Discharge Oxide Storage Capacity and Voltage Loss in Li-Air Battery

Abstract

Air cathodes, where oxygen reacts with Li ions and electrons with discharge oxide stored in their pore structure, are often considered as the most challenging component in nonaqueous Lithium-air batteries. In non-aqueous electrolytes, discharge oxides are usually insoluble and hence precipitate at local reaction site, raising the oxygen transport resistance in the pore network. Due to their low electric conductivity, their presence causes electrode passivation. This study aims to investigate the air cathode's performance through analytically obtaining oxygen profiles, modeling electrode passivation, evaluating the transport polarization raised by discharge oxide precipitate, and developing analytical formulas for insoluble Li oxides storage capacity. The variations of cathode quantities, including oxygen content and temperature, are evaluated and related to a single dimensionless parameterthe Damköhler Number (Da). An approximate model is developed to predict discharge voltage loss, along with validation against two sets of experimental data. Air cathode properties, including tortuosity, surface coverage factor and the Da number, and their effects on the cathode's capacity of storing Li oxides are formulated and discussed.

Capacity loss of non-aqueous Li-Air battery due to insoluble product formation: Approximate solution and experimental validation

“…The analytical formula are targeted at the effects of insoluble Li oxides, which is less related to electrolyte selection and decomposition. Table 2 MacMullin number (N M ) of a system consisting of a dispersed non-conducting phase in a conductive medium [36].…”

Discharge Precipitate's Impact in Li-Air Battery: Comparison of Experiment and Model Predictions

“…As discharge proceeds, precipitate accumulates, narrowing the pore network and thus increasing oxygen transport resistance and associated voltage loss. In the present cathode, this voltage loss is anticipated to be unimportant, which can be justified by evaluating the Damköhler number (Da): 9…”

“…7,8 Because the precipitates are physically deposited inside the cathode electrode, the electrode structure, including porosity, carbon particle morphology, and tortuosity, greatly influence the voltage loss due to the precipitate accumulation. 9 Xiao et al 10 investigated the impacts of carbon microstructure and loading, and found that the cathode capacity increases with the carbon material's mesopore volume. Zhang et al 11 employed galvanostatic discharge, polarization, and AC-impedance techniques, showing that the discharge performance is determined mainly by air cathodes.…”

“…16,20,23 Studies showed precipitate deposits may reach 1-10 μm in their size. 9,28,29 In physical modeling, precipitate's impacts need to be accounted for as one major mechanism of voltage loss. Direct observation of film formation at planar surfaces indicated a film resistor model is suitable to describe associated voltage loss.…”

A Simple Model for Interpreting the Reaction–Diffusion Characteristics of Li-Air Batteries

“…[17][18][19][20][21][22] These models frequently predict pore clogging at the gas-electrolyte interface such that much of the interior electrode area becomes inactive. Some work has focused on discharge capacity limits caused by electronically insulating Li 2 O 2 23,24 and other work has addressed the impact of oxygen and ion diffusivity as a function of porous electrode structure 18,25 and electrolyte properties.…”