Battery Deterioration Estimation via Transient Impedance Measurement
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Solution Overview
Problem
Existing methods fail to accurately estimate the degree of deterioration of secondary batteries with metallic lithium layers due to steady dissolution and precipitation of metallic lithium during discharge, which complicates the measurement of SEI film resistance and internal impedance.
Innovation Solution
A battery deterioration estimation apparatus that measures discharge current and voltage drop directly after discharge starts, calculates the internal impedance of the secondary battery, and uses this information to accurately estimate the degree of growth of the SEI film and subsequently the battery's deterioration level.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If internal impedance is measured during steady discharge, then discharge performance can be evaluated, but diffusion resistance contaminates the measurement making SEI film resistance inaccurate
Solution Approach 1:
The patent applies preliminary action by measuring the internal impedance immediately after discharge starts, before the steady-state dissolution and precipitation of metallic lithium becomes established. This timing captures the impedance primarily reflecting SEI film resistance before diffusion resistance significantly contributes to the measurement.
Solution Approach 2:
The patent applies skipping by rapidly capturing the impedance measurement in the transient period right after discharge initiation, effectively skipping through the period before diffusion resistance becomes dominant. This allows obtaining accurate SEI film resistance data without waiting for steady-state conditions.
2Power
If discharge current flows to evaluate battery performance, then power output can be assessed, but metallic lithium dissolution and precipitation becomes steady causing diffusion resistance to dominate
Solution Approach 1:
The patent performs the impedance measurement as a preliminary action immediately when discharge starts, capturing the electrical characteristics before the metallic lithium dissolution and precipitation reaches steady state. This ensures the measured impedance reflects SEI film properties rather than diffusion resistance.
3Reliability
If SEI film growth is estimated from internal impedance during steady discharge, then battery deterioration can be monitored, but diffusion resistance accounts for larger proportion of internal impedance
Solution Approach 1:
The patent applies preliminary action by performing the impedance measurement immediately after discharge starts, before steady-state conditions establish. This timing allows accurate estimation of SEI film growth and battery deterioration by capturing impedance data before diffusion resistance becomes the dominant factor.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Enables accurate estimation of secondary battery deterioration by measuring internal impedance shortly after discharge begins, avoiding the effects of steady-state diffusion resistance and allowing for precise assessment of SEI film growth and battery health.
Implementation Method 1
a current measurer configured to measure a discharge current of the secondary battery
Implementation Method 2
a voltage measurer configured to measure a voltage drop that is a difference between a voltage of the secondary battery before the start of discharging and a voltage of the secondary battery at the prescribed timing
Implementation Method 3
a calculator configured to calculate an internal impedance of the secondary battery at the prescribed timing from the measured discharge current and the measured voltage drop
Data Source
AI summary
A battery deterioration estimation apparatus is equipped with a current measurement unit, a voltage measurement unit, a calculation unit, and an estimation unit. The current measurement unit measures a discharge current of the secondary battery at a prescribed timing that is directly after the start of discharge by the secondary battery. The voltage measurement unit measures a voltage drop that is the difference between the voltage of the secondary battery before the start of discharge and the voltage of the secondary battery at the prescribed timing described above. The calculation unit calculates the internal impedance of the secondary battery at the above-described prescribed timing from the measured discharge current and the measured voltage drop. The estimation unit estimates the degree of deterioration of the secondary battery from the calculated internal impedance.