Analysis of Degradation Mechanism of Lithium Iron Phosphate Battery

Genki Kaneko,Yasuhiro Daisho,Koichiro Taniguchi,Shoichi Inami,Yushi Kamiya,Toshio Hirota,Soichiro Inoue

doi:10.3390/wevj6030555

Genki Kaneko, Yasuhiro Daisho + Show 5 more

Open Access

https://doi.org/10.3390/wevj6030555

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Abstract

The degradation mechanisms of lithium iron phosphate battery have been analyzed with 150 day calendar capacity loss tests and 3,000 cycle capacity loss tests to identify the operation method to maximize the battery life for electric vehicles. Both test results indicated that capacity loss increased under higher temperature and SOC conditions. And also, large increase of internal resistance on the high temperature and high SOC conditions was confirmed by AC impedance tests. The real cycle capacity loss characteristic was derived by subtracting the capacity decrease due to calendar capacity loss during the cycle test from the overall capacity loss characteristic obtained from the cycle test. As a result, it is found that the real capacity loss contains not only structural disorders of electrode but also degradation factors due to the chemical reactions. Characteristics of degradation were quantified with equations based on the chemical kinetics. With this degradation prediction, an operation method was proposed that is compatible with the long life of batteries and the safety driving of a vehicle. As a result, with optimizing the SOC range used in the operation as follows: 30-10% in the warm seasons, 45-25% in the cold seasons, it was found that batteries can last 4 times longer than it used with high SOC range in every season.

Highlights

In recent years, battery electric vehicles (BEVs) have been actively developed and introduced to the market
These results indicated that the capacity loss increased under the higher temperature and state of charge (SOC) conditions
It is thought that the main cause of this large capacity loss is that the reactions between the lithium ion and the electrolyte are accelerated under high temperature and SOC conditions

Summary

Introduction

Battery electric vehicles (BEVs) have been actively developed and introduced to the market. In terms of more popularization of BEVs, weaknesses for cruising range, cost of batteries and user-friendliness of charging remain major challenges. To resolve these issues, a concept “short range driving and very frequent charging” was formulated [1]. A concept “short range driving and very frequent charging” was formulated [1] Under this approach, the authors developed the short-range frequent-recharging electric vehicles (Figure 1) and studied methods of greatly reducing the number of large, heavy, and expensive batteries. By analyzing the degradation mechanism of batteries, it could be possible to EVS27 International Battery, Hybrid and Fuel Cell Electric Vehicle Symposium obtain guiding principles for generation batteries and indicate how to last the life of batteries. The aim of this paper is to contribute the longevity of BEVs with addressing the operation method to realize the coexistence vehicle’s safety operation and battery’s long life

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