Hermetic Ceramic Cell Seal via Laser Welded Metallization
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Solution Overview
Problem
Conventional sealing techniques fail to consistently prevent moisture ingress and egress in miniature electrochemical cells with volumes less than 0.5 cc, leading to reduced longevity and contamination issues, especially for lithium cells, and existing encapsulation methods do not accommodate dimensional changes during charging and discharging.
Innovation Solution
The use of ceramic casings with hermetically sealed ring-shaped metallizations and a gap for expansion, along with a solid electrolyte, to create a flexible and reliable hermetic enclosure for miniature electrochemical cells, allowing for the integration of lithium-ion cells with carbon-based anodes and metal-oxide cathodes, and employing gold or titanium metallization for terminal contact.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional sealing techniques are used in miniature electrochemical cells, then the cell can be sealed, but the seal cannot consistently prevent moisture ingress and egress, leading to reduced longevity
Solution Approach 1:
The patent uses a composite sealing structure combining a rigid ceramic casing with a flexible polymer adhesive layer. The ceramic provides structural integrity and chemical stability, while the polymer layer provides flexibility to accommodate dimensional changes during charging/discharging cycles. This composite approach resolves the contradiction by maintaining consistent sealing performance over extended periods.
Solution Approach 2:
The patent modifies the sealing approach by transitioning from traditional metal seals to a ceramic-polymer composite seal. The polymer adhesive layer changes the sealing mechanism from rigid mechanical sealing to a combination of chemical adhesion and flexible accommodation, allowing the seal to maintain integrity despite cell expansion and contraction during operation.
2Volume of moving object
If the cell size is reduced to below 0.5 cc, then miniaturization is achieved, but the seal takes up a major portion of the overall cell volume
Solution Approach 1:
The patent employs a thin film polymer adhesive layer as the sealing mechanism. This thin film approach minimizes the volume occupied by the seal while providing adequate sealing performance. The flexible nature of the thin polymer layer allows it to accommodate cell dimensional changes without requiring bulky sealing structures, thus resolving the volume contradiction in miniaturized cells.
3Ease of manufacture
If polymeric adhesive layer is used to attach lid to substrate, then assembly is simplified, but the seal cannot consistently prevent ingress of atmospheric contaminants
Solution Approach 1:
The patent creates a composite sealing system where the polymer adhesive layer works in conjunction with the ceramic substrates. The ceramic provides a rigid, chemically stable foundation that resists contaminant penetration, while the polymer layer provides flexible adhesion and sealing. This composite structure maintains both ease of manufacture and reliable contaminant prevention.
Solution Approach 2:
The polymer adhesive layer acts as an intermediary between the rigid ceramic lid and substrate. It mediates the mechanical stress and dimensional changes, providing a flexible bonding interface that maintains sealing integrity. The polymer's adhesive properties ensure consistent attachment while accommodating the thermal and mechanical expansion/contraction cycles.
4Duration of action of moving object
If hermetic encapsulation is applied to accommodate dimensional changes during cycling, then cell functionality is maintained, but the encapsulation structure becomes more complex
Solution Approach 1:
The patent uses the flexible polymer adhesive layer as the encapsulation mechanism that accommodates dimensional changes during charging and discharging cycles. This thin flexible film provides the necessary compliance without requiring complex mechanical expansion joints or adjustable structures, thus maintaining relatively simple device architecture while ensuring cycling durability.
Data Source
AI summary
A miniature electrochemical cell having a total volume that is less than 0.5 cc is described. The cell casing is formed by joining two ceramic casing halves together. One or both casing halves are machined from ceramic to provide a recess that is sized and shaped to contain the electrode assembly. The opposite polarity terminals are metal feedthroughs, such as of gold, and are formed by brazing gold into openings machined into one or both of ceramic casing halves. A thin film metallization, such as of titanium, contacts an edge periphery of each ceramic casing half. The first ceramic casing half is moved into registry with the second ceramic casing half so that the first and second ring-shaped metallizations contact each other. Then, a laser welds through one of the casing halves being a substantially transparent ceramic, for example sapphire, to braze the first and second ring-shaped metallizations to each other to thereby join the first and second casing halves together to form a casing housing the electrode assembly. A solid electrolyte (LixPOyNz) activates the electrode assembly.