Lithium Ion Battery Classification And Future Trend（1）

The global economy is experiencing a transition from carbon-intensive energy resources to low-carbon energy resources. Electric vehicles are being placed an essential priority by most countries due to the comparative advantage in terms of carbon emission over internal combustion engine vehicles (Wu et al., 2012). According to the 2019 IEA Global Electric Vehicle Outlook, the global stock of electric passenger cars is above 5.1million in 2018, compared with the global stock of 0.39 million in 2013, the growth rate is around 242%. The sales and stock of electric vehicles will likely continue to increase further because of government incentive policies and the cost decline of electric vehicles. In the New Policies Scenario of the 2019 IEA outlook, it is projected that the global stock of electric vehicles can exceed 130 million in 2030, excluding two/three-wheelers (IEA, 2019).
On the other hand, there are various challenges to make electric vehicles attractive to users. The more important aspects which influence the adoption of electric vehicles as a kind of transportation instead of internal combustion engine vehicles are their driving distance and higher cost. Battery applied in electric vehicles is a critical determinative factor in driving distance and the cost of vehicles. These days, lithium-ion batteries are the most favorable electrochemical energy storage system for electric vehicles due to their high energy density, excellent self-discharging rate, high operation voltage, long cycle life, and no memory effect (Panchal et al., 2018). To overall understand the development process and technology trend of electric vehicles with respect to the battery, this paper will focus on talking about the Structure of lithium-ion batteries, classification of lithium-ion battery and comparison between different lithium-ion battery chemistries.

Structure of lithium ion battery

The lithium-ion battery is a kind of rechargeable battery, also called for "rocking chair battery", in the charged condition, the anode includes a high level of intercalated lithium while the cathode lacks lithium, lithium ions move through an electrolyte to accomplish from the negative electrode to the positive electrode during discharging, return when charging. The lithium-ion battery is comprised of three major parts: anode, cathode, and electrolyte. The anode and cathode are connected electrically but separated physically by the electrolyte(Daniel, 2008)
Figure 1: The smallest unit structure of lithium-ion battery (Lee et al., 2014)

Classification of lithium ion battery

The anode of lithium-ion battery is typically comprised of graphite, the electrolyte is typically made of organic carbonate solvents involved in dissolved lithium salts (often LiPF6), and the cathode varies in different chemical compositions. According to the cathode chemistry composition, lithium-ion battery which is mainly used to power electric vehicles include lithium iron phosphate（LFP）, lithium nickel cobalt aluminum oxide（NCA）, lithium nickel manganese cobalt oxide（NCM）lithium manganese oxide（LMO）and Lithium tantalite oxide (LTO). The comparison between different lithium-ion battery chemistries is shown in sheet 1. Moreover, lithium-ion battery which can power electric vehicles has typically had three types of form: cylinder, pouch, and prismatic (See figure 2).

Figure 2: Different form of lithium ion battery

                   Cylinder                                                 Prismatic                                                                      Pouch

Cylindrical battery and prismatic battery both are with outer solid and metal shell. Prismatic battery for electric vehicles primarily delivers in the format of the high capacity, and this offers a simple assembly procedure of battery system. But the prismatic battery allows flexible design (TWAICE, 2019), this leads to the various sizes of prismatic battery, in other words, this means the instability of production because of frequently adjusting production lines for different sizes of battery. A major advantage of cylindrical cells is the long experience in the production of cylindrical design, the small cylindrical cells are made in very high volumes by automated manufacturing and the price is less expensive than prismatic and pouch for standard shapes, but the small size of cylindrical battery exists weakness of high difficulty and risk of battery system integration, especially complicated assembly process, and cooling system as well as the monitoring effort required during operation (Ampow Blog, 2019). Compared with a prismatic battery and cylindrical battery, a pouch battery is enclosed by a flexible, mostly aluminum-based outer foil. It allows flexible design which is the same as the prismatic battery, pouch battery not only is light and cost-effective but also the pouch shell allows the most efficient use of space and is able to package efficiency of 90–95%. But expanding after some cycles is the primary issue (Ampow Blog, 2019).