Among the aqueous rechargeable batteries, Zn 2+ -based batteries exhibit a series of unique attributes for large-scale energy storage: (i) feasibility of using low-cost Zn metal anode with a high theoretical specific capacity of 819 mA h g −1 ; (ii) replacement of the traditional alkaline electrolytes by mild neutral electrolytes, mitigating the environmental disruption and recycling costs; and (iii) low redox potential of Zn/Zn 2+ (−0.76 V vs standard hydrogen electrode) and two-electron transfer mechanism during cycling responsible for the high energy density. [6,22,23] However, the zinc system also has long-standing challenges, such as the unstable cathode and anode structures in the aqueous environment. On the cathode side, the cycling stability is related to how zinc ions and the electrolyte react with the cathode materials, which is much more complex as compared to the lithium-ion systems. An initial attempt on the hexacyanoferrate system delivered a limited capacity (≈60 mA h g −1 ), although a high operation voltage of ≈1.7 V was achieved. [23][24][25][26][27][28] Recently, Pan et al. demonstrated that the manganese oxide cathode goes through a chemical conversion reaction with the zinc species and H 2 O rather than the simple intercalation process, delivering a high capacity of ≈285 mA h g −1 and an operating voltage of ≈1.44 V. [29] Nazar's group developed a Zn 0.25 V 2 O 5 ·nH 2 O cathode material, which displayed a specific energy of ≈250 Wh kg −1 (based on cathode) and a high capacity of 220 mA h g −1 at 15 C (1 C = 300 mA g −1 ). [30] During cycling, the structural water in Zn 0.25 V 2 O 5 ·nH 2 O was revealed to exchange with Zn 2+ reversibly, thus resulting in good kinetics and rate performance. Furthermore, some other studies have also suggested the importance of H 2 O in metal ion intercalation. [23,31] During cycling, the solvating H 2 O works as a charge shield for the metal ions (Al 3+ , Mg 2+ , Li + , etc.), reducing their effective charges and hence their interactions with the host frameworks. [32,33] This strategy has been investigated to enhance the capacity and rate capability of Li + , Na + , and Mg 2+ batteries. [34][35][36][37][38][39] In this paper, we present a systematic and detailed study of the role of H 2 O in bilayer V 2 O 5 ·nH 2 O (n ≥ 1) as a prototype cathode material for zinc batteries. By coupling the electrochemical measurements, thermogravimetric/differential BatteriesLarge-scale energy storage systems are critical for the integration of renewable energy and electric energy infrastructures. [1][2][3] Among numerous candidates, lithium-ion batteries with organic electrolytes are one of the most attractive options due to their high energy density [4][5][6][7][8][9][10] and mature markets. [11,12] However, for grid scale energy storage, the cost of lithium-ion batteries is still too high, [13,14] and the use of the flammable organic electrolyte in large format batteries poses a severe safety and environmental concern. [15] As an alternative, low-cost aqueous batteries wi...

Herein, we report the synthesis of multiscale nanostructured p-type (Bi,Sb)(2)Te(3) bulk materials by melt-spinning single elements of Bi, Sb, and Te followed by a spark plasma sintering process. The samples that were most optimized with the resulting composition (Bi(0.48)Sb(1.52)Te(3)) and specific nanostructures showed an increase of approximately 50% or more in the figure of merit, ZT, over that of the commercial bulk material between 280 and 475 K, making it suitable for commercial applications related to both power generation and refrigeration. The results of high-resolution electron microscopy and small angle and inelastic neutron scattering along with corresponding thermoelectric property measurements corroborate that the 10-20 nm nanocrystalline domains with coherent boundaries are the key constituent that accounts for the resulting exceptionally low lattice thermal conductivity and significant improvement of ZT.

Resonant levels are promising for high-performance single-phase thermoelectric materials. Recently, phase-change materials have attracted much attention for energy conversion applications. As the energetic position of resonant levels could be temperature dependent, searching for dopants in phase-change materials, which can introduce resonant levels in both low and high temperature phases, remains challenging. In this study, possible distortions of the electronic density of states due to group IIIA elements (Ga, In, Tl) in GeTe are theoretically investigated. Resonant levels induced by indium dopants in both rhombohedral and cubic phase GeTe have been demonstrated. The experimental Seebeck coefficients of In x Ge 1 − x Te exhibit a large enhancement compared with those observed for other prior dopants. Indium dopants reduce the defect concentrations in GeTe, and thus, they lower the carrier concentrations and suppress the electronic component of the total thermal conductivity. The enhanced Seebeck coefficient, together with the suppressed thermal conductivity, leads to a reasonably high ZT of 1.3 at a temperature near 355°C in In 0.02 Ge 0.98 Te. The corresponding average ZT is enhanced by~70% across the entire temperature range of the rhombohedral and cubic phases. These observations indicate that indium-doped GeTe is a promising base material for achieving an even higher thermoelectric performance.

