Lithium Ion Battery Cell Capacity Balancing via Preliminary Discharge
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Solution Overview
Problem
Lithium ion battery packs with cells of varying charge storage capacities lead to voltage imbalances during charging and discharging, potentially damaging cells when one cell is depleted while others still have capacity, requiring complex and costly protection systems to prevent.
Innovation Solution
A method involving discharging each cell to a predetermined low capacity, stopping discharge when a threshold voltage is reached, and then charging all cells equally until one reaches a maximum voltage, thereby balancing capacities and preventing cell damage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If cells are charged to a predetermined voltage without capacity balancing, then charging speed is improved, but voltage imbalances occur causing cell damage and requiring complex protection systems
Solution Approach 1:
The system performs preliminary discharge of all cells to a predetermined low capacity level before charging. This preliminary action ensures that all cells start from the same capacity baseline, preventing voltage imbalances during subsequent charging operations and eliminating the need for complex protection systems.
Solution Approach 2:
The system changes the operating parameters by discharging cells to a specific low capacity threshold before charging. This parameter change (setting a predetermined low capacity level) standardizes the starting point for all cells, ensuring they charge at the same rate and maintain voltage balance throughout the charging cycle.
2Reliability
If protection systems are added to prevent cell damage, then cell reliability is improved, but device complexity and cost increase
Solution Approach 1:
The system uses the cells themselves to monitor and regulate their own charging process. By discharging all cells to a predetermined low capacity level before charging, the system enables the cells to self-regulate their charging rates, eliminating the need for external protection circuits and reducing overall system complexity.
3Loss of time
If cells with varying capacities are charged equally, then charging time is reduced, but cells with lower capacity are overcharged causing damage
Solution Approach 1:
The system performs a preliminary discharge step where all cells are discharged to a predetermined low capacity level before charging begins. This preliminary action equalizes the starting capacity of all cells, allowing them to be charged equally without risk of overcharging cells with originally lower capacity.
Solution Approach 2:
The system changes the charging parameter by first discharging cells to a specific low capacity threshold. This parameter change creates a standardized starting point that allows all cells to be charged at the same rate and to the same voltage level without causing overcharge damage to any individual cell.
Data Source
AI summary
A method comprises discharging each of a plurality of cells of a battery pack, stopping the discharging of a selected cell of the plurality of cells when the selected cell reaches a predetermined capacity, and charging the plurality of cells after the discharging has stopped for all of the plurality of cells.