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1.
Adv Mater ; : e2107353, 2021 Nov 04.
Artigo em Inglês | MEDLINE | ID: mdl-34738266

RESUMO

The increasing demand for energy storage is calling for improvements in cathode performance. In traditional layered cathodes, the higher energy of the metal 3d over the O 2p orbital results in one-band cationic redox; capacity solely from cations cannot meet the needs for higher energy density. Emerging anionic redox chemistry is promising to access higher capacity. In recent studies, the low-lying O nonbonding 2p orbital was designed to activate one-band oxygen redox, but they are still accompanied by reversibility problems like oxygen loss, irreversible cation migration, and voltage decay. Herein, by regulating the metal-ligand energy level, both extra capacities provided by anionic redox and highly reversible anionic redox process are realized in NaCr1- y Vy S2 system. The simultaneous cationic and anionic redox of Cr/V and S is observed by in situ X-ray absorption near edge structure (XANES). Under high d-p hybridization, the strong covalent interaction stabilizes the holes on the anions, prevents irreversible dimerization and cation migration, and restrains voltage hysteresis and voltage decay. The work provides a fundamental understanding of highly reversible anionic redox in layered compounds, and demonstrates the feasibility of anionic redox chemistry based on hybridized bands with d-p covalence.

2.
Chem Commun (Camb) ; 57(80): 10371-10374, 2021 Oct 07.
Artigo em Inglês | MEDLINE | ID: mdl-34541598

RESUMO

A transformative concept of solid electrochemical corrosion has been put forward, in which solid-state electrolyte LiPON has been applied to replace the liquid one to prelithiate graphite with Li-metal. Thus, high prelithiation efficiency and low polarization of the treated anode can be obtained, with a unique mosaic structure left at the surface.

3.
Adv Mater ; 33(13): e2008194, 2021 Apr.
Artigo em Inglês | MEDLINE | ID: mdl-33645858

RESUMO

Oxygen-redox of layer-structured metal-oxide cathodes has drawn great attention as an effective approach to break through the bottleneck of their capacity limit. However, reversible oxygen-redox can only be obtained in the high-voltage region (usually over 3.5 V) in current metal-oxide cathodes. Here, we realize reversible oxygen-redox in a wide voltage range of 1.5-4.5 V in a P2-layered Na0.7 Mg0.2 [Fe0.2 Mn0.6 □0.2 ]O2 cathode material, where intrinsic vacancies are located in transition-metal (TM) sites and Mg-ions are located in Na sites. Mg-ions in the Na layer serve as "pillars" to stabilize the layered structure during electrochemical cycling, especially in the high-voltage region. Intrinsic vacancies in the TM layer create the local configurations of "□-O-□", "Na-O-□" and "Mg-O-□" to trigger oxygen-redox in the whole voltage range of charge-discharge. Time-resolved techniques demonstrate that the P2 phase is well maintained in a wide potential window range of 1.5-4.5 V even at 10 C. It is revealed that charge compensation from Mn- and O-ions contributes to the whole voltage range of 1.5-4.5 V, while the redox of Fe-ions only contributes to the high-voltage region of 3.0-4.5 V. The orphaned electrons in the nonbonding 2p orbitals of O that point toward TM-vacancy sites are responsible for reversible oxygen-redox, and Mg-ions in Na sites suppress oxygen release effectively.

4.
Chem Commun (Camb) ; 57(23): 2867-2870, 2021 Mar 18.
Artigo em Inglês | MEDLINE | ID: mdl-33629086

RESUMO

P3-Na0.65Mn0.5Al0.5O2 (NMAO) has been synthesized and studied as a cathode for sodium batteries, and shows anionic redox reaction (ARR) and exhibits a first charging capacity of ∼110 mA h g-1. The electrochemical mechanism of NMAO was comprehensively investigated by X-ray absorption spectroscopy (XAS), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and density functional theory (DFT) calculations. The reversible oxygen redox behaviour is triggered by Al3+ through oxygen quasi non-bonding states generated by the relatively ionic interaction of Al and O. Furthermore, the presence of Al3+ can suppress oxygen loss in ARR. This work provides new insights into the design and mechanism of anionic redox active cathode materials.

