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I. INTRODUCTIONHE rechargeable battery industry is experiencing significant growth driven by an upsurge in portable battery-powered devices, electric vehicles and other industrial applications. A number of different battery chemistries, such as lead-acid, nickel-metal-hydride and lithium-ion, among others, are used in these applications. One of the most popular types of rechargeable battery technologies is the lithium-ion battery. Its chemistry provides a high cell voltage, high energy density, long lifespan and exceptional cyclability. All lithiumion battery applications, especially those used in electric Manuscript received April 30, 2015; revised July 20, 2015. This work was supported in part by the Spanish Science and Innovation Ministry and the Regional Ministry of Principality of Asturias under Grants MINECO-13-DPI2013-46541-R, FC-15-GRUPIN14-073 and MINECO-15-TIN2014-56967-R J. C. Álvarez Antón, J. C. Viera, M. González and C. Blanco Viejo are with the Electrical Engineering Department, University of Oviedo, Campus de Viesques, Gijón, Spain 33204 (+34 985-182553; e-mail: anton@uniovi.es).P. J. Garcia Nieto and E. García Gonzalo are with the Mathematics Department, University of Oviedo, Spain 33007 (e-mail: pjgarcia@uniovi.es).vehicles, require a Battery Management System (BMS). The main objective of a BMS is to maintain the health of all the cells in the battery within the manufacturer's recommended operating conditions in order to prolong the lifespan of the battery pack. One of the most important BMS functional requirements is that of estimating the State-of-Charge (SoC) of the battery or of the individual cells in the battery pack. SoC is an expression of the current battery capacity as a percentage of its maximum capacity. The BMS needs to estimate the SoC in order to report the capacity left in the battery, typically called the "gas gauge". Several applications require accurate measurement of SoC to give users an indication of available runtime. The SoC is also needed to control the battery charging or discharging process. This control can avoid situations such as over-discharging or overcharging, which lead to premature wear-out of the battery. The lithium-ion chemistry operates safely within the designed operating voltages; however, the battery becomes unstable and may pose a safety hazard if overcharged. Over-charging stresses the battery and may lead to damage. Over-discharging also stresses the battery and reduces its lifespan.The available capacity of a battery depends on several factors such as cell chemistry, charging rates, discharging rates and temperature. All of these factors need to be considered when calculating the SoC. Many methods for estimating the SoC have been reported in the literature [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20]. For instance, measuring cell voltage to calculate the SoC can work well for lead-acid battery chemistries, for which the cell voltage and SoC are fairly linearly related, but is ineffective for lithium-ion, for which the volta...

Abstract:The cell case temperature versus time profiles of a multistage fast charging technique (4C-1C-constant voltage (CV))/fast discharge (4C) in a 2.3 Ah cylindrical lithium-ion cell are analyzed using a thermal model. Heat generation is dominated by the irreversible component associated with cell overpotential, although evidence of the reversible component is also observed, associated with the heat related to entropy from the electrode reactions. The final charging stages (i.e., 1C-CV) significantly reduce heat generation and cell temperature during charge, resulting in a thermally safe charging protocol. Cell heat capacity was determined from cell-specific heats and the cell materials' thickness. The model adjustment of the experimental data during the 2 min resting period between discharge and charge allowed us to calculate both the time constant of the relaxation process and the cell thermal resistance. The obtained values of these thermal parameters used in the proposed model are almost equal to those found in the literature for the same cell model, which suggests that the proposed model is suitable for its implementation in thermal management systems.

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