3D Battery Constraint Adhesive for Electrode Expansion Control
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Solution Overview
Problem
The persistent challenge in rocking chair battery cells is the expansion and contraction of electrodes during repeated charging and discharging, which leads to electrical shorts and battery failures, reducing the reliability and cycle life of the battery.
Innovation Solution
The implementation of a constraint adhesive system that securely holds constraint structures in position within the battery, using an electrically-insulating, thermoplastic, hot-melt adhesive to adhere the electrode assembly to a constraint system, thereby controlling the expansion and contraction of electrodes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Duration of action of moving object
If electrodes are allowed to expand and contract during battery cycling, then the battery can operate through charge/discharge cycles, but electrical shorts and battery failures occur due to uncontrolled expansion
Solution Approach 1:
The constraint system is installed in advance within the battery assembly to preemptively counteract the expansion forces of electrodes during cycling. The constraints apply continuous compressive force on the electrode assembly, preventing expansion before it can cause electrical shorts or structural failure, thereby simultaneously enabling long-term cycling and maintaining reliability
2Reliability
If constraint structures are added to control electrode expansion, then electrode growth is restrained and reliability improves, but the device complexity increases
Solution Approach 1:
The constraint system utilizes flexible constraint members and adhesive layers that conform to the electrode assembly shape. These thin, flexible components apply distributed compressive forces without requiring complex rigid mechanical structures, thereby improving reliability while minimizing increases in device complexity
Solution Approach 2:
The constraint system is integrated directly into the battery assembly structure, with constraint members positioned between existing battery components and the adhesive bonding the constraint system to the electrode assembly. This merging approach incorporates the constraint function into the existing battery architecture rather than adding separate external systems, reducing overall complexity
3Reliability
If adhesive is used to secure constraint structures, then the constraints are held in position to control expansion, but adhesion is lost under long-term exposure to electrolyte conditions
Solution Approach 1:
The adhesive composition is formulated with specific chemical parameters optimized for resistance to electrolyte exposure, including cross-linking density, hydrophobicity, and chemical inertness. These parameter changes enable the adhesive to maintain strong bonding between the constraint system and electrode assembly throughout the battery's operational lifetime, preventing constraint failure while ensuring long-term durability in the harsh electrolyte environment
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 solution improves the energy density, reliability, and cycle life of batteries by effectively restraining electrode growth and preventing electrical shorts and failures.
Implementation Method 1
an electrically-insulating, thermoplastic, hot-melt adhesive having (i) a melting temperature in the range of 75° C. to 130° C.
Data Source
AI summary
An electrode assembly for a secondary battery and method are provided. The electrode assembly comprises a population of unit cells and a constraint system. The electrode assembly comprises a population of electrode structures, a population of counter-electrode structures, and an electrically insulating separator material. The constraint system comprises (i) first and second primary growth constraints separated in the longitudinal direction, (ii) first and second connecting members separated in the vertical direction that connect the first and second primary growth constraints and a subset of the members of the electrode or counter-electrode population. The first and second connecting members are adhered to the subset by an electrically-insulating, thermoplastic, hot-melt adhesive having (i) a melting temperature in the range of 75° C. to 130° C., and (ii) a melt index value as measured according to ASTM D1238 in a range of at least 20 to no more than 350.