5.
Nat Commun ; 10(1): 4458, 2019 10 01.
Artigo em Inglês | MEDLINE | ID: mdl-31575867

RESUMO

The use of anion redox reactions is gaining interest for increasing rechargeable capacities in alkaline ion batteries. Although anion redox coupling of S2- and (S2)2- through dimerization of S-S in sulfides have been studied and reported, an anion redox process through electron hole formation has not been investigated to the best of our knowledge. Here, we report an O3-NaCr2/3Ti1/3S2 cathode that delivers a high reversible capacity of ~186 mAh g-1 (0.95 Na) based on the cation and anion redox process. Various charge compensation mechanisms of the sulfur anionic redox process in layered NaCr2/3Ti1/3S2, which occur through the formation of disulfide-like species, the precipitation of elemental sulfur, S-S dimerization, and especially through the formation of electron holes, are investigated. Direct structural evidence for formation of electron holes and (S2)n- species with shortened S-S distances is obtained. These results provide valuable information for the development of materials based on the anionic redox reaction.

6.
J Am Chem Soc ; 141(2): 840-848, 2019 Jan 16.
Artigo em Inglês | MEDLINE | ID: mdl-30562030

RESUMO

Most P2-type layered oxides suffer from multiple voltage plateaus, due to Na+/vacancy-order superstructures caused by strong interplay between Na-Na electrostatic interactions and charge ordering in the transition metal layers. Here, Mg ions are successfully introduced into Na sites in addition to the conventional transition metal sites in P2-type Na0.7[Mn0.6Ni0.4]O2 as new cathode materials for sodium-ion batteries. Mg ions in the Na layer serve as "pillars" to stabilize the layered structure, especially for high-voltage charging, meanwhile Mg ions in the transition metal layer can destroy charge ordering. More importantly, Mg ion occupation in both sodium and transition metal layers will be able to create "Na-O-Mg" and "Mg-O-Mg" configurations in layered structures, resulting in ionic O 2p character, which allocates these O 2p states on top of those interacting with transition metals in the O-valence band, thus promoting reversible oxygen redox. This innovative design contributes smooth voltage profiles and high structural stability. Na0.7Mg0.05[Mn0.6Ni0.2Mg0.15]O2 exhibits superior electrochemical performance, especially good capacity retention at high current rate under a high cutoff voltage (4.2 V). A new P2 phase is formed after charge, rather than an O2 phase for the unsubstituted material. Besides, multiple intermediate phases are observed during high-rate charging. Na-ion transport kinetics are mainly affected by elemental-related redox couples and structural reorganization. These findings will open new opportunities for designing and optimizing layer-structured cathodes for sodium-ion batteries.

7.
ACS Omega ; 3(7): 7648-7654, 2018 Jul 31.
Artigo em Inglês | MEDLINE | ID: mdl-31458915

RESUMO

A Prussian blue LiFeFe(CN)6 thin-film cathode is fabricated by a nonvacuum coating technology without post-annealing process. The thin film of the solid electrolyte lithium phosphorus oxynitride (LiPON) is deposited onto the cathode by using radio-frequency magnetron sputtering. Then, the lithium metal anode is deposited on the LiPON film by the thermal evaporation method to fabricate the all-solid-state LiFeFe(CN)6/LiPON/Li battery with a thickness of 16 µm and a size of ∼10 cm2. Electrochemical properties of LiFeFe(CN)6/LiPON/Li battery are first investigated at various temperatures from -30 to 80 °C. Our results demonstrated that the all-solid-state LiFeFe(CN)6/LiPON/Li battery exhibits a discharge capacity of 82.5 mA h/g for the third cycle at 60 °C and shows stable cyclic performance within 200 cycles. These results provide the feasibility to assemble an all-solid-state lithium-ion battery by combining nonvacuum and vacuum techniques through an environmentally friendly process at low temperature.

