Li-ion Polymer Cells

Cai W, Wang H, Maleki H, Howard J, Lara-Curzio E (2011) Experimental simulation of internal short circuit in Li-ion and Li-ion-polymer cells. J Power Soiffces l%(18) 7779-7783... 

A related Li ion cell type is the Li ion polymer cell that uses a polymer gel electrolyte. Li ion polymer cells are often designed as flat prismatic cells and can be made quite thin. 

The Li-ion polymer cells are enclosed in a soft-case to reduce the overall size and weight and have approximate dimensions of 3.9 inches in length, 1.6 inches in width, and 0.23 inches in thickness. The ceU is constmcted by winding long strips of electrodes into a jeUy roU configuration, which is then enclosed in a polymer-coated aluminum pouch with heat-sealed seams (see Fig. 2.7). There were 144 cells in each carton, as shown in Fig. 2.8. Each of those cartons contained two smaller cartons of 72 cells. 

Fig. 2.8 Li-ion polymer cells in cartons on a pallet (courtesy of FM Global)...

The Li-ion polymer cells exhibited an initial fire development similar to the Class 2 commodity until 110 s when the fire size began to decline due to the consumption of the cartoned material. The fire size steadily declined until 305 s when the Li-ion cells became significantly involved, and the fire reached a maximum of 3,800 kW at 750 s. 

Wang, C.-W. and A. M. Sastry. Mesoscale modeling of a li-ion polymer cell. Journal of the Electrochemical Society 154(11) A1035-A1047, 2007. 

Peramunage and Abraham have recently reported an advanced lithium-ion polymer cell [106, 107]. In this case, a material of the Li [Lij/3Tij/3]04 family [108, 109], e.g., the Li4Ti50i2, intercalation compound, has been used as an anode. The lithium intercalation-deintercalation process in this compound is shown in Equation 7.14. 

Tabie 1.1 Advantages and disadvantages of Li-ion and Li-ion polymer rechargeable cells... 

Added advantages and disadvantages of Li-Ion polymer/laminate cells ... 

Safety is a key issue for Li-Ion batteries. The U.S. Department of Transportation (DOT) and the United Nations classify Li-Ion and Li-Ion polymer batteries as hazardous materials for shipping. The DOT grants exemptions for shipping small Li-Ion cells, provided that the cells/battery with limited lithium-equivalent content... 

Contestabile, M. Morselli, M. Paraventi, R. Neat, R. J. A comparative study on the effect of electrolyte/additives on the performance of ICP383562 Li-ion polymer (soft-pack) cells, J. Power Sources 2003,119-121, 943-947. 

Initially, Li batteries used a liquid electrolyte, necessitating the use of a robust case for safety. It is now used in the ionized form. Figure 23.7 shows a typical Li ion cell utilizing a Li20 cathode and a carbon compound anode separated by a microporous membrane, using a non-aqueous electrolyte such as a Li salt dispersed in a mixture of alkyl carbonates. Since the non-aqueous electrolytes can be flammable. Valence Technology has developed the Li ion polymer battery using liquid lithium ion electrochemistry in a matrix of conductive polymers that eliminate free electrolyte within the cell. 

Li-ion polymer and flat plate cells are produced in small sizes for cellular phones (about 0.5 Ah and higher) and large sizes (up to 200 Ah) for energy storage and motive power applications. A commOTi characteristic is that the polymer separator holds the electrolyte and forms a physical barrier between the anode and cathode to prevent internal shorting. Most polymer cells are flat plate (prismatic) construction. 

Also launched in late 2010, the Chevrolet Volt uses a 16 kWh battery based on LG Chem s lithium-ion polymer cells. The Volt is an EREV, which means that the vehicle has both a 1.4-1 ICE and a 16 kWh Li-ion battery pack. The ICE acts as a generator operating the motors once the battery charge has dropped to a minimum level determined by the system controller. This combination of Li-ion battery and ICE allows the vehicle a total range comparable to a standard ICE. 

Based on the range of Li-ion cell types, 18,650 format cylindrical Li-ion batteries, prismatic Li-ion polymer batteries of comparable capacity to the test 18,650 cells, and packaged power tool rechargeable battery packs with cylindrical cells were identihed as the most pertinent for the analysis. These batteries are typically found in a host of different commodities, including, portable GPS devices, portable game players, portable DVD players, portable televisions, portable radios, cellular phones, music players, electronic readers, notebook computers, cordless headphones, universal remote controls, cameras, camcorders, two-way radios, rechargeable vacuums, electric razors, electric toothbrushes, and electric vehicles. 

The time of battery involvement was also estimated by FM Global earlier in the fire development. During the Li-ion cylindrical cell and polymer cell tests, the convective heat release rate steadily decreased after the initial vertical flame spread along the cartoned commodity packaging to approximately 600 kW at 200 and 305 s, respectively. The heat release rate then steadily increased to the upper threshold value of 1,250 kW. In both tests, the wood pallets on the second tier... 

Figure 20. Construction of (A) cylindrical, (B) prismatic, and (C) polymer Li ion cells. (Reprinted with permission from a brochure by Sony Corporation).

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