The properties of high theoretical capacity, low cost, and large potential of metallic sodium (Na) has strongly promoted the development of rechargeable sodium‐based batteries. However, the issues of ...infinite volume variation, unstable solid electrolyte interphase (SEI), and dendritic sodium causes a rapid decline in performance and notorious safety hazards. Herein, a highly reversible encapsulation‐based sodium storage by designing a functional hollow carbon nanotube with Zn single atom sites embedded in the carbon shell (ZnSA‐HCNT) is achieved. The appropriate tube space can encapsulate bulk sodium inside; the inner enriched ZnSA sites provide abundant sodiophilic sites, which can evidently reduce the nucleation barrier of Na deposition. Moreover, the carbon shell derived from ZIF‐8 provides geometric constraints and excellent ion/electron transport channels for the rapid transfer of Na+ due to its pore‐rich shell, which can be revealed by in situ transmission electron microscopy (TEM). As expected, Na@ZnSA‐HCNT anodes present steady long‐term performance in symmetrical battery (>900 h at 10 mA cm−2). Moreover, superior electrochemical performance of Na@ZnSA‐HCNT||PB full cells can be delivered. This work develops a new strategy based on carbon nanotube encapsulation of metallic sodium, which improves the safety and cycling performance of sodium metal anode.
Designing a functional encapsulation‐based sodium storage void with abundant pore structure and enriched Zn single atom sites in the inner wall is presented here. Zn single atoms provide abundant selective sodiophilic nucleation sites. Due to the rich pore structure, ZIF‐derived carbon shells can provide geometric constraints and excellent ion/electron transport channels to maintain fast electron/ion contact, benefiting for encapsulating large amounts of metallic sodium.
The redox reactions occurring in the Li-S battery positive electrode conceal various and critical electrocatalytic processes, which strongly influence the performances of this electrochemical energy ...storage system. Here, we report the development of a single-dispersed molecular cluster catalyst composite comprising of a polyoxometalate framework (Co
(PW
O
)
) and multilayer reduced graphene oxide. Due to the interfacial charge transfer and exposure of unsaturated cobalt sites, the composite demonstrates efficient polysulfides adsorption and reduced activation energy for polysulfides conversion, thus serving as a bifunctional electrocatalyst. When tested in full Li-S coin cell configuration, the composite allows for a long-term Li-S battery cycling with a capacity fading of 0.015% per cycle after 1000 cycles at 2 C (i.e., 3.36 A g
). An areal capacity of 4.55 mAh cm
is also achieved with a sulfur loading of 5.6 mg cm
and E/S ratio of 4.5 μL mg
. Moreover, Li-S single-electrode pouch cells tested with the bifunctional electrocatalyst demonstrate a specific capacity of about 800 mAh g
at a sulfur loading of 3.6 mg cm
for 100 cycles at 0.2 C (i.e., 336 mA g
) with E/S ratio of 5 μL mg
.
Polyoxometalates (POMs) are a series of molecular metal oxide clusters, which span the two domains of solutes and solid metal oxides. The unique characters of POMs in structure, geometry, and ...adjustable redox properties have attracted widespread attention in functional material synthesis, catalysis, electronic devices, and electrochemical energy storage and conversion. This review is focused on the links between the intrinsic charge carrier behaviors of POMs from a chemistry‐oriented view and their recent ground‐breaking developments in related areas. First, the advantageous charge transfer behaviors of POMs in molecular‐level electronic devices are summarized. Solar‐driven, thermal‐driven, and electrochemical‐driven charge carrier behaviors of POMs in energy generation, conversion and storage systems are also discussed. Finally, present challenges and fundamental insights are discussed as to the advanced design of functional systems based upon POM building blocks for their possible emerging application areas.
The links between the intrinsic charge‐carrier behaviors of polyoxometalates (POMs) from a chemistry‐oriented view are discussed and their recent ground‐breaking developments in related areas, including molecular‐level electronic devices, solar‐driven, thermally driven, and electrochemically driven energy generation, conversion, and storage systems are reviewed. Finally, present challenges and the fundamental insights for advanced design and self‐assembly of POM building blocks are also discussed.
