Mechanism and influencing factors of lithium-ion batteries

Mechanism and influencing factors of lithium-ion batteries

Abstract This chapter introduces the operating mechanism, influencing factors, key indica tors, and some mainstream state estimation methods of lithium-ion batteries. First, understanding the main composition and internal working principle of lithium-ion batteries is the prerequisite and basis for other work. Second, internal resistance, open-circuit voltage (OCV), terminal voltage, current thermal energy, capacity variation, and temperature characteristics are the main features of the battery, which can be further used to accurately characterize the battery state. The state of charge, state of health, state of power, depth of discharge, and cyclic life are the key indicators of state estimation, while the discharging test, Ampere-hour integral, OCV, internal resistance, and Kalman filtering are basic state estimation strategies. Based on the Kalman filter, there are many improved algorithms, such as the unscented Kalman filter and adaptive Kalman filter, which have achieved good application effects. Besides, other algorithms such as neural networks, support vector machines, and some improvement strategies are also introduced. The advancement of these algorithms has made an important contribution to improving the whole-life-cycle state estimation effect of lithium-ion batteries. Keywords: Operating mechanism; Battery characteristics; Influencing factor; State of charge; State estimation; Kalman filtering; Cyclic life; Temperature; Open-circuit voltage 2.1 Introduction With the development of society, the shortage of primary energy and increasing atten tion to environmental pollution have promoted the rapid growth of lithium-ion batteries. The invention of new energy and environmental protection are important research topics, and the fact that lithium-ion batteries are relatively environmentally friendly in use has explained the gradual replacement of other relatively polluting batteries. To improve the function of electronic equipment, especially electric vehicles, hybrid electric vehicles, smart grids, and UAVs that all use lithium-ion batteries [39]. The research on lithium-ion batteries and their related parameterization is of global importance. There are several journals and periodicals with published articles and projects on several important theories and ideas related to lithium-ion batteries and their parameter estimation, and the number is increasing daily [40]. According to the global lithium-ion battery market, it has been growing at a compound annual growth rate of 10.6% since 2016 and is estimated to reach $56 billion by the year 2024, which means that the demand for lithium-ion batteries is set to be more than double by this year. This implies that the increasing demand would lead to more improve ments and has a lot of broad prospects for more research in the field, as shown in Figure 2.1. The battery model studies the relationship between the external characteristics and the internal state of the battery by establishing a mathematical model. Discrete time and state-space forms are also used for the state of charge (SOC) estimation. The present literature makes mention of electrical equivalent circuit (EEC) models as being widely used as a foundation for model-based estimation and control [41,42]. Generally, the equivalent circuit models are selected for the lithium-ion battery modeling, including the Rint model, Thevenin model, RC model, and PNGV model [43,44]. These models use RC loops of different orders to model the polarization characteristics of batteries [45]. Among them, the Thevenin model is widely used, but as all its components may change with the state of the battery, its accuracy is not high [46]. For more accurate parameter identification [47,48], a new design using charge–discharge is being developed, and SOC estimation methods are combined [49,50] as a means of estimating SOC in the presence of unknown or time-varying battery parameters. Research in this field either assumes the available precise SOC–OCV [51,52] or a constant during discharge. The RC parameters are deter mined by analyzing the transient state of the battery voltage response [25] under certain excitations, such as constant current or pulse current experiments. The voltage source in an EEC typically represents the open-circuit voltage (OCV), which depends on the SOC [53]. The relationship between SOC and OCV can be 2015 2016 2017 2018 2019 CAGR 10.6% (2016–2024) 2020 2021 2022 2023 2024 56 Figure 2.1 Global lithium-ion battery market size and forecast 12 Battery state estimation: methods and models identified by charging or discharging the battery with a small current. Parameter identification based on current–voltage data is addressed [48] by a method that simplifies the problem of solving a set of high-order polynomial equations to solving several linear equations and a single variable polynomial equation. 