An SOE estimation model considering electrothermal effect for LiFePO₄/C battery

Abstract

Summary The state of energy (SOE) is an important performance parameter and evaluation index for LiFePO4/C battery since the available energy can be known more intuitively through SOE compared with state of charge (SOC). First, in order to improve the estimation accuracy of SOE, a novel estimation model combining electrical energy and thermal energy is put forward by studying the effects of discharge rate to the change laws of all kinds of energy inside the battery cell. Moreover, the concepts of unavailable energy Eu, maximum allowable energy E, and discharge energy efficiency η are originally proposed based on the analysis of energy consumption. Second, the parameter of actual maximum energy and energy consumption revised by the case of LiFePO4/C battery can give an example to show the specific steps for improving the estimation accuracy of SOE during any integration time by using the novel SOE estimation model. Lastly, 2 international standard test experiments of EV are conducted to show the correction of SOC can efficiently limit the error below 4.6% and also indicate the novel SOE estimation method suitable for application area.

Nonuniform current distribution within parallel-connected batteries

“…Lithium-ion batteries with high capacity are critical for progressing electrification of mobility and grid energy storage, which would enable a sustainable energy future. 1,2 The parallel batteries can increase the whole capacity and meet the requirements of power. 3 What is more, the parallel connections can increase the reliability of the battery system.…”

A high-performance composite positive electrode based on graphene and Li (Ni1/3Co1/3Mn1/3)O2

“…However, development of new cathode electrodes with higher energy densities with improved stability is still needed for enhanced devices . The most important commercial cathode electrodes and their properties are given in Table …”

“…Layered LiMO 2 (M = Ni, Fe, Co, Mn, or mixture), olivine LiMPO 4 , or spinel LiMn 2 O 4 ‐based cathodes are commonly used for Li ion batteries . Among these cathode materials, LiNi 1/3 Mn 1/3 Co 1/3 O 2 (NMC) is the most promising cathode due to its lower cost, lesser toxicity, and better stability during cycling even at high temperature .…”

A graphical model for evaluating the status of series-connected lithium-ion battery pack

“…The relationship between the cells and the battery pack should be built by mathematical formulae as simple as possible, especially for those states that are critical for battery management. The common states that can reflect the cell variations include the cell capacity, the state of charge (SOC), and the state of energy . However, the state of battery pack cannot be calculated by algebraic equations that describe the states of single cells.…”

“…The common states that can reflect the cell variations include the cell capacity, 25 the state of charge (SOC), 26 and the state of energy. 27 However, the state of battery pack cannot be calculated by algebraic equations that describe the states of single cells. A well-acknowledged equation that defines the SOC and capacity of the battery pack was proposed by Lu et al 28 The capacity of the battery pack is defined as the sum of the working capacity of two specific cells.…”