A new Mn-based layered cathode with enlarged interlayer spacing for potassium ion batteries.

Layered Mn-based cathode (KxMnO2) has attracted wide attention for potassium ion batteries (PIBs) because of its high specific capacity and energy density. However, the structure and capacity of KxMnO2 cathode are constantly degraded during the cycling due to the strong Jahn-Teller effect of Mn3+ and huge ionic radius of K+. In this work, lithium ion and interlayer water were introduced into Mn layer and K layer in order to suppress the Jahn-Teller effect and expand interlayer spacing, respectively, thus obtaining new types of K0.4Mn1-xLixO2·0.33H2O cathode materials. The interlayer spacing of the K0.4MnO2 increased from 6.34 to 6.93 Å after the interlayer water insertion. X-ray photoelectron spectroscopy studies demonstrated that proper lithium doping can effectively control the ratio of Mn3+/Mn4+ and inhibit the Jahn-Teller effect. In-situ X-ray diffraction exhibited that lithium doping can inhibit the irreversible phase transition and improve the structural stability of materials during cycling. As a result, the optimal K0.4Mn0.9Li0.1O2·0.33H2O not only delivered a higher capacity retention of 84.04 % compared to the value of 28.09 % for K0.4MnO2·0.33H2O, but also maintained a greatly enhanced rate capability. This study provides a new opportunity for designing layered manganese-based cathode materials with high performance for PIBs.

Graphdiyne applied for electrochemical energy storage.

Graphdiyne as a new allotrope of carbon material was constructed by benzene rings and butadiyne. The large 2D conjugated structure endows graphdiyne with excellent conductivity and flexibility. More importantly, the atomic arrangement of graphdiyne with a unique porous framework structure is very different from the compact structure of other carbon materials, such as graphene and carbon nanotubes. This is of great benefit to the diffusion and transfer of ions and gases. In the meantime, the high specific surface area originating from the pore structure can also provide abundant active sites for the storage of electrons or ions. The high charge density around the acetylenic bond in graphdiyne supplies the adsorption capacity of ions and gases as well as the catalytic ability to some degree. In addition, the mild synthetic route endows graphdiyne with function tunability and good film-forming ability. Benefiting from all these extraordinary properties, graphdiyne would have a bright future for applications in electrochemical energy storage.

Artificial Thiophdiyne Ultrathin Layer as an Enhanced Solid Electrolyte Interphase for the Aluminum Foil of Dual-Ion Batteries.

In this study, we design a novel carbon-based material containing thiophene and acetylenic linkers as functional groups named thiophdiyne (Thi-Dy) and apply it as an ultrathin artificial protective layer for the commercially available aluminum (Al) foil of dual-ion batteries (DIBs). The Thi-Dy films can be grown easily and directly on the Al foil through a mild Glaser-Hay coupling reaction. The as-proposed thiophene and acetylenic linker functional groups in Thi-Dy layers act as energetic active sites for the effective fabrication of a stable hybrid solid electrolyte interphase (SEI) during the electrochemical process, which is revealed through the ex situ measurement. The Thi-Dy-enhanced SEI layer contributes to offer a more effective and regulated lithium intercalation and diffusion pathway and delay the pulverization and huge volume expansion of the Al-Li alloy during long cycles, which are confirmed by the improvement on the cyclic stability of DIBs. Those studies are expected to provide novel thiophene-containing functional materials and mass-produced surface modification approach for metal anode protection, which will promote the research for the next-generation rechargeable battery.

Fluorine-Enriched Graphdiyne as an Efficient Anode in Lithium-Ion Capacitors.

Lithium-ion capacitors (LICs) have shown extraordinary promise for electrochemical energy storage but are usually limited to electrodes with low energy density or power density owing to the lack of active storage sites and ion diffusion limitation. In this study, fluorine-enriched graphdiyne (F-GDY) is prepared by a solvothermal reaction. Owing to the 42-C hexagonal porous structure, abundant sp and sp2 hybrid carbon atoms, and even distribution of fluorine, F-GDY has enormous potential as an anode for lithium-ion storage. The outstanding rate performance (1825.9 mAh g-1 at 0.1 A g-1 , 979.2 mAh g-1 at 5 A g-1 ) and stable cycling stability of F-GDY in the lithium-ion battery inspire the assembly of a LIC with F-GDY as an anode and activated carbon (AC) as a cathode. When the AC/F-GDY mass ratio is 7:1, the LIC gives the largest energy density of 200.2 Wh kg-1 , corresponding to a power density of 131.17 W kg-1 . This LIC also shows excellent long-term cycling stability with a retention of approximately 80 % after 5000 cycles at 2 A g-1 and a retention of more than 80 % after 6000 cycles at 5 A g-1 .

