Thermal runaway of Lithium-ion batteries employing LiN(SO2F)2-based concentrated electrolytes.

Concentrated electrolytes usually demonstrate good electrochemical performance and thermal stability, and are also supposed to be promising when it comes to improving the safety of lithium-ion batteries due to their low flammability. Here, we show that LiN(SO2F)2-based concentrated electrolytes are incapable of solving the safety issues of lithium-ion batteries. To illustrate, a mechanism based on battery material and characterizations reveals that the tremendous heat in lithium-ion batteries is released due to the reaction between the lithiated graphite and LiN(SO2F)2 triggered thermal runaway of batteries, even if the concentrated electrolyte is non-flammable or low-flammable. Generally, the flammability of an electrolyte represents its behaviors when oxidized by oxygen, while it is the electrolyte reduction that triggers the chain of exothermic reactions in a battery. Thus, this study lights the way to a deeper understanding of the thermal runaway mechanism in batteries as well as the design philosophy of electrolytes for safer lithium-ion batteries.

Over 14% Efficiency in Organic Solar Cells Enabled by Chlorinated Nonfullerene Small-Molecule Acceptors.

To make organic solar cells (OSCs) more competitive in the diverse photovoltaic cell technologies, it is very important to demonstrate that OSCs can achieve very good efficiencies and that their cost can be reduced. Here, a pair of nonfullerene small-molecule acceptors, IT-2Cl and IT-4Cl, is designed and synthesized by introducing easy-synthesis chlorine substituents onto the indacenodithieno[3,2-b]thiophene units. The unique feature of the large dipole moment of the CCl bond enhances the intermolecular charge-transfer effect between the donor-acceptor structures, and thus expands the absorption and down shifts the molecular energy levels. Meanwhile, the introduction of CCl also causes more pronounced molecular stacking, which also helps to expand the absorption spectrum. Both of the designed OSCs devices based on two acceptors can deliver a power conversion efficiency (PCE) greater than 13% when blended with a polymer donor with a low-lying highest occupied molecular orbital level. In addition, since IT-2Cl and IT-4Cl have very good compatibility, a ternary OSC device integrating these two acceptors is also fabricated and obtains a PCE greater than 14%. Chlorination demonstrates effective ability in enhancing the device performance and facile synthesis route, which both deserve further exploitation in the modification of photovoltaic materials.

Van der Waals Coupled Organic Molecules with Monolayer MoS2 for Fast Response Photodetectors with Gate-Tunable Responsivity.

As a direct-band-gap transition metal dichalcogenide (TMD), atomic thin MoS2 has attracted extensive attention in photodetection, whereas the hitherto unsolved persistent photoconductance (PPC) from the ungoverned charge trapping in devices has severely hindered their employment. Herein, we demonstrate the realization of ultrafast photoresponse dynamics in monolayer MoS2 by exploiting a charge transfer interface based on surface-assembled zinc phthalocyanine (ZnPc) molecules. The formed MoS2/ZnPc van der Waals interface is found to favorably suppress the PPC phenomenon in MoS2 by instantly separating photogenerated holes toward the ZnPc molecules, away from the traps in MoS2 and the dielectric interface. The derived MoS2 detector then exhibits significantly improved photoresponse speed by more than 3 orders (from over 20 s to less than 8 ms for the decay) and a high responsivity of 430 A/W after Al2O3 passivation. It is also demonstrated that the device could be further tailored to be 2-10-fold more sensitive without severely sacrificing the ultrafast response dynamics using gate modulation. The strategy presented here based on surface-assembled organic molecules may thus pave the way for realizing high-performance TMD-based photodetection with ultrafast speed and high sensitivity.

Achieving Highly Efficient Nonfullerene Organic Solar Cells with Improved Intermolecular Interaction and Open-Circuit Voltage.

A new acceptor-donor-acceptor-structured nonfullerene acceptor ITCC (3,9-bis(4-(1,1-dicyanomethylene)-3-methylene-2-oxo-cyclopenta[b]thiophen)-5,5,11,11-tetrakis(4-hexylphenyl)-dithieno[2,3-d':2,3-d']-s-indaceno[1,2-b:5,6-b']-dithiophene) is designed and synthesized via simple end-group modification. ITCC shows improved electron-transport properties and a high-lying lowest unoccupied molecular orbital level. A power conversion efficiency of 11.4% with an impressive V OC of over 1 V is recorded in photovoltaic devices, suggesting that ITCC has great potential for applications in tandem organic solar cells.

One-pot synthesis of Li3VO4@C nanofibers by electrospinning with enhanced electrochemical performance for lithium-ion batteries.

Electrospinning is firstly used to one-pot synthesis of Li3VO4@C nanofibers in a large scale. Although with the presence of organic sources in synthesis process, the pure phase Li3VO4 with superior nanofibrous morphology is still successfully obtained through adjusting different heat treatment processes and different vanadium sources. The prepared Li3VO4@C nanofibers exhibit a unique structure in which nanosized Li3VO4 particles are uniformly embedded in amorphous carbon matrix. Compared with Li3VO4/C powder, Li3VO4@C nanofibers display enhanced reversible capacity of 451mAhg-1 at 40mAg-1 with an increased initial coulombic efficiency of 82.3%, and the capacity can remain at 394mAhg-1 after 100 cycles. This superior electrochemical performance can be attributed to its unique structure which ensures a high reactivity by nanosized Li3VO4, more stable electrode/electrolyte interface by carbon encapsulation, improved electronic conductivity and buffered volume changes by flexible carbon matrix. The electrospinning technology provides an effective method to obtain high performance Li3VO4 as a promising anode material for lithium-ion batteries.

A comparative study of graphene-coated stainless steel fiber felt and carbon cloth as anodes in MFCs.

This study investigated the stainless steel-based materials and their potential in microbial fuel cells (MFCs) anode application. Herein, AISI 316L stainless steel fiber felts (SSFFs) were used as anodes in MFCs and their performance was compared with the carbon cloth anode MFCs. The experimental results showed that the unmodified carbon cloth (CC) anode had a better performance than the unmodified SSFF anode. However, after coating a thin layer of graphene (GN) on SSFF and CC, the power density of the MFC equipped with the modified SSFF was 2,143 mW m(-2), much higher than that of the graphene-modified CC-MFC which was only 1,018 mW m(-2). The experimental results proved that the use of durable metallic backbones combined with a thin layer of carbon nanoparticles offers exciting opportunities in the advancement of MFC anode design.