A 2D covalent organic framework with ultra-large interlayer distance as high-rate anode material for lithium-ion batteries

Covalent organic frameworks(COFs)have been broadly investigated for energy storage systems.However,many COF-based anode materials suffer from low utilization of redox-active sites and sluggish ions/electrons transport caused by their densely stacked layers.Thus,it is still a great challenge to obtain COF-based anode materials with fast ions/electrons transport and thus superior rate performance.Herein,a redox-active piperazine-terephthalaldehyde(PA-TA)COF with ultra-large interlayer distance is designed and synthesized for high-rate anode material,which contains piperazine units adopting a chair-shaped conformation with the nonplanar linkages of a tetrahedral configuration.This unique structure renders PA-TA COF an ultra-large interlayer distance of 6.2Å,and further enables it to achieve outstanding rate and cycling performance.With a high specific capacity of 543 mAh·g^(−1) even after 400 cycles at 1.0 A·g^(−1),it still could afford a specific capacity of 207 mAh·g^(−1) even at a high current density of 5.0 A·g^(−1).Our study indicates that expanding the interlayer distance of COFs by rational molecular design would be of great importance to develop high-rate electrode materials for lithium-ion batteries.

K+alkalization promoted Ca2+intercalation in V2CTx MXene for enhanced Li storage

Although MXenes is highly attractive as anode materials of lithium ion batteries,it sets a bottleneck for higher capacity of the V2CTxMXene due to the limited interlayer space and the derived surface terminations.Herein,the cation intercalation and ion-exchange were well employed to achieve a K+and Ca2+intercalated V2CTxMXene.A larger interlayer distance and low F surface terminations were thereof obtained,which accelerates the ion transport and promotes the delicate surface of V2CTx MXene.As a result,a package of enhanced capacity,rate performance and cyclability can be achieved.Furthermore,the ion exchange approach can be extended to other 2 D layered materials,and both the interlayer control and the surface modification will be achieved.

There is plenty of space in the MXene layers: The confinement and fillings

MXenes have emerged as a new kind of 2D transition metal carbides,nitrides and carbonitrides.Origined from the unique 2D structure with a luxuriant combination of elements,MXenes drive a series of the investigations related to energy storage and conversion,biometrics and sensing,lighting,purification and separation.For 2D layered MXene materials,the interspacing confined by the independent MXenes layers affords a distinct confinement space,which is similar to a nanoreactor that can be utilized for the storage of ions,nanoparticles,nanowires,and the materials with 2D or 3D structure.These fillings confined by MXene layers afford new opptunities for achieving improved properties and performance via complementary natural features,further the synergistic effect.Herein,we summarize the recent reports concerning with the confinded MXenes spacing and the fillings.The modification of interlayer distance lead by the intercalants were explored.We expect that our review may offer the route for a series of ongoing studies to address the MXenes.

Fullerene-Intercalated Graphitic Carbon Nitride as a HighPerformance Anode Material for Sodium-Ion Batteries

Two-dimensional(2D)graphitic carbon nitride(g-CN)is a promising anode material for sodium-ion batteries(SIBs),but its insufficient interlayer spacing and poor electronic conductivity impede its sodium storage capacity and cycling stability.Herein,we report the fabrication of a fullerene(C_(60))-modified graphitic carbon nitride(C_(60)@CN)material which as an anode material for SIBs shows a high-reversible capacity(430.5 mA h g^(−1) at 0.05 A g^(−1),about 3 times higher than that of pristine g-CN),excellent rate capability(226.6 mA h g^(−1) at 1 A g^(−1))and ultra-long cycle life(101.2 mA h g^(−1) after 5000 cycles at 5 A g^(−1)).Even at a high-active mass loading of 3.7 mg cm^(−2),a reversible capacity of 316.3 mA h g^(−1) can be obtained after 100 cycles.Such outstanding performance of C_(60)@CN is attributed to the C_(60) molecules distributed in the g-CN nanosheets,which enhance the electronic conductivity and prevent g-CN sheets from restacking,thus resulting in enlarged interlayer spacing and exposed edge N defects(pyridinic N and pyrrolic N)for sodium-ion storage.Furthermore,a sodium-ion full cell combining C60@CN anode and NVPF@rGO cathode provides high-coulombic efficiency(>96.5%),exceptionally high-energy density(359.8 W h kganode−1 at power density of 105.1 W kganode−1)and excellent cycling stability(89.2%capacity retention over 500 cycles at 1Aganode−1).This work brings new insights into the field of carbon-based anode materials for SIBs.

Layered barium vanadate nanobelts for high-performance aqueous zinc-ion batteries

Aqueous zinc-ion batteries(ZIBs)are deemed as the idea option for large-scale energy storage systems owing to many alluring merits including low manufacture cost,environmental friendliness,and high operations safety.However,to develop high-performance cathode is still significant for practical application of ZIBs.Herein,Ba_(0.23)V_(2)O_(5)·1.1H_(2)O(BaVO)nanobelts were fabricated as cathode materials of ZIBs by a typical hydrothermal synthesis method.Benefiting from the increased interlayer distance of 1.31 nm by Ba2+ and H2O pre-intercalated,the obtained BaVO nanobelts showed an excellent initial discharge capacity of 378 mAh·g^(-1) at 0.1 A·g^(-1),a great rate performance(e.g.,172 mAh·g^(-1) at 5 A·g^(-1)),and a superior capacity retention(93% after 2000 cycles at 5 A·g^(-1)).

