Cyclic Coulometry for Battery Life and Resistance Diagnosis
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Solution Overview
Problem
Current battery evaluation methods, particularly high-precision coulometry, are limited in accurately predicting cycle life due to their inability to concurrently measure coulombic efficiency and internal resistance growth, and they require expensive stable current sources, making them costly and inefficient for characterizing lithium-ion battery performance under various conditions.
Innovation Solution
The implementation of cyclic coulometry, which generates symmetric charge and discharge currents and adjusts charge or discharge times to maintain cell voltage at a setpoint, allowing for concurrent measurement of coulombic efficiency and internal resistance, thereby providing a more comprehensive assessment of battery performance and durability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If high-precision coulometry is used to measure coulombic efficiency, then measurement precision is improved, but device complexity and cost increase due to requiring expensive stable current sources
Solution Approach 1:
The patent transforms the measurement approach by changing from direct coulombic efficiency measurement under fixed conditions to measuring differential capacity loss rates across varying states of charge. This parameter transformation allows using simpler, less stable current sources while still achieving accurate battery performance characterization through the differential measurement technique.
Solution Approach 2:
The patent introduces differential capacity loss rate as an intermediary measurement parameter. Instead of directly measuring coulombic efficiency which requires stable current sources, the method measures capacity loss during charge and discharge cycles as intermediary data, then calculates performance metrics from these differential measurements, bypassing the need for expensive stable current sources.
2Device complexity
If traditional coulometry measures only coulombic efficiency, then measurement simplicity is maintained, but measurement completeness deteriorates by failing to concurrently measure internal resistance growth
Solution Approach 1:
The patent makes the measurement system multi-functional by enabling simultaneous measurement of multiple battery parameters (capacity loss rates, internal resistance growth, coulombic efficiency) using the same differential measurement apparatus. This universal measurement approach eliminates the need for separate specialized equipment for each parameter while maintaining measurement simplicity.
Solution Approach 2:
The patent merges multiple measurement functions into a single integrated measurement process. By combining capacity loss measurement during charge and discharge into one differential measurement sequence, the system simultaneously extracts multiple performance parameters including internal resistance growth, eliminating the need for separate measurement systems for each parameter.
3Ease of operation
If fixed current cycling is used for battery testing, then ease of operation is maintained, but productivity decreases due to inability to accelerate testing
Solution Approach 1:
The patent introduces dynamic measurement capabilities by varying the state of charge ranges and cycling conditions during testing. Instead of fixed current cycling at constant conditions, the method dynamically adjusts measurement parameters and analyzes differential capacity loss across varying states, enabling accelerated testing while maintaining operational simplicity through automated differential measurements.
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
Cyclic coulometry enhances battery testing by accurately measuring capacity loss, internal resistance growth, and differential loss rates under different conditions, offering a more precise and cost-effective characterization of battery performance and cycle life, enabling faster iteration in battery design and development.
Implementation Method 1
Coulometry is an electrochemical technique that measures the total coulombs of electricity consumed or produced during electrochemical reactions
Implementation Method 2
In both cases, the total charge, Q, passed through the electrochemical cells is calculated by integrating the current as a function of time
Data Source
Figure 1
Figure 2A~2C
Figure 3A~3B
AI summary
Systems, devices, and methods of diagnosing an electrochemical cell using cyclic coulometry are discussed. An exemplary battery diagnostic system comprises a current generator to generate symmetric charge current and discharge current to excite an electrochemical cell, and a cyclic coulometer to evaluate performance of the electrochemical cell. The cyclic coulometer can adjust at least one of a charge time for applying the charge current, or a discharge time for applying the discharge current, to keep a monitored cell voltage toward a specific setpoint. The adjustment of charge or discharge time can be achieved by changing a current switch timing for reversing current from a first to a second current direction. The cyclic coulometer measures one or more electrical parameters during the charge or discharge cycle, and generates a performance metric using the measured electrical parameters.