Graphdiyne Containing Atomically Precise N Atoms for Efficient Anchoring of Lithium Ion.

The qualitative and quantitative nitrogen-doping strategy for carbon materials is reported here. Novel porous nanocarbon networks pyrimidine-graphdiyne (PM-GDY) and pyridine-graphdiyne (PY-GDY) films with large areas were successfully prepared. These films are self-supported, uniform, continuous, flexible, transparent, and quantitively doped with merely pyridine-like nitrogen (N) atoms through the facile chemical synthesis route. Theoretical predictions imply these N doped carbonaceous materials are much favorable for storing lithium (Li)-ions since the pyridinic N can enhance the interrelated binding energy. As predicted, PY-GDY and PM-GDY display excellent electrochemical performance as anode materials of LIBs, such as the superior rate capability, the high capacity of 1168 (1165) mA h g-1 at current density of 100 mA g-1 for PY-GDY (PM-GDY), and the excellent stability of cycling for 1500 (4000) cycles at 5000 mA g-1 for PY-GDY (PM-GDY).

Construction of Large-Area Uniform Graphdiyne Film for High-Performance Lithium-Ion Batteries.

Large-area graphdiyne film is constructed by heat treatment, including thermally induced evaporation and a cross-coupling reaction process. The growth mechanism is proposed based on the observation and characterization that the heating temperature plays an important role in the evaporation of oligomers and in triggering the thermal cross-coupling reaction, whereas the heating duration mainly determines the execution of the thermal cross-coupling reaction. By controlling the heat-treatment process, a graphdiyne film with uniform morphology and good conductivity is obtained. The improved GDY film based electrodes deliver good interfacial contact and more lithium storage sites; thus leading to superior electrochemical performance. A reversible capacity of 901 mAh g-1 is achieved. Specifically, the electrodes exhibit excellent rate performance, with which a capacity of 430 mAh g-1 is maintained at a rate as high as 5 A g-1 . These advantages mean that the uniform graphdiyne film is a good candidate for the fabrication of a flexible and high-capacity electrode material.

Preparation of 3D Architecture Graphdiyne Nanosheets for High-Performance Sodium-Ion Batteries and Capacitors.

Here, we apply three-dimensional (3D) architecture graphdiyne nanosheet (GDY-NS) as anode materials for sodium-ion storage devices achieving high energy and power performance along with excellent cyclic ability. The contribution of 3D architecture nanostructure and intramolecular pores of the GDY-NS can substantially optimize the sodium storage behavior through the accommodated intramolecular pore, 3D interconnective porous structure, and increased activity sites to facilitate a fast sodium-ion-diffusion channel. The contribution of butadiyne linkages and the formation of a stable solid electrolyte interface layer are directly confirmed through the in situ Raman measurement. The GDY-NS-based sodium-ion batteries exhibit a stable reversible capacity of approximately 812 mAh g-1 at a current density of 0.05 A g-1; they maintain more than 405 mAh g-1 over 1000 cycles at a current density of 1 A g-1. Furthermore, the sodium-ion capacitors could deliver a capacitance more than 200 F g-1 over 3000 cycles at 1 A g-1 and display an initial specific energy as high as 182.3 Wh kg-1 at a power density of 300 W kg-1 and maintain specific energy of 166 Wh kg-1 even at a power density of 15 000 W kg-1. The high energy and power density along with excellent cyclic performance based on the GDY-NS anode offers a great potential toward application on next-generation energy storage devices.

Hydrogen substituted graphdiyne as carbon-rich flexible electrode for lithium and sodium ion batteries.

Organic electrodes are potential alternatives to current inorganic electrode materials for lithium ion and sodium ion batteries powering portable and wearable electronics, in terms of their mechanical flexibility, function tunability and low cost. However, the low capacity, poor rate performance and rapid capacity degradation impede their practical application. Here, we concentrate on the molecular design for improved conductivity and capacity, and favorable bulk ion transport. Through an in situ cross-coupling reaction of triethynylbenzene on copper foil, the carbon-rich frame hydrogen substituted graphdiyne film is fabricated. The organic film can act as free-standing flexible electrode for both lithium ion and sodium ion batteries, and large reversible capacities of 1050 mAh g-1 for lithium ion batteries and 650 mAh g-1 for sodium ion batteries are achieved. The electrode also shows a superior rate and cycle performances owing to the extended π-conjugated system, and the hierarchical pore bulk with large surface area.