Sandwich Cathode Lithium Battery for Implantable Devices
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Solution Overview
Problem
Existing electrochemical cells for implantable medical devices face challenges in balancing high discharge capacity and high rate capability, with materials like carbon monofluoride (CFx) offering high capacity but low rate capability, and silver vanadium oxide (SVO) providing high rate capability but low capacity, necessitating a design that combines both effectively.
Innovation Solution
A sandwich cathode design featuring a first cathode active material with high energy density but low rate capability (CFx) sandwiched between two current collectors, paired with a second active material of low energy density but high rate capability (SVO), optimized for increased energy density and improved rate capability, along with an efficient manufacturing process that reduces manual steps and manufacturing time.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If carbon monofluoride (CFx) cathode material is used to increase discharge capacity, then delivery capacity is improved, but rate capability deteriorates
Solution Approach 1:
The cathode is divided into two separate active materials (CFx and SVO) that are physically separated into distinct layers, each performing its specialized function. The CFx layer provides high capacity while the SVO layer provides high rate capability, resolving the contradiction by segmentation rather than mixing the materials.
Solution Approach 2:
Different regions of the cathode are assigned different material properties: the CFx layer is optimized for high discharge capacity while the SVO layer is optimized for high rate capability. This local differentiation allows each material to excel at its designated function without compromising the other.
2Speed
If silver vanadium oxide (SVO) cathode material is used to increase rate capability, then rate capability is improved, but delivery capacity deteriorates
Solution Approach 1:
The cathode is divided into two separate active materials (CFx and SVO) that are physically separated into distinct layers, each performing its specialized function. The SVO layer provides high rate capability while the CFx layer provides high capacity, resolving the contradiction by segmentation rather than mixing the materials.
Solution Approach 2:
Different regions of the cathode are assigned different material properties: the SVO layer is optimized for high rate capability while the CFx layer is optimized for high discharge capacity. This local differentiation allows each material to excel at its designated function without compromising the other.
3Device complexity
If a single cathode material is used to simplify design, then device complexity is reduced, but energy density deteriorates
Solution Approach 1:
The cathode uses a composite structure with two distinct active materials (CFx and SVO) in separate layers, combining the high capacity advantage of CFx with the high rate capability advantage of SVO. This composite approach achieves superior overall performance compared to either material alone, justifying the increased design complexity.
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
The design enhances energy density and rate capability, providing increased discharge capacity at high rates, as demonstrated by improved pulse discharge performance compared to prior art cells, with test cells showing a 34.6% increase in discharge capacity at specific voltages and 15.4% increase in energy density per volume.
Implementation Method 1
Electrochemical cells provide electrical energy that powers a host of electronic devices... conversion of chemical energy to electrical energy
Data Source
AI summary
A lithium electrochemical cell with increased energy density is described. The electrochemical cell comprises an improved sandwich cathode design with a second cathode active material of a relatively high energy density but of a relatively low rate capability sandwiched between two current collectors and with a first cathode active material having a relatively low energy density but of a relatively high rate capability in contact with the opposite sides of the two current collectors. In addition, a cathode fabrication process is described that increases manufacturing efficiency. The cathode fabrication process comprises a process in which first and second cathode active materials are directly applied to opposite surfaces of a perforated current collector and laminated together. The present cathode design is useful for powering an implantable medical device requiring a high rate discharge application.