ИСТИНА

As Li-air batteries (LAB) can potentially store up to 5 times more energy per unit weight than Li-ion, current research efforts are focused on their rechargeability issues. Since deposition of discharge products, i.e. lithium peroxide (Li2O2), inside a positive electrode can strongly affect the battery performance [1], a careful control and detailed understanding of such processes are required for achieving deeper discharge and complete reversibility. One of the intermediate processes that precedes formation of lithium peroxide is the disproportionation of electrochemically generated superoxide (LiO2) [2]. The rate of this reaction significantly impacts the morphology of the deposited particles and, consequently, the efficiency of cathode material pore volume filling, as well as the electronic and ionic conductivities of the resulting precipitate. In turn, these factors significantly affect the rechargeability. Here, we use cyclic voltammetry (CV) on glassy carbon electrode to evaluate influence of electrolyte solvent on LiO2 disproportionation rate and diffusivity by studying the rate of Li2CO3 formation. LiO2 reacts with carbon resulting Li2CO3 [3], which can be oxidized only at high anodic overpotentionals. LiO2 solvation and diffusivity govern its activity in the mentioned side reaction and its concentration near electrode surface, respectively. Thin film of Li2CO3 on the electrode surface block further electron transport from the electrode surface to molecular oxygen and decrease cathodic flowing charge. So tracking the changes of cathodic charge during cycling can give information about the rate of Li2CO3 formation. We studied the electrolytes based on the solvents that are widely used in Li-O2 battery research: DMSO, MeCN, DME, TMS, DMA, DMF, NMP [4]. We found that, in general, Li2CO3 passivation rate correlates with the increase of Li+ solvation ability, which can be roughly characterized by solvent donor number [2]. Surprisingly, amide solvents (DMA, DMF, NMP) demonstrate much higher passivation rate than can be expected. We suppose that it can be connected with amide intrinsic instability in ORR reaction conditions. In contrast, lower passivation rate than expected is observed for TMS-based electrolyte that is possibly connected with its high viscosity affecting transport.