8.
Adv Sci (Weinh) ; 4(11): 1700219, 2017 11.
Artigo em Inglês | MEDLINE | ID: mdl-29201619

RESUMO

Developing sodium-ion batteries for large-scale energy storage applications is facing big challenges of the lack of high-performance cathode materials. Here, a series of new cathode materials Na0.66Co x Mn0.66-x Ti0.34O2 for sodium-ion batteries are designed and synthesized aiming to reduce transition metal-ion ordering, charge ordering, as well as Na+ and vacancy ordering. An interesting structure change of Na0.66Co x Mn0.66-x Ti0.34O2 from orthorhombic to hexagonal is revealed when Co content increases from x = 0 to 0.33. In particular, Na0.66Co0.22Mn0.44Ti0.34O2 with a P2-type layered structure delivers a reversible capacity of 120 mAh g-1 at 0.1 C. When the current density increases to 10 C, a reversible capacity of 63.2 mAh g-1 can still be obtained, indicating a promising rate capability. The low valence Co2+ substitution results in the formation of average Mn3.7+ valence state in Na0.66Co0.22Mn0.44Ti0.34O2, effectively suppressing the Mn3+-induced Jahn-Teller distortion, and in turn stabilizing the layered structure. X-ray absorption spectroscopy results suggest that the charge compensation of Na0.66Co0.22Mn0.44Ti0.34O2 during charge/discharge is contributed by Co2.2+/Co3+ and Mn3.3+/Mn4+ redox couples. This is the first time that the highly reversible Co2+/Co3+ redox couple is observed in P2-layered cathodes for sodium-ion batteries. This finding may open new approaches to design advanced intercalation-type cathode materials.

9.
Nat Commun ; 8(1): 566, 2017 09 18.
Artigo em Inglês | MEDLINE | ID: mdl-28924149

RESUMO

The intercalation compounds with various electrochemically active or inactive elements in the layered structure have been the subject of increasing interest due to their high capacities, good reversibility, simple structures, and ease of synthesis. However, their reversible intercalation/deintercalation redox chemistries in previous compounds involve a single cationic redox reaction or a cumulative cationic and anionic redox reaction. Here we report an anionic redox chemistry and structural stabilization of layered sodium chromium sulfide. It was discovered that the sulfur in sodium chromium sulfide is electrochemically active, undergoing oxidation/reduction rather than chromium. Significantly, sodium ions can successfully move out and into without changing its lattice parameter c, which is explained in terms of the occurrence of chromium/sodium vacancy antisite during desodiation and sodiation processes. Our present work not only enriches the electrochemistry of layered intercalation compounds, but also extends the scope of investigation on high-capacity electrodes.The rational design of intercalation electrodes is largely confined to the optimization of redox chemistry of transition metals and oxygen. Here, the authors report the single anionic redox process in NaCrS2 where it is sulfur rather than chromium that works as the electrochemical active species.

10.
Chem Commun (Camb) ; 53(9): 1522-1525, 2017 Jan 26.
Artigo em Inglês | MEDLINE | ID: mdl-28093586

RESUMO

Heterogeneous catalysts with Co3O4 and liquid redox mediators were utilized for the morphological control of discharged products in SABs. With Co3O4 nanowires/C as air cathodes, the discharge product tended to be like nanoflakes. However, after the addition of ferrocene to the electrolyte, the discharge product tended to be like nanofilms and the cyclic performance can achieve 570 cycles.

11.
Inorg Chem ; 55(13): 6504-10, 2016 Jul 05.
Artigo em Inglês | MEDLINE | ID: mdl-27308962

RESUMO

A novel small-molecule compound of lithium iodine and 3-hydroxypropionitrile (HPN) has been successfully synthesized. Our combined experimental and theoretical studies indicated that LiIHPN is a Li-ion conductor, which is utterly different from the I(-)-anion conductor of LiI(HPN)2 reported previously. Solid-state lithium-air batteries based on LiIHPN as the electrolyte exhibit a reversible discharge capacity of more than 2100 mAh g(-1) with a cyclic performance over 10 cycles. Our findings provide a new way to design solid-state electrolytes toward high-performance lithium-air batteries.

