ИСТИНА

Li-air batteries are often considered to be the next generation battery technology, as theoretical predictions promise outstandingly high energy density around 1000 Wh/kg [1]. Such expectations are based on the low weight of active materials: metallic lithium (at the anode) and oxygen (at the cathode). To facilitate charge transfer and to provide space for insoluble reaction product (Li2O2) a conductive porous matrix most commonly made of carbon black is used as a cathode in Li-O2 cell. Optimizing of cathode morphology (pore size distribution, specific surface area) for the best cell performance is subject of many experimental [2] and theoretical [3] works, however it’s lack of the data about сathode pores filling by Li2O2 during discharge, because most frequently technique for studying it - SEM [2] says nothing about the distribution of the peroxide in the depth of the electrode. Here we first propose small-angle neutron scattering (SANS) study of carbon electrodes of Li-air battery cell. By this method 1-100 nm diameter pores can be investigated that, according to N2 absorption data, contribute most to the specific surface area. Additionally, in contrast to standard methods of pores size distribution evaluation, by tuning the isotopic composition of electrolyte SANS allow us to study samples wetted by variety of electrolytes and so get information about surface area that available for electrolyte and consequently electrochemical active. Carbon paper was used as an electrode material with controlled porosity. It was found that pores smaller than 10 nm diameter aren’t wetted by DMSO-based electrolyte so they don’t take part in oxygen reduction reaction. After filling app. 50% percent of 10 - 100 nm diameter pores by discharge product further discharge blocks regardless of the discharge current rate. Also formation of periodical structures with correlation length of about 3.5 nm was found that could be attributed to Li2O2 spherulites previously observed by SEM [4]. Based on these data we proposed model of cathode pore filling during battery discharge that can be used for further optimizing cathode structure.