Threshold Discharging C-Rates for Battery Cells in Low Temperature
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Solution Overview
Problem
Battery capacity in electric vehicles (EVs) decreases at low temperatures due to increased internal resistance, limiting their performance in cold environments.
Innovation Solution
A method to determine and apply a threshold discharging C-rate for battery cells in low temperature environments by charging them to a specific state of charge, placing them in a temperature-controlled environment, measuring temperature and discharge capacity, and modifying the C-rate based on these measurements to optimize performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If battery cells operate in low temperature environments, then EVs can function in cold climates, but battery capacity decreases due to increased internal resistance
Solution Approach 1:
The patent changes the operating parameter (C-rate) dynamically based on temperature conditions. By identifying a threshold C-rate specific to each temperature, the system adjusts the discharge rate to optimize battery capacity while maintaining operational capability in cold climates.
Solution Approach 2:
The patent implements a dynamic control strategy where the C-rate is not fixed but adjusted based on real-time temperature measurements. The system transitions from static operation to dynamic adaptation, allowing the battery management system to respond to changing thermal conditions and maintain optimal performance.
2Quantity of substance
If internal resistance is reduced through temperature increase, then battery capacity improves, but additional energy input is required for heating
Solution Approach 1:
The patent utilizes the battery's own discharge process to generate heat through resistive heating (Joule heating). By operating at or above the threshold C-rate, the battery self-heats during normal operation, eliminating the need for external heating systems and converting what would be energy loss into a beneficial effect.
Solution Approach 2:
The patent converts the harmful effect of internal resistance (which causes energy loss and heat generation) into a beneficial effect. The resistive heating that normally reduces efficiency is harnessed to increase battery temperature and improve capacity, turning a disadvantage into an advantage.
3Temperature
If discharging C-rate is increased to generate heat, then internal resistance effects are mitigated, but discharge capacity may be reduced at very high rates
Solution Approach 1:
The patent implements a feedback control mechanism where the actual battery temperature is measured and compared to the threshold temperature. Based on this feedback, the system adjusts the C-rate to maintain optimal operating conditions, preventing both overheating and excessive capacity loss.
Solution Approach 2:
The patent applies partial action by using only the minimum necessary C-rate (threshold C-rate) required to achieve the desired temperature effect. Rather than continuously operating at high C-rates, the system applies just enough discharge current to mitigate internal resistance effects, preserving discharge capacity while achieving temperature benefits.
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 helps mitigate the effects of internal resistance, allowing EVs to maintain or increase battery capacity in cold temperatures by identifying a threshold C-rate where heat generation from discharge becomes dominant over resistance, enhancing their operational efficiency.
Implementation Method 1
heat generation from discharge becomes dominant over resistance
Data Source
AI summary
Techniques described herein relate generally to determining and applying threshold discharging C-rates for battery cells in low temperature environments. To combat internal resistance within a battery cell at low temperature, heat may be generated within a battery cell via a high discharge C-rate. A higher discharge C-rate may cause more heat generation with a battery cell and the higher temperature may mitigate the low temperature environment. As a result of the heat generation, a battery cell's capacity may be increased. Techniques described herein may identify, for a particular low temperature (0 degrees Celsius and below), a threshold discharge C-rate that if a battery cell is discharged above the threshold, the effect of temperature rising would be more dominant than the effect of the internal resistance and more capacity would be obtained from the battery cell.