Rechargeable aqueous Zn-ion batteries (ZIBs) are very promising for large-scale grid energy storage applications owing to their low cost, environmentally benign constituents, excellent safety, and relatively high energy density. 1, 2 Their usage, however, is largely hampered by the fast capacity fade. The cycle stability seems to be highly rate-dependent, 3 which poses an additional challenge, but can also play a pivotal role in uncovering the reaction mechanisms. The complexity of the reactions has resulted in long-standing ambiguities of the chemical pathways of Zn/MnO2 system, and has led to many controversies with regard to their nature. In this report, we present a combined experimental and theoretical study of Zn/ MnO2 cells. We found that both H + /Zn 2+ intercalation and conversion reactions occur at different voltages, and that the rapid capacity fading can clearly be ascribed to the rate-limiting and irreversible conversion reactions at a lower voltage. By avoiding the irreversible conversion reactions at ~ 1.26 V, we successfully demonstrate ultra-high power and long-life Zn/MnO2 cells which, after 1000 cycles, maintain an energy density of ~ 231 Wh kg-1 and ~ 105 Wh kg-1 at a power density of ~ 4 kW kg-1 (9C, ~ 3.1 A g-1) and ~ 15 kW kg-1 (30C, ~ 10.3 A g-1), respectively. The excellent cycle stability and power capability are superior to most reported ZIBs or even some lithium-ion batteries. The results establish accurate electrochemical reaction mechanisms and kinetics for Zn/MnO2, and identify the interplay of the voltage window and rate as the determining factors for achieving excellent cycle life. Broader Context The increasing interest and importance in large-scale grid storage technology are attributed to multiple factors, including managing peak demands, improving the grid reliability, integrating most sustainable energy sources such as solar radiation, wind, wave power, geothermal energy, etc., and further powering the energy infrastructures. Rechargeable aqueous Zn-ion batteries (ZIBs) with mild electrolytes have the advantages of low cost materials (Zn/ MnO2), manufacturing (air-and water-inert Zn anode), and recycling (mild electrolytes); relatively high energy density; and excellent safety, making them prospective candidates for large-scale grid storage. Their low cyclability, however, has remained a grand challenge, hindering the widespread applications of these attractive ZIBs. A prerequisite for improving the cycle life and electrochemical performance of Zn/MnO2 batteries is to accurately determine the reaction mechanisms, especially under different rates, which poses a considerable challenge. In our combined experimental and computational study, a concomitant intercalation and conversion reactions of H + /Zn 2+ occurring at different voltages in the Zn/MnO2 system is established. The rapid capacity fading is unambiguously ascribed to the rate-limiting and irreversible conversion reactions at a lower voltage. By mitigating or avoiding the irreversible conversion reactions at the lower ...

The interfacial impedances existing on electrode/solid electrolyte interfaces dictate the transport of Li-ions during the electrochemical processes.

No abstract

Layered oxide cathodes with a high Ni content of >0.6 are promising for high-energy-density lithium-ion batteries. However, parasitic electrolyte oxidation of the charged cathode and mechanical degradation arising from phase transitions significantly deteriorate the cell performance and cycle life as the Ni content increases. We demonstrate here a significantly prolonged cycle life with superior cell performance by substituting a small-dose of Al (2 mol %) for Ni in LiNi0.92Co0.06Al0.02O2; the capacity retention after operating a full cell fabricated with graphite anode for 1000 cycles increases from 47% to 83% on going from the Al-free LiNi0.94Co0.06O2 to the Al-doped LiNi0.92Co0.06Al0.02O2 cathode. Through in situ X-ray diffraction, we provide the operando evidence that the Al-doping tunes the H2–H3 phase transition process from a two-phase reaction to a quasi-monophase reaction, minimizing the mechanical degradation. Furthermore, secondary-ion mass spectrometry reveals considerably suppressed transition-metal dissolution with Al-doping, effectively preventing sustained parasitic reactions and active Li trapping due to chemical crossover on graphite anodes. This work offers a viable approach for adopting high-Ni cathodes in lithium-ion batteries.

The filling fraction limit (FFL) of skutterudites, that is, the complex balance of formation enthalpies among different species, is an intricate but crucial parameter for achieving high thermoelectric performance. In this work, we synthesized a series of Yb x Co 4 Sb 12 samples with x = 0.2-0.6 and systemically studied the FFL of Yb, which is still debated even though this system has been extensively investigated for decades. Our combined experimental efforts of X-ray diffraction, microstructural and quantitative compositional analyses clearly reveal a Yb FFL of~0.29 in CoSb 3 , which is consistent with previous theoretical calculations. The excess Yb in samples with x40.35 mainly form metallic YbSb 2 precipitates, significantly raising the Fermi level and thus increasing the electrical conductivity and decreasing the Seebeck coefficient. This result is further corroborated by the numerical calculations based on the Bergman's composite theory, which accurately reproduces the transport properties of the x40.35 samples based on nominal Yb 0.35 Co 4 Sb 12 and YbSb 2 composites. A maximum ZT of 1.5 at 850 K is achieved for Yb 0.3 Co 4 Sb 12 , which is the highest value for a single-element-filled CoSb 3 . The high ZT originates from the high-power factor (in excess of 50 μW cm-K − 2 ) and low lattice thermal conductivity (well below 1.0 W m-K − 1 ). More importantly, the large average ZTs, for example,~1.05 for 300-850 K and~1.27 for 500-850 K, are comparable to the best values for n-type skutterudites. The high thermoelectric and thermomechanical performances and the relatively low air and moisture sensitivities of Yb make Yb-filled CoSb 3 , a promising candidate for large-scale power generation applications.