On-board aging estimation using half-cell voltage curves for LiFePO4 cathode-based lithium-ion batteries for EV applications

Article

Abstract

The aim of this work is the design of an algorithm for on-board determination of the actual capacity of a lithium iron phosphate (LFP) cathode-based lithium-ion battery for electric vehicle applications. The presented approach is based on the detection of the predominant aging mechanisms (in terms of loss of lithium and loss of active material in both electrodes) by determining the single electrode voltage curves. The information related to the characteristic length and position of the voltage plateaus, which can be gathered during battery operation, can be used to obtain the actual aging state of the cells. The length of the plateaus depends on the respective position that the voltage curves of the single electrodes have in relation to each other. Relating the change of the plateau characteristics to the possible aging mechanisms allows the determination of the actual battery aging state in terms of total cell capacity. The work presents a possible implementation of an algorithm for capacity determination based on the described methodology. The algorithm is validated with various differently aged LFP cells. Furthermore, the work discusses the ability of the method to detect the actual battery capacity if the characteristics of only part of the quasi-OCV (open circuit voltage) curve are detected. Achieved accuracy and existing limitations are described and discussed in detail.

Key words

LiFePO4 cells On-board capacity estimation Aging mechanisms Single electrode voltage curves 

Nomenclature

BMS

battery management system

DVA

differential voltage analysis

EV

electric vehicle

ICA

incremental capacity analysis

LAM

loss of active material

LFP/LiFePO4

lithium iron phosphate

LLI

loss of lithium inventory

OCV

open circuit voltage

PHEV

plug-in hybrid electric Vehicle

SEI

solid electrolyte interface

SoC

state-of-charge

SoH

state-of-health

Subscripts

a

anode

BOL

begin-of-life

c

cathode

EOL

end-of-life

Ne

negative electrode

Pe

positive electrode

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Copyright information

© The Korean Society of Automotive Engineers and Springer-Verlag Berlin Heidelberg 2016

Authors and Affiliations

  1. 1.Electrochemical Energy Conversion and Storage Systems Group, Institute for Power Electronics and Electrical Drives (ISEA)RWTH Aachen UniversityAachenGermany
  2. 2.Institute for Power Generation and Storage Systems (PGS), E.ON ERCRWTH Aachen UniversityAachenGermany
  3. 3.Jülich Aachen Research AllianceJARA-EnergyAachenGermany

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