Assembled Battery Cell Stack Voltage Equalization
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Solution Overview
Problem
Conventional assembled battery manufacturing processes result in variations in voltage between cells due to differences in internal resistance, discharging equipment, environmental conditions, and time, leading to performance deterioration and safety concerns during storage and delivery.
Innovation Solution
A method involving a first adjustment of cell charging rates, assembly into an unconnected cell stack, and a second adjustment through collective discharging to equalize charging rates, eliminating the need for a power source and ensuring safety by setting the final charging rate to a lower limit within the applicable range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If cells are discharged individually before assembly to adjust SOC, then each cell can be inspected and adjusted to minimum applicable percentage, but voltage variations between cells increase due to individual differences in internal resistance, discharging equipment, environmental conditions, and time
Solution Approach 1:
The patent merges multiple individual cell discharging operations into a single collective discharging operation performed on all cells simultaneously after assembly. This is achieved by connecting all cells in parallel through a common discharging circuit, allowing uniform discharging conditions to be applied to all cells, thereby eliminating voltage variations caused by individual discharging differences.
Solution Approach 2:
The patent performs the collective discharging operation after cell assembly but before final inspection and delivery. This preliminary action ensures that voltage variations are corrected at an optimal point in the manufacturing process, allowing subsequent inspections to be performed on cells with minimized voltage differences.
2Manufacturing precision
If cells are charged to high SOC after assembly to equalize voltages, then voltage variations between cells are reduced, but a power source is required and safety concerns arise during storage and delivery
Solution Approach 1:
Instead of charging cells to equalize voltages (which creates safety issues), the patent inverts the approach by discharging cells to equalize voltages. This is achieved by connecting all cells in parallel and allowing them to discharge collectively to a target SOC, which naturally equalizes voltages while avoiding the safety concerns associated with high SOC states.
Solution Approach 2:
The collective discharging system allows cells to equalize their voltages through their own natural discharge characteristics when connected in parallel. The system uses the cells' inherent properties (internal resistance, capacity) to automatically balance their states without requiring complex external control mechanisms or additional power sources.
3Reliability
If multiple inspection steps are performed at different stages, then cell quality is thoroughly verified, but manufacturing time and process complexity increase
Solution Approach 1:
The patent performs the collective discharging operation as a preliminary step before final inspection, ensuring that voltage equalization is completed beforehand. This allows the final inspection to focus solely on verifying the equalized state without needing to perform additional equalization steps, thereby streamlining the manufacturing process.
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 method effectively reduces voltage variations between cells, ensuring consistent performance and safety by equalizing voltages during the manufacturing process, thereby avoiding the need for post-assembly charging and enhancing storage and delivery safety.
Implementation Method 1
a second adjustment step for collectively discharging at least two constituent cells of the cell stack such that their charging rates become equal to a second charging rate that is lower than the first charging rate
Data Source
AI summary
Cells (1) are first manufactured (S01). Each cell (1) is inspected (S02) and then adjusted to SOC 40% (S03). Thereafter, the cells (1) are assembled to form a cell stack (90) (S04). In the cell stack (90), the cells (1) constituting the cell stack (90) are collectively discharged so that their SOC becomes 30% (S05). This collective discharge is performed to collectively discharge the cells (1) in the cell stack (90). Thus, the same discharging conditions (equipment, time, environment, etc.) are established for the cells (1).