Thermal Runaway of Lithium-Ion Batteries Employing Flame-Retardant Fluorinated Electrolytes

Fluorinated electrolytes possess good antioxidant capacity that provides high compatibility to high-voltage cathode and flame retardance;thus,they are considered as a promising solution for advanced lithium-ion batteries carrying both high-energy density and high safety.Moreover,the fluorinated electrolytes are widely used to form stable electrolyte interphase,due to their chemical reactivity with lithiated graphite or lithium.However,the influence of this reactivity on the thermal safety of batteries is seldom discussed.Herein,we demonstrate that the flame-retardant fluorinated electrolytes help to reduce the flammability,while the lithium-ion batteries with flame-retardant fluorinated electrolytes still undergo thermal runaway and disclose their different thermal runaway pathway from that of battery with conventional electrolyte.The reduction in fluorinated components(e.g.,LiPF 6 and fluoroethylene carbonate(FEC))by fully lithiated graphite accounts for a significant heat release during battery thermal runaway.The 13%of total heat is sufficient to trigger the chain reactions during battery thermal runaway.This study deepens the understanding of the thermal runaway mechanism of lithium-ion batteries employing flame-retardant fluorinated electrolytes,providing guidance on the concept of electrolyte design for safer lithium-ion batteries.

Full electromagnetic transient simulation for large power systems

For building Global Energy Interconnection(GEI), it is necessary to implement new breakthroughs on largepower system simulation. Key routes for implementing full electromagnetic transient simulation of large-power systems are described in this paper, and a top framework is designed. A combination of the new large time step algorithm and the traditional small-time step algorithm is proposed where both parts A and B are calculated independently. The method for integrating the Norton equivalence of the power electronic system to the entire power grid is proposed. A two-level gird division structure is proposed, which executes a multi-rate parallel calculation among subsystems and element parallel calculation in each subsystem. The initialization method of combining load flow derivation and automatic trial-and-error launching is introduced. The feasibility of the method is demonstrated through a practical power grid example, which lays a foundation for further research.

Acid promoted Ni/NiO monolithic electrode for overall water splitting in alkaline medium

Exploring and designing bi-functional catalysts with earth-abundant elements that can work well for both hydrogen evolution reaction（HER） and oxygen evolution reaction（OER） in alkaline medium are of significance for producing clean fuel to relieve energy and environment crisis.Here,a novel Ni/NiO monolithic electrode was developed by a facile and cost-effective acid promoted activation of Ni foam.After the treatment,this obtained monolithic electrode with a layer of NiO on its surface demonstrates rough and sheet-like morphology,which not only possesses larger accessible surface area but also provides more reactive active sites. Compared with powder catalysts,this monolithic electrode can achieve intimate contact between the electrocatalyst and the current collector,which will alleviate the problem of pulverization and enable the stable function of the electrode. It can be served as an efficient bi-functional electrocatalyst with an overpotential of 160 mV for HER and 290 mV for OER to produce current densities of 10 mA cm^（-2） in the alkaline medium. And it maintains benign stability after 5,000 cycles,which rivals many recent reported noble-metal free catalysts in 1.0mol L^（-1） KOH solution. Attributed to the easy,scalable methodology and high catalytic efficiency,this work not only offers a promising monolithic catalyst but also inspires us to exploit other inexpensive,highly efficient and self-standing noble metalfree electrocatalysts for scale-up electrochemical water-splitting technology.

One-pot synthesis of Li_3VO_4@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 LiBVO4/C powder, Li3VO4@C nanofibers display enhanced reversible capacity of 451 mAhg^-1 at 40mAg^-1 with an increased initial coulombic efficiency of 82.3%, and the capacity can remain at 394 mAh g ^-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.