Method and system for assessing a state of charge/discharge (SOC/SOD) for an electrochemical cell

A method for assessing a state of discharge (SOD) for a cell comprising a primary electrochemical cell, the cell having an operational mode during which the cell is discharged into a load and a rest mode, the method comprising the steps of:

• measuring voltage, current and temperature of the cell in a course of the operational mode and during the rest mode,
• calculating entropy variation (ΔS) data, enthalpy variation (ΔH) data, Open-Circuit voltage (OCV) data and state of discharge (SOD) data, from the voltage, current and temperature measurements,
• determining parameters α′, β′ and γ′ as a function of the calculated ΔS data, ΔH data, and SOD data that are linked by the following linear relationship:
• SOD=100%−α′−β′ΔS−γ′ΔH,
• the determined α′, β′ and γ′ parameters associated with a first cell aging corresponding to first aging conditions,
• assessing next values of SOD for the cell when submitted to new discharging conditions, by applying the linear relationship with the determined α′, β′ and γ′ parameters,
• repeating the measuring, the calculating, and the determining for determining changed α′, β′ and γ′ parameters as a function of recalculated ΔS data, ΔH data, and SOC/SOD data that are linked by the linear relationship, and
• the changed α′, β′ and γ′ parameters associated with a second cell aging corresponding to second aging conditions.

A system for assessing a state of charge/discharge (SOC/SOD) for a cell comprising a secondary or rechargeable electrochemical cell, the cell having a first operational mode during which the cell is charged from a power supply connected to terminals of the cell, a second operational mode during which the cell is discharged into a load and a rest mode, the system comprising:

• means for measuring voltage, current and temperature of the cell in a course of the first and second operational modes and during the rest mode,
• means for calculating entropy variation (ΔS) data, enthalpy variation (ΔH) data-, Open-Circuit voltage (OCV) data and state of charge/discharge (SOC/SOD) data, from the voltage, current and temperature measurements,
• means for determining parameters α, β and γ-as a function of the calculated ΔS data, ΔH data, and SOC/SOD data that are linked by the following linear relationship:
• SOC=α+βΔS+γΔH
• SOD=100%−SOC,
• the determined α, β and γ parameters associated with a first cell aging corresponding to a first number of charging cycles of the cell,
• means for assessing next values of SOC/SOD for the cell when submitted to new charging/discharging conditions, by applying the linear relationship with the determined α, β and γ parameters,
• means for repeating the measuring, the calculating, and the determining for determining changed α, β and γ parameters as a function of recalculated ΔS data, ΔH data, and SOC/SOD data that are linked by the linear relationship, and
• the changed α, β and γ parameters associated with a second cell aging corresponding to a second number of charging cycles of the cell.

A system for assessing a state of discharge (SOD) for a cell comprising a primary electrochemical cell, the cell having an operational mode during which the cell is discharged into a load and a rest mode, the system comprising:

• means for measuring voltage, current and temperature of the cell in a course of the operational mode and during the rest mode,
• means for calculating entropy variation (ΔS) data, enthalpy variation (ΔH) data, Open-Circuit voltage (OCV) data and state of discharge (SOD) data, from the voltage, current and temperature measurements,
• means for determining parameters α′, β′ and γ′ as a function of the calculated ΔS data, ΔH data, and SOD data that are linked by the following linear relationship:
• SOD=100%−(α′+β′ΔS+γ′ΔH),
• the determined α′, β′ and γ′ parameters associated with a first cell aging corresponding to first aging condition,
• means for assessing next values of SOD for the cell when submitted to new discharging conditions, by applying the linear relationship with the determined α′, β′ and γ′ parameters, and
• means for repeating the measuring, the calculating, and the determining for determining changed α′, β′ and γ′ parameters as a function of recalculated ΔS data, ΔH data and SOD data that are linked by the linear relationship,
• the changed α′, β′ and γ′ parameters associated with a second cell aging corresponding to second aging conditions.