Dendrite growth of alkali metal anodes limited their lifetime for charge/discharge cycling. Here, we report near-perfect anodes of lithium, sodium, and potassium metals achieved by electrochemical ...polishing, which removes microscopic defects and creates ultra-smooth ultra-thin solid-electrolyte interphase layers at metal surfaces for providing a homogeneous environment. Precise characterizations by AFM force probing with corroborative in-depth XPS profile analysis reveal that the ultra-smooth ultra-thin solid-electrolyte interphase can be designed to have alternating inorganic-rich and organic-rich/mixed multi-layered structure, which offers mechanical property of coupled rigidity and elasticity. The polished metal anodes exhibit significantly enhanced cycling stability, specifically the lithium anodes can cycle for over 200 times at a real current density of 2 mA cm
with 100% depth of discharge. Our work illustrates that an ultra-smooth ultra-thin solid-electrolyte interphase may be robust enough to suppress dendrite growth and thus serve as an initial layer for further improved protection of alkali metal anodes.
Sodium metal anodes are poor due to the reversibility of Na plating/stripping, which hinders their practical applications. A strategy to form a sodiophilic Au–Na alloy interphase on a Cu current ...collector, involving a sputtered Au thin layer, is shown to enable efficient Na plating/stripping for a certain period of time. Herein, electrochemical behaviors of Na plating on different substrates are explored, and it is revealed that the sodiophilic interphase can be achieved universally by in situ formation of M–Na (M = Au, Sn, and Sb) alloys during Na plating prior to Na bulk deposition in the initial cycle. Moreover, it is found that repetitive alloying–dealloying leads to falling‐off of thin film sodiophilic materials and thus limits the lifespan of efficient Na cycling. Therefore, an approach is further developed by employing particles of sodiophilic materials combined with the control over the cutoff potential, which significantly improves the stability of Na plating/stripping process. Especially, the low‐cost Cu@Sn‐NPs and Cu@Sb‐MPs composite current collectors allow Na plating and stripping to cycle for 2000 and 1700 times with the average efficiency of 99.9% at 2 mA cm−2.
Stable Na plating/stripping electrochemical behaviors are achieved by using the in situ formed sodiophilic sodium‐metal (metal = Au, Sn, Sb) alloy interphase. By simultaneous control over the stripping cut‐off potential and employment of anchored metal particles, Na plating/stripping cycling is extended to 2000 times at 2 mA cm−2 with an average Coulombic efficiency of 99.9% on the sodium‐metal alloy‐based interphase.
The rechargeable lithium-sulfur battery is regarded as a promising option for electrochemical energy storage systems owing to its high energy density, low cost and environmental friendliness. Further ...development of the Li-S battery, however, is still impeded by capacity decay and kinetic sluggishness caused by the polysulfide shuttle and electrode/electrolyte interface issues. Herein, a new type of metal-organic-framework-derived sulfur host containing cobalt and N-doped graphitic carbon (Co-N-GC) was synthesized and reported, in which the catalyzing for S redox, entrapping of polysulfides and an ideal electronic matrix were successfully achieved synchronously, leading to a significant improvement in the Li-S performance. The large surface area and uniform dispersion of cobalt nanoparticles within the N-doped graphitic carbon matrix contributed to a distinct enhancement in the specific capacity, rate performance and cycle stability for Li-S batteries. As a result of this multi-functional arrangement, cathodes with a high sulfur loading of 70 wt% could operate at 1C for over 500 cycles with nearly 100% coulombic efficiency and exhibited an outstanding high-rate response of up to 5C, suggesting that the SatCo-N-GC electrode was markedly improved by the proposed strategy, demonstrating its great potential for use in low-cost and high-energy Li-S batteries.
The polyoxovanadate cluster Li7V15O36(CO3) is shown to be an active cathode material in Li‐ion batteries, delivering a capacity of 250 mA h g−1 at 50 mA g−1 and 140 mA h g−1 at 10 A g−1. Li‐ion ...diffusion is rapid in this material and gives rise to an impressive maximum power density output of 25.7 kW kg−1 (55 kW L−1).
