Open Access
Fast capacity and internal resistance estimation method for second-life batteries from electric vehicles
(Elsevier, 2023) Braco Sola, Elisa; San Martín Biurrun, Idoia; Sanchis Gúrpide, Pablo; Ursúa Rubio, Alfredo; Ingeniería Eléctrica, Electrónica y de Comunicación; Institute of Smart Cities - ISC; Ingeniaritza Elektrikoa, Elektronikoaren eta Telekomunikazio Ingeniaritzaren; Universidad Pública de Navarra / Nafarroako Unibertsitate Publikoa
The success of second-life (SL) Li-ion batteries from electric vehicles is still conditioned by their technical and economic viability. The knowledge of the internal parameters of retired batteries at the repurposing stage is key to ensure their adequate operation and to enlarge SL lifetime. However, traditional characterization methods require long testing times and specific equipment, which result in high costs that may jeopardize the economic viability of SL. In the seek of optimizing the repurposing stage, this contribution proposes a novel fast characterization method that allows to estimate capacity and internal resistance at various state of charge for reused cells, modules and battery packs. Three estimation models are proposed. The first of them is based on measurements of AC resistance, the second on DC resistance and the third combines both resistance types. These models are validated in 506 cells, 203 modules and 3 battery packs from different Nissan Leaf vehicles. The results achieved are satisfactory, with mean absolute percentage errors (MAPE) below 2.5% at cell and module level in capacity prediction and lower than 2.4% in resistance estimation. Considering battery pack level, MAPE is below 4.2% and 1.8% in capacity and resistance estimation respectively. With the proposed method, testing times are reduced from more than one day to 2 min per cell, while energy consumption is lowered from 1.4 kWh to 1 Wh. In short, this study contributes to the reduction of repurposing procedures and costs, and ultimately to the success of SL batteries business model.
Open Access
Experimental assessment of cycling ageing of lithium-ion second-life batteries from electric vehicles
(Elsevier, 2020) Braco Sola, Elisa; San Martín Biurrun, Idoia; Berrueta Irigoyen, Alberto; Sanchis Gúrpide, Pablo; Ursúa Rubio, Alfredo; Ingeniaritza Elektrikoa, Elektronikoaren eta Telekomunikazio Ingeniaritzaren; Institute of Smart Cities - ISC; Ingeniería Eléctrica, Electrónica y de Comunicación; Gobierno de Navarra / Nafarroako Gobernua, 0011–1411–2018–000029 GERA; Universidad Pública de Navarra / Nafarroako Unibertsitate Publikoa, ReBMS PJUPNA1904
The reutilization of batteries from electric vehicles allows to benefit from their remaining energy capacity and to increase their lifespan. The applications considered for the second life of these batteries are less demanding than electric vehicles regarding power and energy density. However, there is still some uncertainty regarding the technical and economic viability of these systems. In this context, the study of the ageing and lifetime of reused batteries is key to contribute to their development. This paper assesses the experimental cycle ageing of lithium-ion modules from different Nissan Leaf through accelerated cycling tests on their second life. The evolution of the internal parameters during ageing and the correlation between them are shown, including the analysis of best fitting curves. In addition, a second-life end-of-life criterion is proposed, based on capacity and internal resistance measurements during cells ageing, which can be applied to real application in order to prevent safety issues. By estimating future values from degradation trends and checking latter measurements, the ageing knee is identified. Results show that the modules operate for at least 2033 equivalent full cycles before reaching their ageing knee. This would mean more than 5 years of operation in a real second-life application, such as a photovoltaic self-consumption installation with daily cycling. Moreover, it is shown that a traditional cell characterisation based on capacity and internal resistance measurements is not enough to predict the durability of a cell during its second life.

San Martín Biurrun, Idoia

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