Fast Charging Method Using Impedance Measurements
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Solution Overview
Problem
Rapid charging of lithium-ion batteries for electric vehicles poses challenges due to high self-heating, metallic lithium deposition, and accelerated aging, which are exacerbated by varying state of health and temperature discrepancies, leading to conservative charging strategies that prolong charging times and risk cell damage.
Innovation Solution
A method utilizing impedance measurements to determine cell temperature, state of charge, and state of health, allowing for optimized charging profiles that adjust current and voltage to minimize aging and prevent damage, by continuously monitoring voltage and impedance across multiple frequencies and adjusting charging conditions accordingly.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If high charging currents are used for rapid charging, then charging time is reduced, but self-heating increases and cell temperature rises
Solution Approach 1:
The charging current is dynamically adjusted based on real-time impedance measurements and temperature monitoring. The method transitions from static charging profiles to dynamic control where charging parameters continuously adapt to cell conditions, enabling higher currents when safe and reducing them when temperature rises
Solution Approach 2:
The system implements feedback control by continuously measuring impedance and temperature, then using this information to adjust charging current. The impedance measurements provide real-time feedback on cell state, allowing the control system to optimize charging current while preventing excessive temperature rise
2Productivity
If high charging currents are applied, then charging speed increases, but metallic lithium deposition occurs at the anode
Solution Approach 1:
The system performs preliminary impedance measurements to assess cell conditions before applying high charging currents. By evaluating cell readiness in advance through impedance characterization, the method prevents lithium deposition by ensuring charging conditions are appropriate before initiating high-current charging phases
Solution Approach 2:
The method changes charging parameters based on impedance measurements. By monitoring impedance changes that indicate approaching lithium deposition thresholds, the system adjusts charging current parameters to remain within safe operating limits while maximizing charging speed
3Productivity
If charging strategies are optimized for new cells, then charging efficiency is improved, but cells with poor state of health experience problems
Solution Approach 1:
The charging strategy is customized to each cell's specific state of health and condition. Instead of applying a uniform charging profile to all cells, the method determines individual impedance characteristics and adjusts charging parameters locally for each cell based on its unique properties and aging state
Solution Approach 2:
The system dynamically adapts charging strategies based on real-time impedance measurements that reflect current cell health. This allows the charging profile to evolve with cell aging, maintaining optimal charging efficiency for new cells while automatically adjusting to safer parameters for aged cells with poor state of health
4Device complexity
If cell voltage is used to determine state of charge, then measurement is simplified, but accuracy decreases due to temperature and state of health dependencies
Solution Approach 1:
The system uses impedance measurements as an intermediary parameter to accurately determine state of charge. Instead of relying directly on voltage alone, the method introduces impedance as a mediating measurement that, when combined with voltage data, provides temperature and state-of-health-compensated SOC calculation
Solution Approach 2:
The state of charge determination uses a composite approach combining multiple measurement types (voltage and impedance). This composite measurement strategy leverages the complementary information from different measurement modalities to achieve accurate SOC determination that accounts for temperature and aging effects
5Reliability
If conservative charging strategies are used to prevent cell damage, then cell safety is improved, but charging time increases significantly
Solution Approach 1:
The system dynamically optimizes the balance between safety and charging speed by continuously monitoring impedance and temperature. Rather than using fixed conservative limits, the method adjusts charging current in real-time based on actual cell conditions, enabling faster charging when conditions permit while maintaining safety margins
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
This approach enables faster charging while preventing premature aging and damage by dynamically adjusting charging conditions based on real-time impedance data, ensuring safer and more efficient battery charging.
Implementation Method 1
optimized rapid-charging conditions are ascertained depending on at least one of the cell temperature T, SOC and SOH using impedance measurements or impedance spectroscopy (EIS)
Implementation Method 2
High charging currents, for example in the range of 2C or more, are required for this. However, such charging currents can lead to intense self-heating
Data Source
AI summary
A method for fast charging from an initial charge state SOC0 to a predefined target charge state SOCtarget is provided. Optimized fast charging conditions are determined using impedance measurements or impedance spectroscopy (EIS) of a battery system which includes a plurality of lithium ion cells. Units consisting of individual cells or of blocks of cells connected in parallel are connected in series, and devices for measuring the voltage and at least one component of the impedance of these cell units are also provided.