We present strategies to tune the redox properties of polyoxometalate clusters to enhance the electron‐coupled proton‐buffer‐mediated water splitting process, in which the evolution of hydrogen and ...oxygen can occur in different forms and is separated in time and space. By substituting the heteroatom template in the Keggin‐type polyoxometalate cluster, H6ZnW12O40, it is possible to double the number of electrons and protonation in the redox reactions (from two to four). This increase can be achieved with better matching of the energy levels as indicated by the redox potentials, compared to the ones of well‐studied H3PW12O40 and H4SiW12O40. This means that H6ZnW12O40 can act as a high‐performance redox mediator in an electrolytic cell for the on‐demand generation of hydrogen with a high decoupling efficiency of 95.5 % and an electrochemical energy efficiency of 83.3 %. Furthermore, the H6ZnW12O40 cluster also exhibits an excellent cycling behaviour and redox reversibility with almost 100 % H2‐mediated capacity retention during 200 cycles and a high coulombic efficiency >92 % each cycle at 30 mA cm−2.
The molecular structure of keggin‐type tungsten polyoxometalates (POMs) were tuned with different heteroatoms to modify their redox properties. Compared to the two electrons of well‐studied H3PW12O40 and H4SiW12O40, H6ZnW12O40 exhibits double reversible electrons with protonation in the redox reactions and the more desirable redox potentials, which enhance its ECPB performance (see scheme).
Sodium metal anodes combine low redox potential (−2.71 V versus SHE) and high theoretical capacity (1165 mAh g−1), becoming a promising anode material for sodium‐ion batteries. Due to the infinite ...volume change, unstable SEI films, and Na dendrite growth, it is arduous to achieve a long lifespan. Herein, an oxygen‐doped carbon foam (OCF) derived from starch is reported. Heteroatom doping can significantly reduce the nucleation resistance of sodium metal; combined with its rich pore structure and large specific surface area, OCF provides abundant nucleation sites to effectively guide the nucleation and subsequent growth of sodium metal, and the nature of this foam can accommodate the deposited sodium. Furthermore, a more uniform, robust, and stable SEI layer is observed on the surface of OCF electrode, so it can maintain ultra‐high reversibility and excellent integrity for a long time without dendritic growth. As a result, when the current density is 10 mA cm−2, the electrode can maintain stable 2000 cycles and the coulombic efficiency can reach to 99.83%. Na@OCF||Na3V2(PO4)3 full cell also has extremely high capacity retention of about 97.53% over 150 cycles. These results provide a simple but effective method for achieving the safety and commercialization of sodium metal anode.
An O‐doped carbon foam with a sodiophilic surface is constructed and applied to the sodium metal anode. The excellent sodiophilic property, abundant porous structure, and large specific surface make the material stable during multiple plating/stripping processes, and no sodium dendrites are formed. Consequently, the sodium metal battery exhibits excellent electrochemical performance.
High utilization and loading of sulfur in cathodes holds the key in the realization of Li–S batteries. We here synthesized a Co4N mesoporous sphere, which was made up of nanosheets, via an easy and ...convenient method. This material presents high affinity, speedy trapping, and absorbing capacity for polysulfides and acts as a bifunctional catalysis for sulfur redox processes; therefore it is an ideal matrix for S active material. With such a mesoporous sphere used as a sulfur host in Li–S batteries, extraordinary electrochemistry performance has been achieved. With a sulfur content of 72.3 wt % in the composite, the Co4N@S delivered a high specific discharge capacity of 1659 mAh g–1 at 0.1 C, almost reaching its theoretic capacity. Also, the battery exhibited a large reversible capacity of about 1100 mAh g–1 at 0.5 C and 1000 mAh g–1 at 1 C after 100 cycles. At a high rate of 2 C and 5 C, after 300 cycles, the discharge capacity finally stabilized at 805 and 585 mAh g–1. Even at a 94.88% sulfur content, the cathode can still deliver an extremely high specific discharge capacity of 1259 mAh g–1 with good cycle performance.
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