The paper presents the results of a computer simulation of lithium peroxide formation accompanying the discharge of a lithium-air battery (LAB). Two models (biporous and regular biporous) of the structure of the cathode active layer (AL) were compared based on our previous computer simulation of LAB discharge. The use of the regular biporous model was shown to be preferable. The effect of the initial pore radius in the cathode AL on the discharge characteristics was revealed. The discharge characteristics were significantly improved when the initial pore size increased. The use of the regular biporous model together with an attempt to increase the initial pore radius in the cathode AL structure makes it possible to increase the current density and specific capacity of the cathode during LAB discharge by several orders of magnitude.

The results of digital simulation of the lithium peroxide formation during the lithium–oxygen battery discharge are presented. The active layer of the positive electrode is described by the simplest monoporous model of a porous medium (a set of sinuous homogeneous non-intersecting pores of constant radius). The influence of the active layer thickness on the positive electrode dimensional characteristics during the galvanostatic discharge of the lithium–oxygen battery is investigated. The dependence of the discharge capacity on the positive electrode active layer thickness was shown to have an extreme character. With increase in the positive electrode active layer thickness the initial section of the increase in the calculated capacity is replaced by a section of a decrease in the capacity. It was found that the process of lithium peroxide molecules’ generation mainly occurs within a narrow region where the pore mouths are in contact with the gas phase. The calculations show that the optimal thickness of the positive electrode active layer is very small (of the order of tens of microns).

A simplified model of lithium–oxygen battery (LOB) discharging is described. Presenting the positive electrode as a monoporous medium characterized by two parameters (porosity and pore radius) allows the study of lithium peroxide formation to be limited to a single pore. A unique aspect of this model is the LOB discharge curve being considered in a broad range of conductivities for a lithium-containing electrolyte. The current density and electrolyte conductivity are considered the core model parameters of LOB discharging. Experimental dependences are investigated for LOB discharge capacity and electrolyte conductivity on the concentration of lithium in an aprotic medium. Based on the results from modeling and experimental data, it is suggested which limiting factors might be responsible for extremely low allowable current densities during LOB discharging.

The active layer of a lithium-oxygen battery (LOB) cathode must have a complex structure consisting of two types of pores (macropores and mesopores). For successful operation of the cathode active layer during the LOB discharge, attempts are being made to create two types of pore clusters: a macropore cluster that provides the transport of oxygen to a zone, where the final product, lithium peroxide, is formed, and a mesopore cluster that guarantees the delivery of lithium ions. The structure of the cathode active layer composed of two types of clusters is optimized in model calculations. However, it from the experimental data, even after the actual implementation of these theoretical recommendations, that the LOB dimensional characteristics during the discharge (in particular, current density I, mA/cm2, and cathodic capacitance C, C/cm2) remain low. In the present work, a new type of cathode active layer structure was suggested: a regular biporous model. In this model, the channels for the supply with oxygen and lithium ions are separated from each other. This fact allows one to simultaneously and independently improve the operation of each of the two channels. The calculations showed a clear advantage of the active layers with this new structure. In particular, the current density i and cathode capacitance С raised to tens of mA/cm2 and about of a thousand of C/cm2.

Currently, the development of lithium–oxygen (air) battery became a hot topic. It is recognised that its specific energy will exceed that of traditional lithium-ion batteries by order of magnitude. The principal element of the lithium–oxygen battery, that is, the active layer of the cathode constitutes a layer of material with a complicated pore structure. During discharge, some electrochemical and chemical processes therein result in the accumulation of lithium peroxide that eventually has been used in the lithium–oxygen battery charging. This power source still suffers from disadvantages, indeed. In this work, computer simulation is used in the elucidating of the effects of the cathode active layer structure on the lithium–oxygen battery overall characteristics during its charging and discharging. A set of obstacles on the way to improvement of the lithium–oxygen battery overall characteristics has been revealed. The obstacles are shown being crucial, they cannot be overcome in terms of current practice of the designing of the lithium–oxygen battery cathode. Therefore, new approaches to the manufacturing of lithium–oxygen battery cathode have to be sought for.

A distinctive feature of discharge of the lithium–oxygen power source (LOPS) with nonaqueous electrolyte is the filling of the positive electrode pores by lithium peroxide that is not soluble in the electrolyte and is characterized by low conductivity. Generally, the cathodic discharge process can be carried out only in a comparatively thin, several tens of micrometers, porous layer bordering on the gas phase. Therefore, the capacity per 1 cm2 of the outer cathode surface proves to be small. In this connection, the problem arises of developing more advanced LOPS and providing efficient performance of the active layers of the positive electrode at an increase in their thickness to achieve higher overall characteristics. In this work, the authors obtain experimental dependences of the positive electrode capacity on the active layer thickness and various current density values. Theoretical analysis of the obtained experimental data is performed. Here, the issues that are of considerable interest of the LOPS discharge theory are discussed.