2.2 Operating mechanism In the global high-tech growth, the lithium-ion battery industry is an excellent direction. The benefits of lithium-ion batteries are high capacity, high conversion rate, long lifespan, and no emission. Because of its good electrochemical durability, high fuel density, long service life, and no maintenance, it is often used in electric vehicles and various power storage systems. Lithium-ion batteries have been widely used at present. It primarily encompasses five fields, including transporta tion, power storage, mobile communication, modern energy storage, and military aerospace. It will substitute oil with electricity, minimize emissions of greenhouse gas, and store electricity in the power grid in the unnecessary conditions of electric vehicles. 2.2.1 Brief introduction The battery converts chemical energy into electric energy, which is irreversible in the primary battery and rechargeable in the secondary battery. Lithium-ion batteries can be divided into three different categories, such as lithium metal, lithium-ion, and lithium-ion polymer. Lithium metal batteries are primary batteries, while lithium-ion and lithium-ion polymer batteries are both rechargeables. The lithium-ion battery system is a complex system that integrates chemical, electrical, and mechanical characteristics, so various characteristics must be considered in the design. In parti cular, the safety and life attenuation characteristics contained in the chemical char acteristics of the battery cell cannot be directly evaluated, nor can they be easily predicted in a short time. Therefore, the battery technology, group technology, and battery management system (BMS) technology should be implemented when designing a battery system, as well as battery protection. Consequently, the reliability and lifespan of the battery should be considered. The lithium-ion battery is an advanced battery technology that uses lithium ions as the key component of its electrochemical reaction. During the discharge cycle, lithium atoms in the anode are ionized and separated from their electrons. The lithium ions are small enough to pass through the micro-permeable separator between the anode and the cathode. This separator recombines with its electrons and is neutralized electrically. A class of organic compounds known as ether is used as the electrolyte of lithium-ion batteries. The most common combination of materials called electrodes is that of lithium cobalt oxide (cathode) and graphite (anode), which is most commonly found in portable electronic devices such as cellphones and laptops. Other cathode materials include lithium manganese oxide and lithium iron phosphate. Lithium manganese oxide is commonly used in hybrid and electric vehicles. Due to the small size of lithium ions, the batteries can have a Mechanism and influencing factors of lithium-ion batteries 13 very high voltage and charge storage per unit mass and unit volume. Lithium is the lightest of all metals, which has the greatest electrochemical potential and provides the largest specific energy per weight. Rechargeable batteries with lithium metal on the anode provide extraordinarily high energy densities. Lithium-ion batteries are facing competition from numerous alternative battery technologies, most of which are in the development stage [54]. One such alternative called a saltwater drive battery is developed by the energy equation. They are com posed of saltwater, manganese oxide, and cotton, which are made by using abundant, non-toxic materials, and modern low-cost manufacturing techniques [55]. Because of this, they are the only cradle-to-cradle-certified battery in the world. The batteries mentioned in it are all lithium-ion batteries. The cathode substrate of a lithium-ion battery is lithium-alloy metal oxide [56]. Its negative electrode component is gra phite. The essence of charge and discharge is the electrochemical reaction in lithium ion batteries. The essential response and working process of lithium-ion batteries are shown in Figure 2.2. Figure 2.2 shows that the lithium-ion metal oxide positive electrode material is emitted during the battery charging phase [57]. The lithium cobalt metal oxide is transferred through the electrolyte and the separator, and the carbon substrate is incorporated into the negative electrode-coated frame. The positive electrode enters a state of prosperity rich in lithium-ion at this stage. On the contrary, the negative elec trode enters a lithium-ion lean state [58]. During the discharge process, lithium-ion can Septum Electrolyte Electrolyte Load Power Shell e e- + - Charge Discharge Positive electrode Negative electrode Li+ CoO2 C Figure 2.2 Schematic structure of a lithium-ion battery

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