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1.
Nanoscale Horiz ; 2020 Mar 29.
Artigo em Inglês | MEDLINE | ID: mdl-32222748

RESUMO

Hard carbon materials have been recognized as a promising family of anode materials for potassium ion batteries (PIBs), but their practical application is severely hindered due to the inferior initial coulombic efficiency (ICE) and low capacity. Herein, we report our findings in simultaneously improved potassium storage capacity and ICE through the design of nano-size and porous structure and the appropriate selection of electrolytes. Benefiting from the high specific surface area, stable electrode|electrolyte interface, and fast potassium ion and electron transfer, the optimized electrode exhibits a high ICE of up to 68.2% and an outstanding reversible capacity of 232.6 mA h g-1 at 200 mA g-1. In particular, superior cycling stability of 165.2 mA h g-1 at 1000 mA g-1 and 129.7 mA h g-1 at 2000 mA g-1 can be retained after 1500 cycles, respectively. Quantitative analysis reveals that this optimized structure leads to an enhanced surface-controlled contribution, resulting in fast potassiation kinetics and electronic|ionic conductivities, which are regarded as essential features for potassium storage. Our findings in this work provide an efficient strategy to significantly improve potassium storage capacity while maintaining a high ICE for hard carbon electrodes.

2.
Proc Natl Acad Sci U S A ; 117(6): 2815-2823, 2020 Feb 11.
Artigo em Inglês | MEDLINE | ID: mdl-31996477

RESUMO

Existing lithium-ion battery technology is struggling to meet our increasing requirements for high energy density, long lifetime, and low-cost energy storage. Here, a hybrid electrode design is developed by a straightforward reengineering of commercial electrode materials, which has revolutionized the "rocking chair" mechanism by unlocking the role of anions in the electrolyte. Our proof-of-concept hybrid LiFePO4 (LFP)/graphite electrode works with a staged deintercalation/intercalation mechanism of Li+ cations and PF6 - anions in a broadened voltage range, which was thoroughly studied by ex situ X-ray diffraction, ex situ Raman spectroscopy, and operando neutron powder diffraction. Introducing graphite into the hybrid electrode accelerates its conductivity, facilitating the rapid extraction/insertion of Li+ from/into the LFP phase in 2.5 to 4.0 V. This charge/discharge process, in turn, triggers the in situ formation of the cathode/electrolyte interphase (CEI) layer, reinforcing the structural integrity of the whole electrode at high voltage. Consequently, this hybrid LFP/graphite-20% electrode displays a high capacity and long-term cycling stability over 3,500 cycles at 10 C, superior to LFP and graphite cathodes. Importantly, the broadened voltage range and high capacity of the hybrid electrode enhance its energy density, which is leveraged further in a full-cell configuration.

3.
ACS Nano ; 13(10): 11843-11852, 2019 Oct 22.
Artigo em Inglês | MEDLINE | ID: mdl-31545592

RESUMO

Vacancy engineering is a promising approach for optimizing the energy storage performance of transition metal dichalcogenides (TMDs) due to the unique properties of vacancies in manipulating the electronic structure and active sites. Nevertheless, achieving effective introduction of anion vacancies with adjustable vacancy concentration on a large scale is still a big challenge. Herein, MoS2(1-x)Se2x alloys with anion vacancies introduced in situ have been achieved by a simple alloying reaction, and the vacancy concentration has been optimized through adjusting the chemical composition. Experimental and density functional theory calculation results suggest that the anion vacancies in MoS2(1-x)Se2x alloys could enhance the electronic conductivity, induce more active sites, and alleviate structural variation in the alloys during the potassium storage process. When applied as potassium ion battery anodes, the most optimized vacancy-rich MoSSe alloy delivered high reversible capacities of 517.4 and 362.4 mAh g-1 at 100 and 1000 mA g-1, respectively. Moreover, a reversible capacity of 220.5 mAh g-1 could be maintained at 2000 mA g-1 after 1000 cycles. This work demonstrates a practical approach to modifying the electronic and defect properties of TMDs, providing an effective strategy for constructing advanced electrode materials for battery systems.

4.
ACS Nano ; 13(8): 9247-9258, 2019 Aug 27.
Artigo em Inglês | MEDLINE | ID: mdl-31334639

RESUMO

Phosphorus doping is an effective strategy to simultaneously improve the electronic conductivity and regulate the ionic diffusion kinetics of TiO2 being considered as anode materials for sodium ion batteries. However, efficient phosphorus doping at high concentration in well-crystallized TiO2 nanoparticles is still a big challenge. Herein, we propose a defect-assisted phosphorus doping strategy to selectively engineer the surface structure of TiO2 nanoparticles. The reduced TiO2-x shell layer that is rich in oxygen defects and Ti3+ species precisely triggered a high concentration of phosphorus doping (∼7.8 at. %), and consequently a TiO2@TiO2-x-P core@shell architecture was produced. Comprehensive characterizations and first-principle calculations proved that the surface-functionalized TiO2-x-P thin layer endowed the TiO2@TiO2-x-P with substantially enhanced electronic conductivity and accelerated Na ion transportation, resulting in great rate capability (167 mA h g-1 at 10 000 mA g-1) and stable cycling (99% after 5000 cycles at 10 A g-1). Combining in/ex situ X-ray diffraction with ex situ electron spin resonance clearly demonstrated the high reversibility and robust mechanical behavior of TiO2@TiO2-x-P upon long-term cycling. This work provides an interesting and effective strategy for precise heteroatoms doping to improve the electrochemical performance of nanoparticles.

