Lithium Primary Cell with pH-Modified Electrolyte for Void Volume Management
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Solution Overview
Problem
Existing primary electrochemical cells face challenges in balancing improved discharge performance with the need for increased void volume to accommodate reaction products, while also ensuring reliability against physical abuse and partial discharge.
Innovation Solution
The use of an iron disulfide cathode material and a non-aqueous electrolyte comprising specific solvents, salts, and pH-modifiers, along with a Positive Temperature Coefficient (PTC) device and optimized cell dimensions, including a gasket material and separator, enhances discharge performance and physical abuse resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the cathode material composition is refined to increase discharge performance, then discharge performance is improved, but the volume of reaction products increases requiring more void volume
Solution Approach 1:
The patent modifies the chemical composition parameters of the electrolyte by incorporating specific pH-modifiers (ammonium carbonate, ammonium bicarbonate, or lithium carbonate) to control the chemical environment during discharge. This allows the cell to achieve improved discharge performance while managing the volume expansion of reaction products through controlled chemical reactions that produce smaller volume byproducts or facilitate better packing of discharge products.
2Productivity
If internal cell volume is maximized for active material by reducing housing, seal, and separator thickness, then discharge performance is improved, but physical abuse resistance deteriorates
Solution Approach 1:
The patent employs composite material strategies by combining multiple electrolyte components (solvents, salts, and pH-modifiers) to create an electrolyte system that provides both high ionic conductivity for performance and adequate buffering capacity for physical stress. The specific combination of dioxolane, sulfolane, and 3,5-dimethylisoxazole creates a composite electrolyte system that maintains cell integrity under physical abuse while enabling high discharge performance.
3Use of energy by moving object
If discharge depth is increased to improve performance, then more energy is delivered, but volume of reaction products increases requiring more void volume
Solution Approach 1:
The patent converts the potentially harmful volume expansion from deep discharge into a beneficial effect by using pH-modifiers that control the formation of reaction products. The ammonium carbonate, ammonium bicarbonate, or lithium carbonate additives manage the chemical reactions during deep discharge to produce reaction products with smaller volume or better packing characteristics, thereby enabling high energy delivery without proportionally increasing void volume requirements.
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 configuration improves discharge performance, stability, and physical abuse resistance, maintaining performance even after high-temperature storage and passing conventional physical abuse tests by ensuring adequate void volume and minimizing the risk of failure.
Implementation Method 1
the composition of the electrolyte is modified by the inclusion of a pH-modifier, which is an inorganic additive selected from the group consisting of ammonium carbonate, ammonium bicarbonate, and combinations thereof
Implementation Method 2
a non-aqueous electrolyte in fluid communication with the anode, cathode and separator, wherein said electrolyte comprises a solvent, a salt dissolved therein
Implementation Method 3
the electrochemical processes or reactions that occur within the cell result in an increase of cathode thickness upon discharge, and an accompanying formation of reaction products
Data Source
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AI summary
The present disclosure is directed to a primary electrochemical cell having an improved discharge performance, and/or improved reliability under physical abuse and/or partial discharge. More particularly, the present disclosure is directed to such a primary cell that comprises an improved cathode material (8) comprising a mixture of iron disulfide and a selected pH-modifier and an improved non-aqueous electrolyte that comprises a solvent, a salt, pH-modifiers, and selected organic or inorganic additives, which improve cell stability and discharge performance.