Lithium-Ion Cell Capacity Calculation from Charging Knee Points
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Solution Overview
Problem
Existing methods for calculating the state of health (SOH) of lithium-ion cells, such as electric vehicle batteries, are inaccurate due to reliance on estimating state of charge (SOC), leading to errors and potential safety issues from full charging or discharging, which also reduce cell life.
Innovation Solution
A method that calculates cell capacity by detecting knee-point voltages and corresponding electric charges during charging, avoiding full discharge or charge, and using these points to determine cell state without relying on SOC estimation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If full charge or full discharge is used to calculate cell capacity, then the calculation can be completed, but it affects cell life and causes safety problems
Solution Approach 1:
The patent applies partial action by performing charge-discharge cycles only within a specific SOC range (e.g., 10%-90% or 20%-80%) rather than full charge-discharge cycles. This partial cycling approach allows capacity calculation without subjecting the cell to the stress of complete charge-discharge, thereby preserving cell life and safety while still obtaining meaningful capacity data for SOH estimation.
2Measurement precision
If a specific SOC range is selected for charging to calculate capacity, then the calculation can be performed, but it requires large range selection and has high requirements for SOC accuracy
Solution Approach 1:
The patent employs feedback mechanisms through multiple charge-discharge cycles within the restricted SOC range. By repeatedly charging and discharging the cell within the same SOC boundaries and comparing the capacity measurements, the system can verify SOC estimation accuracy and refine the calculation. The feedback from multiple cycles allows the system to identify consistent capacity values while detecting and correcting SOC estimation errors.
Solution Approach 2:
The patent performs preliminary charge-discharge cycles within the restricted SOC range before final capacity calculation. These preliminary cycles serve to stabilize the cell state, verify the SOC estimation accuracy, and establish reliable baseline measurements. By performing these preparatory cycles first, the system ensures that subsequent capacity calculations are based on accurate and stable cell conditions.
3Productivity
If SOC estimation is used to calculate cell state, then the calculation can be performed quickly, but inaccurate SOC estimation leads to large errors in results
Solution Approach 1:
The patent makes the system self-correcting by using the charge-discharge cycles within the restricted SOC range to automatically verify and refine SOC estimation. The capacity measurements obtained from these cycles serve as feedback that allows the system to self-adjust and improve SOC accuracy without external intervention. This self-service approach ensures that even if initial SOC estimation is inaccurate, the system can correct itself through the iterative measurement process.
Data Source
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AI summary
The present disclosure provides a method for calculating a cell state, a computer storage medium, and an apparatus for calculating a cell state, and relates to the technical field of vehicles. The method includes: acquiring a first knee-point voltage threshold of a cell, a first knee-point electricity corresponding to the first knee-point voltage threshold, a second knee-point voltage threshold of the cell and a second knee-point electricity corresponding to the second knee-point voltage threshold; recording a first charging curve of the cell in real time; obtaining a target knee point according to the first charging curve, the first knee-point voltage threshold, and the second knee-point voltage threshold, and obtaining a target-knee-point electricity according to the first knee-point electricity or the second knee-point electricity; detecting the electricity of the cell until the charging is completed, and obtaining a charged electricity of the cell from the target knee point to the completion of charging; and obtaining the capacity of the cell according to the target-knee-point electricity and the charged electricity.