5.
J Colloid Interface Sci ; 530: 127-136, 2018 Nov 15.
Artigo em Inglês | MEDLINE | ID: mdl-29966845

RESUMO

The performance of energy storage materials is substantially dependent on their nanostructures. Herein, Ni-1,3,5-benzenetricarboxylate metal-organic frameworks (Ni-BTC MOFs) with different morphologies are controllably synthesized using a facile solvothermal method by simply adjusting the solvent and their electrochemical performance as an anode material for lithium-ion batteries is thoroughly investigated. Among the synthesized Ni-BTC MOFs with different morphologies, a hierarchical mesoporous flower-like Ni-BTC MOF (Ni-BTCEtOH) assembled from two-dimensional nanosheets shows the best electrochemical properties including a high capacity of 1085 mA h g-1 at 100 mA g-1 (358 mA h g-1 at 5000 mA g-1), excellent cycling stability at 1000 mA g-1 for 1000 cycles, and great rate performance, which is superior to most of the reported MOF-based anode materials for lithium-ion batteries. The outstanding electrochemical performance of Ni-BTCEtOH is originated from its unique and stable hierarchical mesoporous morphology with a high specific surface area and improved electrical/ionic conductivity. Moreover, our study demonstrates that the charge-discharge mechanism of the Ni-BTCEtOH electrode involves the insertion/extraction of Li ions to/from the organic moieties in Ni-BTCEtOH during the charge-discharge process without the direct engagement of Ni2+. This work highlights that the nanostructure design is an effective strategy to obtain promising energy storage materials.

6.
Adv Mater ; 30(26): e1801013, 2018 Jun.
Artigo em Inglês | MEDLINE | ID: mdl-29744949

RESUMO

Structural design and modification are effective approaches to regulate the physicochemical properties of TiO2 , which play an important role in achieving advanced materials. Herein, a plasma-assisted method is reported to synthesize a surface-defect-rich and deep-cation-site-rich S doped rutile TiO2 (R-TiO2-x -S) as an advanced anode for the Na ion battery. An amorphous shell (≈3 nm) is induced by the Ar/H2 plasma, which brings about the subsequent high S doping concentration (≈4.68 at%) and deep doping depth. Experimental results and density functional theory calculations demonstrate greatly facilitated ion diffusion, improved electronic conductivity, and an increased mobility rate of holes for R-TiO2-x -S, which result in superior rate capability (264.8 and 128.5 mAh g-1 at 50 and 10 000 mA g-1 , respectively) and excellent cycling stability (almost 100% retention over 6500 cycles). Such improvements signify that plasma treatment offers an innovative and general approach toward designing advanced battery materials.

7.
ACS Appl Mater Interfaces ; 10(8): 7031-7042, 2018 Feb 28.
Artigo em Inglês | MEDLINE | ID: mdl-29338183

RESUMO

The incorporation of oxygen vacancies in anatase TiO2 has been studied as a promising way to accelerate the transport of electrons and Na+ ions, which is important for achieving excellent electrochemical properties for anatase TiO2. However, wittingly introducing oxygen vacancies in anatase TiO2 for sodium-ion anodes by a facile and effective method is still a challenge. In this work, we report an innovative method to introduce oxygen vacancies into the urchin-like N-doped carbon coated anatase TiO2 (NC-DTO) by a facile plasma treatment. The superiorities of the oxygen vacancies combined with the conductive N-doped carbon coating enable the obtained NC-DTO of greatly improved sodium storage performance. When served as the anode for sodium-ion batteries, the NC-DTO electrode shows superior electrochemical performance (capacity: 272 mA h g-1 at 0.25 C, capacity retention: 98.8% after 5000 cycles at 10 C, as well as ultrahigh capacity: 150 mA h g-1 at 15 C). Density functional theory calculations combined with experimental results suggest that considerably improved sodium storage performance of NC-DTO is due to the enhanced electronic conductivity from the N-doped carbon layer as well as narrowed band gap and lowered sodiation energy barrier from the introduction of oxygen vacancies. This work highlights that introducing oxygen vacancies into TiO2 by plasma is a promising method to enhance the electrochemical property of TiO2, which also can be applied to different metal oxides for energy storage devices.

8.
ACS Appl Mater Interfaces ; 9(7): 6093-6103, 2017 Feb 22.
Artigo em Inglês | MEDLINE | ID: mdl-28121119

RESUMO

Developing advanced anodes for sodium ion batteries is still challenging. In this work, Fe-doped three-dimensional (3D) cauliflower-like rutile TiO2 was successfully synthesized by a facile hydrolysis method followed by a low-temperature annealing process. The influence of Fe content on the structure, morphology, and electrochemical performance was systematically investigated. When utilized as a sodium ion battery anode, 6.99%-Fe-doped TiO2 exhibited the best electrochemical performance. This sample delivered a very high reversible capacity (327.1 mAh g-1 at 16.8 mA g-1) and superior rate performance (160.5 mAh g-1 at 840 mA g-1), as well as long-term cycling stability (no capacity fading at 1680 mA g-1 over 3000 cycles). Density functional theory (DFT) calculations combined with experimental results indicated that the significantly improved sodium storage ability of the Fe-doped sample should be mainly due to the increased oxygen vacancies, narrowed band gap, and lowered sodiation energy barrier, which enabled much higher electronic/ionic conductivities and more favorable sodium ion intercalation into rutile TiO2.

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