Aqueous Zn-MnO_(2) battery: Approaching the energy storage limit with deep Zn^(2+) pre-intercalation and revealing the ions insertion/extraction mechanisms

Rechargeable aqueous zinc ion batteries(AZIBs)were considered as one of the most promising candidates for large-scale energy storage due to the merits of high safety and inexpensiveness.As AZIBs cathode material,Mn O_(2)possesses great merits but was greatly hindered due to the sluggish diffusion kinetic of Zn^(2+) during electrochemical operations.Herein,deep Zn^(2+) ions intercalatedδ-Mn O_(2)(Zn-Mn O_(2))was achieved by the in situ electrochemical deposition route,which significantly enhanced the diffusion ability of Zn^(2+) due to the synergistic effects of Zn^(2+) pillars and structural H;O.The resultant Zn-Mn O_(2)based AZIBs delivers a record capacity of 696 m Ah/g(0.5 m Ah/cm^(2))based on the initial mass loading,which is approaching the theoretical capacity of Mn O_(2)with a two-electrons reaction.In-situ Raman studies reveal highly reversible Zn^(2+)ions insertion/extraction behaviors and here the Zn-Mn O_(2)plays the role of a container during the charge–discharge process.Further charge storage mechanism investigations point out the insertion/extraction of Zn^(2+) and H^(+) coincides,and such process is significantly facilitated results from superior interlayered configurations of Zn-Mn O_(2)The excellent electrochemical performance of Zn-Mn O_(2)achieved in this work suggests the deep ions pre-intercalation strategy may aid in the future development of advanced cathodes for AZIBs.

Study on Synthesis and Intercalation Behavior of Layered Zirconium Proline-N-methylphosphonate-phosphate

Zirconium proline-N-methylphosphonate-phosphate (α-ZPMPP) was prepared in the presence of HF for the first time. The a-ZPMPP sample is highly crystallized with interlayer distance of 1.52 nm. The interlayer distance of complex of α-ZPMPP with n-butylamine (α-ZPMPP-BA) is in 0.45 nm larger than that of α-ZPMPP. The α-ZPMPP possesses different intercalation behavior of host-guest compound from α-ZP.

Conformation of Organic Chain in Phase Transition of Hybrid(C1_2H_(25)NH_3)_2MnCl_4

The structural change in phase transition of hybrid （Cl2H25NH3）2MnCl4 was investigated. The temperature and the structures of the phase transition is investigated by thermal gravimetry （TG） and differential scanning calorimetry （DSC）, infrared spectrum （IR） and X-ray diffraction （XRD）. The results suggest that the phase transition is reversible and the structural change arises from the conformation change of the organic chain. The interlayer distance increases when the hybrid transforms from low temperature phase to high temperature phase. This is explained by the diffusion of gauche-bond along the organic chains and they move away from each other when the phase transition occurs. Combining the experimental data with theoretical calculation, we propose that organic chain of the hybrid in high temperature phase is the conformation of gauche-bond alternating with trans bond （noted as GTG＇TGTG＇TGTG＇T）.

Preparation and Properties of Oxidized Graphite Anode Doped with Metal Ion for Lithium Ion Batteries

Chemical oxidation and metal intercalation of natural graphite was utilized to increase the capacity and enhance the cycle property of graphite anodes in lithium ion batteries.

Highly Fluorescent Semiconducting Two-Dimensional Conjugated Polymer Films Achieved by Side-Chain Engineering Showing Large Exciton Diffusion Length

Semiconducting two-dimensional conjugated polymers(2DCPs)with strong fluorescence emission have great potential for various optoelectronic applications.However,it is enormously challenging to achieve this goal due to the significant compact interlayerπ-πstacking-induced quenching effect in these systems.In this work,we found that highly fluorescent semiconducting 2DCPs can be prepared through an effective side-chain engineering approach in which interlayer spacers are introduced to reduce the fluorescence quenching effect.The obtained two truxene-based 2DCP films that,along with-C6H13 and-C_(12)H_(25)alkyl side chains as interlayer spacers both demonstrate superior fluorescence properties with a high photoluminescence quantum yield of 5.6%and 14.6%,respectively.These are among the highest values currently reported for 2DCP films.Moreover,an ultralong isotropic quasi-twodimensional exciton diffusion length constrained in the plane with its highest value approaching 110 nm was revealed by the transient photoluminescence microscopy technique,suggesting that theπ-conjugated structure in these truxene-based 2DCP films has effectively been extended.This work can enable a broad exploration of highly fluorescent semiconducting 2DCP films for more deeply fundamental properties and optoelectronic device applications.

Flexible and highly-sensitive pressure sensor based on controllably oxidized MXene

Conductive Ti_(3)C_(2)T_(x)MXenes have been widely investigated for the construction of flexible and highly-sensitive pressure sensors.Although the inevitable oxidation of solution-processed MXene has been recognized,the effect of the irreversible oxidation of MXene on its electrical conductivity and sensing properties is yet to be understood.Herein,we construct a highly-sensitive and degradable piezoresistive pressure sensor by coating Ti_(3)C_(2)T_(x)MXene flakes with different degrees of in situ oxidation onto paper substrates using the dipping-drying method.In situ oxidation can tune the intrinsic resistance and expand the interlayer distance of MXene nanosheets.The partially oxidized MXene-based piezoresistive pressure sensor exhibits a high sensitivity of 28.43 kPa^(-1),which is greater than those of pristine MXene,over-oxidized MXene,and state-of-the-art paper-based pressure sensors.Additionally,these sensors exhibit a short response time of 98.3 ms,good durability over 5000 measurement cycles,and a low force detection limit of 0.8 Pa.Moreover,MXene-based sensing elements are easily degraded and environmentally friendly.The MXene-based pressure sensor shows promise for practical applications in tracking body movements,sports coaching,remote health monitoring,and human–computer interactions.