Chemical interaction motivated structure design of layered metal carbonate hydroxide/MXene composites for fast and durable lithium ion storage

Rational architecture design has turned out to be an effective strategy in improving the electrochemical performance of electrode materials for batteries.However,an elaborate structure that could simultaneously endow active materials with promoted reaction reversibility,accelerated kinetic and restricted volume change still remains a huge challenge.Herein,a novel chemical interaction motivated structure design strategy has been proposed,and a chemically bonded Co(CO_(3))_(0.5)OH·0.11 H_(2)O@MXene(CoCH@MXene)layered-composite was fabricated for the first time.In such a composite,the chemical interaction between Co^(2+)and MXene drives the growth of smaller-sized CoCH crystals and the subsequent formation of interwoven CoCH wires sandwiched in-between MXene nanosheets.This unique layered structure not only encourages charge transfer for faster reaction dynamics,but buffers the volume change of CoCH during lithiation-delithiation process,owing to the confined crystal growth between conductive MXene layers with the help of chemical bonding.Besides,the sandwiched interwoven CoCH wires also prevent the stacking of MXene layers,further conducive to the electrochemical performance of the composite.As a result,the as-prepared CoCH@MXene anode demonstrates a high reversible capacity(903.1 mAh g^(-1)at 100 mA g^(-1))and excellent cycling stability(maintains 733.6 mAh g^(-1)at1000 mA g^(-1)after 500 cycles)for lithium ion batteries.This work highlights a novel concept of layerby-layer chemical interaction motivated architecture design for futuristic high performance electrode materials in energy storage systems.

Horizontal oscillation processed large MXene with Low Ti–Ti coordination for fast sodium storage

MXene stands out as a rising family of transition metal carbides/nitrides with exceptional size-dependent properties and versatile potential applications. However, the realization of large MXene with a controllable surface at atomic level remains challenging to keep the balance among the conductivity, stability and activity. Herein, the horizontal oscillation-induced delamination(HOD)strategy is proposed to acquire Ti_(3)C_(2) flakes with large size and low Ti–Ti coordination(HO-Ti_(3)C_(2)). The average size of the asobtained flakes can reach 6.48 μm to keep the overall conductive skeleton and merits from large size. Simultaneously, metal atoms at surface can be partially removed due to the enhanced local vibrational turbulence during the reciprocating horizontal oscillation process. Such MXenes with clear and unique surface states exhibit high potentials in ion adsorption together with satisfied electric conductivity and stability. As proof of concept, HO-Ti_(3)C_(2) anode exhibits remarkable rate capability and longterm stability during sodium storage. A capacity of 100.5 m Ah g^(-1)with a long-life cycle(4,500 cycles) at a high rate of 1.0 A g^(-1)originates from the increased s-d interaction between Na and Ti. Therefore, the HOD strategy provides a controllable surface design to promote the clear criteria into size-dependent research on MXene.

Tailored amorphous titanium oxide and carbon composites for enhanced pseudocapacitive sodium storage

As an effective and competitive supplement to the commercialized lithium ion batteries(LIBs),sodium ion batteries(SIBs)have been receiving increasing attention in recent years due to lower cost,richer content,and broader distribution of sodium[1–7].Sodium has similar electrochemical properties to lithium,and thus the concepts for the preparation of electrode materials for SIBs can be borrowed from LIBs[8,9].

Insights into the stable and fast lithium storage performance of oxygen-deficient LiV_(3)O_(8) nanosheets

Oxygen-deficient LiV_(3)O_(8) is considered as one of the promising cathode materials for lithium ion batteries(LIBs)because of its high cycling stability and rate capability.However,it is very difficult to control and study the content and position of V^(4+)and oxygen vacancies in LiV_(3)O_(8),and therefore the mechanism of improving electrochemical performance of LiV_(3)O_(8) is still unclear.Herein,we developed four LiV_(3)O_(8) nanosheets with different V^(4+)and oxygen vacancy contents and positions.The physicochemical and lithium storage properties indicate that the V^(4+)and oxygen vacancies in the surface layer increase the contribution of pseudocapacitive lithium storage on the nanosheet surface.The V^(4+)and oxygen vacancies in the lattice improve the electrical conductivity of LiV_(3)O_(8),and enhance the phase transformation and lithium ion diffusion rates.By adjusting the content of V^(4+)and oxygen vacancies,we obtained an oxygen-deficient LiV_(3)O_(8) nanosheet which maintained more than 93%of the initial reversible capacity after 300 cycles at 5,000 mA·g^(−1).The V^(4+)and oxygen vacancies play an important role in improving the stability and rapidity of lithium storage.This work is helpful to understand the stable and fast lithium storage mechanism of oxygen-deficient LiV_(3)O_(8),and might lay a foundation for further studies of other oxygen-deficient metal oxide electrodes for long-life and high-power LIBs.

Wire-Shaped 3D-Hybrid Supercapacitors as Substitutes for Batteries

We report a wire-shaped three-dimensional(3D)-hybrid supercapacitor with high volumetric capacitance and high energy density due to an interconnected 3D-configuration of the electrode allowing for large number of electrochemical active sites,easy access of electrolyte ions,and facile charge transport for flexible wearable applications.The interconnected and compact electrode delivers a high volumetric capacitance(gravimetric capacitance)of 73 F cm−3(2446 F g−1),excellent rate capability,and cycle stability.The 3D-nickel cobalt-layered double hydroxide onto 3D-nickel wire(NiCo LDH/3D-Ni)//the 3D-manganese oxide onto 3D-nickel wire(Mn3O4/3D-Ni)hybrid supercapacitor exhibits energy density of 153.3 Wh kg−1 and power density of 8810 W kg−1.The red lightemitting diode powered by the as-prepared hybrid supercapacitor can operate for 80 min after being charged for tens of seconds and exhibit excellent electrochemical stability under various deformation conditions.The results verify that such wire-shaped 3D-hybrid supercapacitors are promising alternatives for batteries with long charge–discharge times,for smart wearable and implantable devices.