12.
Chem Commun (Camb) ; 51(86): 15712-5, 2015 Nov 07.
Artigo em Inglês | MEDLINE | ID: mdl-26365902

RESUMO

A well-crystallized single-phase quinary layer transition metal oxide of NaNi1/4Co1/4Fe1/4Mn1/8Ti1/8O2 was successfully synthesized. It exhibited excellent cycle performance and high rate capability as a cathode material for sodium-ion batteries.

13.
Chem Commun (Camb) ; 51(52): 10486-9, 2015 Jul 04.
Artigo em Inglês | MEDLINE | ID: mdl-26030004

RESUMO

A CoS2/multi-walled carbon nanotube (MWCNT) nanocomposite was synthesized and its sodium storage performances in ether-based electrolyte and commonly used carbonate-based electrolyte were investigated for the first time. A high capacity of 568 mA h g(-1) after 100 cycles in ether-based electrolyte can be achieved.

14.
Sci Rep ; 5: 8810, 2015 Mar 06.
Artigo em Inglês | MEDLINE | ID: mdl-25744589

RESUMO

The key factors governing the single-phase or multi-phase structural change behaviors during the intercalation/deintercalation of guest ions have not been well studied and understood yet. Through systematic studies of orthorhombic Fe2(MoO4)3 electrode, two distinct guest ion occupation paths, namely discrete one for Li and pseudo-continuous one for Na, as well as their relationship with single-phase and two-phase modes for Na(+) and Li(+), respectively during the intercalation/deintercalation process have been demonstrated. For the first time, the direct atomic-scale observation of biphasic domains (discrete occupation) in partially lithiated Fe2(MoO4)3 and the one by one Na occupation (pseudo-continuous occupation) at 8d sites in partially sodiated Fe2(MoO4)3 are obtained during the discharge processes of Li/Fe2(MoO4)3 and Na/Fe2(MoO4)3 cells respectively. Our combined experimental and theoretical studies bring the new insights for the research and development of intercalation compounds as electrode materials for secondary batteries.

15.
Chem Commun (Camb) ; 51(12): 2324-7, 2015 Feb 11.
Artigo em Inglês | MEDLINE | ID: mdl-25562720

RESUMO

A Na-air battery with NaI dissolved in a typical organic electrolyte could run up to 150 cycles with a capacity limit of 1000 mA h g(-1). The low charge voltage plateau of 3.2 V vs. Na(+)/Na in a Na-air battery should mainly be attributed to the oxidation reaction of active iodine anions.

16.
J Am Chem Soc ; 136(23): 8153-6, 2014 Jun 11.
Artigo em Inglês | MEDLINE | ID: mdl-24863686

RESUMO

We report a robust synthesis of Ag@Au core-shell nanocubes by directly depositing Au atoms on the surfaces of Ag nanocubes as conformal, ultrathin shells. Our success relies on the introduction of a strong reducing agent to compete with and thereby block the galvanic replacement between Ag and HAuCl4. An ultrathin Au shell of 0.6 nm thick was able to protect the Ag in the core in an oxidative environment. Significantly, the core-shell nanocubes exhibited surface plasmonic properties essentially identical to those of the original Ag nanocubes, while the SERS activity showed a 5.4-fold further enhancement owing to an improvement in chemical enhancement. The combination of excellent SERS activity and chemical stability may enable a variety of new applications.


