Wound Electrode Assembly Pressing for Stable Electrolyte Permeation
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Solution Overview
Problem
Hollow active material particles in energy storage devices are prone to deformation during charge-discharge cycles, leading to increased resistance and electrolyte solution depletion, which accelerates device deterioration.
Innovation Solution
The energy storage device is designed with a wound-type electrode assembly where the winding axis is parallel to the horizontal direction, and a central part is pressed, with excess electrolyte solution present between the assembly and the case, ensuring the width of the active material layers and separator satisfy specific ratios relative to the electrolyte solution height, facilitating uniform electrolyte permeation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If hollow active material particles are used to increase power, then the area of contact between active material particles and electrolyte solution is increased, but the particles are likely to be deformed with repeated charge-discharge, leading to decreased conductivity and increased resistance
Solution Approach 1:
The electrode assembly is pressed in advance during manufacturing to pre-compress the hollow active material particles. This preliminary compression prevents excessive expansion during charge-discharge cycles, maintaining particle integrity and preventing deformation that would lead to increased resistance and reduced reliability.
2Reliability
If the electrode assembly is pressed to suppress expansion of hollow active material particles, then particle deformation is reduced, but electrolyte solution is pushed out and may take several minutes to several hours to permeate completely into the electrode assembly, causing electrolyte depletion in certain regions
Solution Approach 1:
The pressing force is applied selectively to specific regions of the electrode assembly, and the electrolyte solution is supplied in greater amounts to centrally-pressed regions. This local compensation ensures that pressed areas, which have reduced porosity and slower permeation rates, receive adequate electrolyte supply to prevent depletion and maintain reliable operation.
Solution Approach 2:
The electrode assembly is pressed with a degree of compression that is sufficient to stabilize particles but may initially reduce electrolyte distribution. Excess electrolyte is then supplied to compensate for this reduction, ensuring complete permeation and preventing electrolyte depletion in pressed regions during operation.
3Reliability
If the central part of the electrode assembly is pressed, then hollow active material particle expansion is suppressed, but the electrolyte solution is more likely to be depleted at the central part, increasing resistance and accelerating deterioration
Solution Approach 1:
The pressing operation is applied specifically to the central part of the electrode assembly to stabilize particles in this region. Concurrently, the electrolyte solution supply is increased to the central region to compensate for the reduced permeation rate caused by pressing, preventing electrolyte depletion and maintaining adequate electrolyte quantity for reliable operation.
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 design maintains low resistance after charge-discharge cycles by ensuring uniform electrolyte distribution, preventing electrolyte depletion and reducing resistance.
Implementation Method 1
the electrolyte solution in the hollows is pushed out to flow out of the electrode assembly. Then, at the time of discharge, as the hollow active material particles return to the original shapes, the electrolyte solution will flow into the hollows of the particles. Such inflow of the electrolyte solution into the electrode assembly is caused by capillary action
Data Source
AI summary
An aspect of the present invention is an energy storage device including: an electrode assembly obtained by winding a band-shaped positive electrode including a positive active material layer, a band-shaped negative electrode including a negative active material layer, and a band-shaped separator in the longitudinal direction; an electrolyte solution; and a case that houses the electrode assembly and the electrolyte solution, where at least one of the positive active material layer and the negative active material layer contains a hollow active material particle, the winding axis of the electrode assembly is located parallel to the horizontal direction, at least a central part of the electrode assembly is pressed with the case pressed, an excess electrolyte solution that is a part of the electrolyte solution is present between the electrode assembly and the case, the lower end of the electrode assembly has contact with the excess electrolyte solution, and the relationship between the height H from the liquid level of the excess electrolyte solution to the upper end of the electrode assembly and the width Wc of the positive active material layer satisfies the following formula 1:0.8H≤Wc≤2.0H 1