Groups Beneficial or Harmful on the Electrochemical Performance of Activated Carbon Electrodes?

It is a common opinion that activated carbon (AC) should be functional groups-free when employed as capacitor-type material in organic electrolytes. This work analyzes in detail the relationship between the electrochemical performance of modified activated carbon electrodes and the introduced functional groups in two organic electrolytes containing lithium salts:1M LiPF6 in EC-DMC (the commercial LP30) and 1M LiTFSI in EC-DMC. The surface functional groups (especially C=O or O–C=O) can induce higher capacitance to AC (more than 50% increase compared to commercial unmodified AC), whereas the rate capability dramatically decreases. The appropriate amount of functional groups is helpful to expand the electrochemical stability window in LP30 (2.8–2.9 V), that is responsible for the high energy and power density. Moreover, the proper functional groups inhibit the potential shift of the AC electrode. However, a large number of functionalities can result in a high amount of irreversible redox products remaining in the pores of AC, which leads to a faster capacitance fade respect to materials with less functional groups

Oxide Spinels with Superior Mg Conductivity

Mg batteries with oxide cathodes have the potential to significantly surpass existing Li-ion technologies in terms of sustainability, abundance, and energy density. However, Mg intercalation at the cathode is often severely hampered by the sluggish kinetics of Mg$^{2+}$ migration within oxides. Here we report a combined theoretical and experimental study addressing routes to identify cathode materials with an improved Mg-ion mobility. Using periodic density functional theory calculations, Mg$^{2+}$ migration in oxide spinels has been studied, revealing key features that influence the activation energy for M$^{g2}$+ migration. Furthermore, the electronic and geometrical properties of the oxide spinels as well as their stability have been analyzed for a series of different transition metals in the spinels. We find that electronegative transition metals enable a high Mg-ion mobility in the oxide spinel frameworks and thus a favorable cathode functionality. Based on the theoretical findings, some promising candidates have been identified, prepared and structurally characterized. Our combined theoretical and experimental findings open up an avenue toward the utilization of functional cathode materials with improved Mg$^{2+}$ transport properties for Mg-metal batteries

An asymmetric MnO2_{2}|activated carbon supercapacitor with highly soluble choline nitrate-based aqueous electrolyte for sub-zero temperatures

MnO2|activated carbon supercapacitors are attractive power devices that rival the electric double-layer capacitors (EDLCs) due to high reachable voltage. However, they greatly suffer from performance loss at low temperature as most of aqueous electrolytes freeze below ca. -10°C. Here, a concentrated choline nitrate-based (5 mol/L aqueous ChNO$_{3}$) electrolyte is applied to extend the working temperature range due to its eutectic-like properties. In such electrolyte, water acts as hydrogen bond donor for nitrate anion and low hydration energy for large choline cations favors ionic transport. The MnO$_{2}$/CNT composite electrode with a hierarchical structure has been synthesized by hydrothermal process. The presence of CNTs as core component facilitates the electron conduction, while the two-dimensional MnO$_{2}$ flakes grown on the surface provide electrolyte transport pathways and improve the interfacial processes (pseudocapacitive charge/discharge). Thanks to the low hydration of choline cation, the individual activated carbon (AC, negative) and MnO2/CNT (positive) electrodes are charged symmetrically up to a cell voltage of 1.8 V. Overall, due to the wide electrochemical stability window (∼2.0 V) and anti-freezing properties of ChNO$_{3}$-based aqueous electrolyte and the hierarchical design of the MnO$_{2}$/CNT composite, the asymmetric supercapacitor operates down to -40 °C and displays excellent energy and coulombic efficiency with no loss of performance after several thousand cycles. This work provides a new possibility on the low temperature application of high voltage supercapacitors

Probing the Effect of Titanium Substitution on the Sodium Storage in Na₃Ni₂BiO₆ Honeycomb-Type Structure

Na$_{3}$Ni$_{2}$BiO$_{6}$ with Honeycomb structure suffers from poor cycle stability when applied as cathode material for sodium-ion batteries. Herein, the strategy to improve the stability is to substitute Ni and Bi with inactive Ti. Monoclinic Na$_{3}$Ni$_{2-x}$Bi$_{1-y}$Ti$_{x+y}$O$_{6}$ powders with different Ti content were successfully synthesized via sol gel method, and 0.3 mol of Ti was determined as a maximum concentration to obtain a phase-pure compound. A solid-solution in the system of O3-NaNi$_{0.5}$Ti$_{0.5}$O$_{2}$ and O3-Na$_{3}$Ni$_{2}$BiO$_{6}$ is obtained when this critical concentration is not exceeded. The capacity of the first desodiation process at 0.1 C of Na$_{3}$Ni$_{2}$BiO$_{6}$ (~93 mAh g$^{-1}$) decreases with the increasing Ti concentration to ~77 mAh g$^{-1}$ for Na$_{3}$Ni$_{2}$Bi$_{0.9}$Ti$_{0.1}$O$_{6}$ and to ~82 mAh g$^{-1}$ for Na$_{3}$Ni$_{Zahl0.9}$Bi$_{0.8}$Ti$_{0.3}$O$_{6}$, respectively. After 100 cycles at 1 C, a better electrochemical kinetics is obtained for the Ti-containing structures, where a fast diffusion effect of Na$^{+}$-ions is more pronounced. As a result of in operando synchrotron radiation diffraction, during the first sodiation (O1-P3-O’3-O3) the O’3 phase, which is formed in the Na$_{3}$Ni$_{2}$BiO$_{6}$ is fully or partly replaced by P’3 phase in the Ti substituted compounds. This leads to an improvement in the kinetics of the electrochemical process. The pathway through prismatic sites of Na$^{+}$-ions in the P’3 phase seems to be more favourable than through octahedral sites of O’3 phase. Additionally, at high potential, a partial suppression of the reversible phase transition P3-O1-P3 is revealed

Electrochemical study on nickel aluminum layered double hydroxides as high-performance electrode material for lithium-ion batteries based on sodium alginate binder

Nickel aluminum layered double hydroxide (NiAl LDH) with nitrate in its interlayer is investigated as a negative electrode material for lithium-ion batteries (LIBs). The effect of the potential range (i.e., 0.01–3.0 V and 0.4–3.0 V vs. Li+/Li) and of the binder on the performance of the material is investigated in 1 M LiPF6 in EC/DMC vs. Li. The NiAl LDH electrode based on sodium alginate (SA) binder shows a high initial discharge specific capacity of 2586 mAh g−1 at 0.05 A g−1 and good stability in the potential range of 0.01–3.0 V vs. Li+/Li, which is better than what obtained with a polyvinylidene difluoride (PVDF)-based electrode. The NiAl LDH electrode with SA binder shows, after 400 cycles at 0.5 A g−1, a cycling retention of 42.2% with a capacity of 697 mAh g−1 and at a high current density of 1.0 A g−1 shows a retention of 27.6% with a capacity of 388 mAh g−1 over 1400 cycles. In the same conditions, the PVDF-based electrode retains only 15.6% with a capacity of 182 mAh g−1 and 8.5% with a capacity of 121 mAh g−1, respectively. Ex situ X-ray photoelectron spectroscopy (XPS) and ex situ X-ray absorption spectroscopy (XAS) reveal a conversion reaction mechanism during Li+ insertion into the NiAl LDH material. X-ray diffraction (XRD) and XPS have been combined with the electrochemical study to understand the effect of different cutoff potentials on the Li-ion storage mechanism