Air sensitivity of electrode materials in Li/Na ion batteries:Issues and strategies

With the development of electrode materials in lithium ion batteries-upgrading from LiCoO_(2)and LiFePO_(4)to Ni-rich layered oxides,and the shifting of battery systems from high cost lithium ion to low cost sodium ion technology,the air sensitivity of the electrode materials has become an increasingly important issue in both production and application.Furthermore,the air sensitivity of electrode materials must be carefully considered throughout nearly all stages of their life,including material design,synthesis,production,storage,packaging,transportation,and battery assembly.Therefore,a fundamental understanding of the air degradation mechanism of electrode materials and the exploration of new methods to enhance their air stability are of great significance for the development of batteries with better performance.Herein,we provide a review of the issues related to air exposure of electrode materials in Li/Na ion batteries,including factors related to air sensitivity,degradation mechanisms,and recent progress in improving their air stability.The merits and existing challenges of different strategies are presented,and a rational design perspective as well as general principles for evaluating air stability are proposed.

Ignition enhancement of ethylene/air by NO_x addition

Recently, non-equilibrium plasma assisted combustion （PAC） has been found to be promising in reducing the ignition delay time in hypersonic propulsion system. NO x produced by non-equilibrium plasma can react with intermediates during the fuel oxidation process and thereby has influence on the combustion process. In this study, the effects of NO x addition on the ignition process of both the homogeneous ethylene/air mixtures and the non-premixed diffusion layer are examined numerically. The detailed chemistry for ethylene oxidization together with the NO x sub-mechanism is included in the simulation. Reaction path analysis and sensitivity analysis are conducted to give a mechanistic interpretation for the ignition enhancement by NO x addition. It is found that for both the homogenous and non-premixed ignition processes at normal and elevated pressures, NO 2 addition has little influence on the ignition delay time while NO addition can significantly promote the ignition process. The ignition enhancement is found to be caused by the promotion in hydroxyl radical production which quickly oxidizes ethylene. The promotion in hydroxyl radical production by NO addition is achieved in two ways：one is the direct production of OH through the reaction HO2＋NO = NO2＋OH, and the other is the indirect production of OH through the reactions NO＋O2=NO2＋O and C2H4＋O = C2H3＋OH. Moreover, it is found that similar to the homogeneous ignition process, the acceleration of the diffusion layer ignition is also controlled by the reaction HO2＋NO = NO2＋OH.