Coin-Type Lithium Cell Composition for Reflow Soldering Stability
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Solution Overview
Problem
Coin-type lithium secondary cells for soldering by reflow method experience performance deterioration due to reactions between lithium carbonate in the electrodes and the electrolytic solution during high-temperature reflow soldering.
Innovation Solution
The coin-type lithium secondary cell design includes a positive electrode and a negative electrode with a lithium composite oxide, an electrolyte layer containing an electrolytic solution, and a cell case. The electrodes contain 0.002% to 3.0% by mass of lithium carbonate, which is reduced by lowering the lithium content in raw materials and/or rinsing with water to minimize reactions during reflow soldering.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the lithium carbonate content in electrodes is reduced to minimize reactions during reflow soldering, then the performance deterioration is suppressed, but the capacity and energy density may be affected
Solution Approach 1:
The invention optimizes the lithium carbonate content parameter within a specific range (0.002-3.0% by mass) to balance two opposing requirements: maintaining sufficient lithium for high capacity and energy density, while limiting reactions during reflow soldering. This parameter optimization enables the cell to achieve both high performance and good heat resistance.
2Volume of moving object
If the cell is designed to be compact and low-profile with high energy density, then the volume efficiency is improved, but the manufacturing precision and control of lithium carbonate content become more difficult
Solution Approach 1:
The invention controls the lithium carbonate content during the electrode manufacturing process itself, before assembly into the cell. By adjusting the lithium content in raw materials and controlling the sintering conditions, the desired lithium carbonate content (0.002-3.0% by mass) is achieved in advance, ensuring both compact cell design and precise composition control.
Data Source
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AI summary
A coin-type lithium secondary cell (1) for soldering by reflow method includes a positive electrode (2) including a lithium composite oxide, a negative electrode (3), an electrolyte layer (4) provided between the positive electrode (2) and the negative electrode (3) and including an electrolytic solution (42), a cell case (5) having an enclosed space in which the positive electrode (2), the negative electrode (3), and the electrolyte layer (4) are housed. The positive electrode (2) and the negative electrode (3) as a whole contains 3.0% by mass or less of lithium carbonate. Accordingly, it is possible to achieve the coin-type lithium secondary cell (1) with reduced deterioration of performance caused by reflow soldering.