To perform the oxygen reduction reaction effectively, the active layer of the lithium–oxygen battery positive electrode must have developed surface possessing a complicated pore structure. During discharge (the oxygen reaction cathodic component), the electrode accumulates lithium peroxide, a final product of electrochemical and chemical reactions (resulting in the conjunction of lithium ions, oxygen molecules. and electrons); the latter undergoes oxidation (the oxygen reaction anodic component) during the lithium–oxygen battery charging. The lithium peroxide is a water-insoluble compound that has no electronic conduction; when depositing on the electrode surface it seals openings of narrow pores and prevents oxygen penetration therein. To obtain more lithium peroxide via oxygen reduction in the presence of lithium ions, a cluster of large pores, practically unsealed with the lithium peroxide, is produced in the active layer; the pores supply oxygen deep into the active layer. The Li 2 O 2 accumulation occurs in a cluster of lesser pores with developed surface. In the creating of the lithium–oxygen battery positive electrode active layer optimal structure, the difficulty is that some key quantities are unknown in advance. They are the large-scale and lesser pore average size and their volume fractions in the active layer. To solve the problem, the regular biporous model of the pore structure can be used. In the model, the pore radii are strictly fixed. This opens a relatively easy way for the interconnecting, by calculations, of parameters and the lithium–oxygen battery dimensioning specifications during its discharge. This work aimed at the proposing of the positive electrode active layer regular biporous model and developing of a procedure for the calculating of the lithium–oxygen battery dimensioning specifications during the discharge. it is shown, in a specific context, how the varying of the positive electrode active layer structure and the oxygen consumption constant k can control the Li 2 O 2 accumulation.

The paper deals with a characteristic feature of the discharge process of the cathode of a lithium-oxygen current source (LOCS) with the electrolyte based of a nonaqueous solvent, which is the clogging the positive electrode pores with the insoluble electrolyte and nonconductive reaction product, lithium peroxide Li 2 O 2 . Lithium peroxide is formed in a multistage complex reaction occurring in the course of oxygen reduction. In the reverse process, i.e., anodic LOCS charging, lithium peroxide accumulated in the course of discharge is decomposed with formation of lithium ions, oxygen molecules, and electrons. It is advisable to obtained as much as possible lithium peroxide during the LOCS discharge. However, it “clogs” the cathode pores, prevents the flow of oxygen into them, that, in turn, complicates the further lithium peroxide accumulation. Thus, the calculations show that the cathode discharge process can be mainly carried out only in a relatively thin porous layer bordering on the gas phase. Therefore, in the absence of special measures, the capacity calculated per square centimeter of the outer cathode surface is small. Usually, when the functioning of the active cathode layer is studied, a certain value is assumed for the oxygen consumption that is the main constant of the LOCS charging process (its value is characterized by parameter k). This paper uses computer simulation with variation of k in a wide range. The corresponding variation of the overall characteristics of the LOSC cathode is demonstrated. The causes of the changes in the cathode pores are explained. The study shows that a decrease in constant k (which lead to a decrease in consumption of oxygen intended for formation of Li 2 O 2 ) and an increase in the pore radius (at a transition from micropores to mesopores) result in an increase in the specific cathode capacitance and the amount of lithium peroxide accumulated in the cathode and not in their decrease.

The use of active materials with high resistivity in lithium-ion batteries necessitates covering the surface of active particles with electron-conducting films. If this measure is insufficient, then carbon black is added to the electrode active layer. The ohmic losses are assessed by computer simulation of electrode's active layers with active grains covered by a carbon film. Electrode's active layer is modeled as a set of equal-sized cubic grains of the active material (covered with a conducting film) and the electrolyte; the grains are randomly distributed throughout the active layer. It is shown how the effective conductivity of the active layer decreases in this case. Furthermore, account is taken of the fact that carbon films represent a set of islets, which results in an additional decrease in the effective conductivity of the active layer. By computer simulations in combination with the percolation theory, it is found how the addition of carbon black can increase the conductivity of electrode's active layer.

Full computer simulation of the cathode structure in hydrogen–oxygen fuel cell with polymer electrolyte is performed. Both transport, support grains (agglomerates of carbon particles onto whose surface Pt-catalyst is deposited), and the current generation in active layer are simulated. The active layer operation in potentiostatic mode is studied. The effect of variations of the active layer and the fuel cell temperature (Ts and Т, respectively) on the cathode overall current I and the support grain flooding with water is calculated. The changes in the temperature difference Ts–Т was shown for the first time, experimentally and by the simulation, to generate variations of I and the degree of the support grain flooding with water. In particular, with the increasing of Ts–Т the current I increased, whereas the support grain flooding with water decreased; and vice versa, with the decreasing of Ts–Т the current I drops down, while, the support grain flooding with water grows. An explanation of the phenomena is presented, which takes account of structure of the support grains in which О2 reduction and Н2О generation occur. There exist intrinsic channels for protons and О2 molecules transportation to the catalyst. Water releasing in the support grains is able to fill partially or even entirely the gas pores through which oxygen is supplied to the platinum. As a result, the current generated in the support grains can drop down significantly; at the same time, the value of I also drops down. The degree of the support grainfilling with water is determined by two processes, namely, the flooding and draining. The source of flooding is the current generation; that of draining, the water saturated vapor diffusion and water filtration in nanopores. The lower cathode potential, the higher the flooding rate, whereas the water removal rate grows or drops down with the increasing of decreasing of the temperature difference Тs–Т, respectively. Thus, the temperature difference variations naturally lead to those of the quantity I.

The results of computerized simulation of the process of formation of lithium peroxide attending the discharge of lithium–oxygen power source, in individual pore of constant radius are presented. It is found that, in the model of porous cathode (pores are tortuous, noncrossing, and of the same radius), variation of specific surface of the pores (decrease of pore radius) does not enable a possibility to increase notably the value of specific capacity of the cathode. A necessity of presence of both macropores, and micro- and mesopores in the structure of the active material was discussed. The effect of porous structure of the cathode on the discharge characteristics of LOPS was experimentally demonstrated by the example of some cathode materials (carbon blacks and carbon nanotubes). The highest discharge capacity was achieved with use of the sample of CNT-T NaOH combining pores of various sizes, which corresponds to the formulated hypotheses about an optimal structure of the active cathode material.