Numerical analysis of lead-acid AGM battery discharge characteristics

Abstract

Chemical current sources are an integral part of vehicles, many types of aircraft, and stationary power systems. The current state of chemical current sources encompasses a wide range of problems, whose solution is based on many fields of knowledge. At the same time, experimental studies remain extremely labor-intensive. The diversity of devices and modern technologies requires adequate, qualified solutions. One of the research lines ensuring the development and performance control of batteries is the construction of equivalent electrical circuits, which make it possible to obtain sufficiently accurate answers. Another, classical, approach is based on the electrochemical laws governing the behavior of heterogeneous systems in an active ionized medium. In this work, based on familiar equations of ion exchange in electrolytes in the presence of electrochemical reactions on the electrode surfaces, the AGM-type traction battery discharge process is simulated mathematically. The mathematical model takes into account the main design and physicochemical features of this battery type. The equations are solved numerically using an explicit 2D finite-difference scheme. As a result, discharge characteristics are obtained at various current values and separator plate thicknesses. A strong effect of the current magnitude on the behavior of the discharge characteristic is noted. The obtained values are evaluated based on known experimental data and theoretical relationships. It is shown that at relatively small currents, the found values of the discharge process time and the current magnitudes obey the known relationship. The modern equivalent circuit theory allows a discharge curve to be obtained to a good of accuracy, thus making a comparison with it quite correct. Thus, the estimated discharge time obtained by numerically solving the complete system of equations describing mass transfer in an electrochemical cell of the battery is quite close to the theoretical relationship. Furthermore, in a certain range of values, it is also close to the published data of other authors for real operating batteries of this type. This indicates the promisingness of further deepening and developing the mathematical model based on physicochemical laws to provide a deeper insight into the process and the behavior of various parameters and components associated with it. Hence, the scientific novelty of this work lies in the mathematical formalization of the operation of a complex electrochemical system with certain technological and design features. Its practical value lies in the possibility of simulating and calculating the parameters of modern current sources. This is important both for newly created types of chemical current sources and for controlling the operation and determining the state of batteries of this type currently in operation.