IMECE 2018-86582 LOW-TEMPERATURE ENERGY EFFICIENCY OF LITHIUM-ION BATTERIES

In this study, the low-temperature energy efficiency of lithium-ion batteries (LIBs) with different chemistries and nominal capacities at various charge and discharge rates is studied through multi-physics modeling and computer simulation. The model is based on the irreversible heat generation in the battery, leading to the charge/discharge efficiency in LIBs with graphite/LiFePO4, graphite/LiMn2O4, and graphite/LiCoO2 electrode materials in which the effects of the battery nominal capacity at various charge and discharge rates are studied. Using characterized sources of the heat generation in the LIB leads to providing a battery efficiency plot at different operation condition for each LIBs. The results of this study assist the battery engineers to have much more accurate prediction over the efficiency of the LIBs at low temperatures. INTRODUCTION Lithium-ion batteries (LIBs) possess several features that made them the most popular type of rechargeable electrical energy storage system in market [1]. High operating voltage, high energy & power, good cycling performance, low selfdischarge and no memory effect made these batteries suitable for many applications including portable electronic [2]. Generally, a LIB is shaped of two electrodes (anode and cathode) that are usually mechanically supported by metallic current collectors as well as the electrolyte that allows lithium-ion transfer between electrodes which the behavior is characterized 1 Corresponding Author (sfarhad@uakron.edu) based on the theory of the operation of porous electrodes developed by Newman [3]. In LIBs, Li-ions transport from one electrode to the other, while at the same time allowing electrons flow through an external circuit connected to the battery [4]. The anode and cathode are electrically insulated from one another by a polymer separator, which is permeable to Li-ions but not to electrons. Since LIBs are being used in wide range of operation temperature, with regard to the cold season in North America, they should be designated optimally to maintain the desired performance at low temperatures. From the basic characteristics of large-scale LIBs, particularly those used as energy storage devices in grid systems and EVs, such as voltage, current, and capacity, more comprehensive analysis requires concerning the macroscopic properties of LIB such as energy efficiency at low temperatures. Accordingly, energy efficiency plays key role in evaluating the working conditions of LIBs and represents the utilization of chemical energy stored in LIB at discharge or the utilization of electrical energy toward storing chemical energy in LIB at charge [5]. Also, the considerable importance of LIB’s performance, leads a large number of researcher to conduct study in this field and provide new approach to assist this topic [6-13]. The goal of this study is to calculate the LIB energy efficiency at charge/discharge, using electrochemistry and electrical theory. Since the amount of electrochemical energy (EE) at discharge and the amount of electrical energy (E) dissipated at charge, change to heat, the irreversible heat generation is calculated to predict the LIB energy efficiency at charge/discharge. Studies on