Assuntos
Ouro/química , Nanocompostos/química , Prata/química , Análise Espectral Raman , Cloretos/química , Técnicas Eletroquímicas , Compostos de Ouro/química , Microscopia Eletrônica de Transmissão , Nanotecnologia/instrumentação , Nanotecnologia/métodos , Oxirredução , Análise Espectral Raman/instrumentação , Análise Espectral Raman/métodos , Propriedades de Superfície
17.
ACS Appl Mater Interfaces ; 6(4): 2209-12, 2014 Feb 26.
Artigo em Inglês | MEDLINE | ID: mdl-24494989

RESUMO

Here we demonstrate for the first time that CFx cathodes show rechargeable capability in sodium ion batteries with an initial discharge capacity of 1061 mAh g(-1) and a reversible discharge capacity of 786 mAh g(-1). The highly reversible electrochemical reactivity of CFx with Na at room temperature indicates that the decomposition of NaF could be driven by carbon formed during the first discharge. The high reversible capacity made it become a promising cathode material for future rechargeable sodium batteries.

18.
ACS Appl Mater Interfaces ; 6(5): 3750-7, 2014 Mar 12.
Artigo em Inglês | MEDLINE | ID: mdl-24476231

RESUMO

We report a strategy to complement the galvanic replacement reaction between Ag nanocubes and HAuCl4 with co-reduction by ascorbic acid (AA) for the formation of Ag-Au hollow nanostructures with greatly enhanced SERS activity. Specifically, in the early stage of synthesis, the Ag nanocubes are sharpened at corners and edges because of the selective deposition of Au and Ag atoms at these sites. In the following steps, the pure Ag in the nanocubes is constantly converted into Ag(+) ions to generate voids owing to the galvanic reaction with HAuCl4, but these released Ag(+) ions are immediately reduced back to Ag atoms and are co-deposited with Au atoms onto the nanocube templates. We observe distinctive SERS properties for the Ag-Au hollow nanostructures at visible and near-infrared excitation wavelengths. When plasmon damping is eliminated by using an excitation wavelength of 785 nm, the SERS activity of the Ag-Au hollow nanostructures is 15- and 33-fold stronger than those of the original Ag nanocubes and the Ag-Au nanocages prepared by galvanic replacement without co-reduction, respectively. Additionally, Ag-Au hollow nanostructures embrace considerably improved stability in an oxidizing environment such as aqueous H2O2 solution. Collectively, our work suggests that the Ag-Au hollow nanostructures will find applications in SERS detection and imaging.


Assuntos
Ouro/química , Nanoestruturas/química , Prata/química , Análise Espectral Raman/instrumentação , Nanotecnologia/instrumentação , Tamanho da Partícula , Propriedades de Superfície
19.
Small ; 10(7): 1430-7, 2014 Apr 09.
Artigo em Inglês | MEDLINE | ID: mdl-24339345

RESUMO

We investigate the role of etching in the formation of Ag nanoplates with different morphologies. By examining the reduction of AgNO3 with poly(vinyl pyrrolidone) in an aqueous solution under a hydrothermal condition, we confirm that etching plays an essential role in promoting the growth of Ag triangular nanoplates with straight edges at the expense of multiple twinned particles via Ostwald ripening. Once all the multiple twinned particles are gone, etching will continue at the corners of nanoplates, leading to the formation of enneahedral nanoplates with curved edges. When the nanoplates with straight edges are transferred into ethanol and subjected to a solvothermal treatment, we obtain nanoplates with wavy edges and sharp corners due to etching on the edges. A comparison study indicates that, at the same particle concentration, Ag nanoplates with wavy edges embraces a SERS enhancement factor at least 6 and 13 times stronger than those with straight and curved edges, respectively. The results from finite difference time domain calculations support our experimental observation that the sharp features on nanoplates with wavy edges are the most active sites for SERS.

20.
Phys Chem Chem Phys ; 15(38): 15806-10, 2013 Oct 14.
Artigo em Inglês | MEDLINE | ID: mdl-23949447

RESUMO

A 3D NiCo2O4 nanowire array/carbon cloth (NCONW/CC) was employed as the cathode for Li-air batteries with a non-aqueous electrolyte. After its discharge, novel porous ball-like Li2O2 was found to be deposited on the tip of NiCo2O4 nanowires. The special structure of Li2O2 and active sites of catalysts are also discussed.

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