SVO/CFx Hybrid Cathode Anode Capacity Ratio

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Solution Overview

Problem

Implantable cardioverter defibrillators powered by lithium-silver vanadium oxide cells face issues with impedance growth and unclear end-of-life indicators, leading to reduced effectiveness and potential device failure due to inadequate power source replacement timing.

Innovation Solution

A lithium electrochemical cell design featuring a sandwich cathode configuration with high energy density carbon monofluoride (CFx) and high rate capability silver vanadium oxide (SVO) materials, optimized by adjusting the anode-to-cathode capacity ratio to minimize impedance growth and provide a predictable end-of-life indicator.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Duration of action of moving object

If excess cathode material is used to prevent voltage drop to the second discharge plateau, then cell longevity is improved, but energy density decreases

Engineering Contradiction:

Improvecell longevityVSAvoidenergy density

Core Design Contradiction:

Duration of action of moving objectVSUse of energy by moving object

Solution Approach 1:

The cathode is segmented into two distinct materials: SVO (silver vanadium oxide) and CFx (carbon monofluoride). Each material serves a specific function - SVO provides the first discharge plateau with good rate capability, while CFx provides the second discharge plateau with high energy density. This segmentation allows the cell to achieve both longevity and energy density by utilizing both materials rather than relying on excess of a single material.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Different regions of the cathode have different properties - the SVO component is optimized for rate capability and initial discharge, while the CFx component is optimized for energy density and extended discharge. This local quality differentiation allows each material to perform its specialized function, resolving the contradiction between longevity and energy density.

Inventive Principle:

Principle #3Local quality

2Reliability

If discharge voltage is set on or above the second discharge plateau to avoid rapid loss of pulse capability, then reliability is improved, but useful capacity is substantially lost

Engineering Contradiction:

Improvepulse capabilityVSAvoiduseful capacity

Core Design Contradiction:

ReliabilityVSQuantity of substance

Solution Approach 1:

The cathode is divided into two functional segments: SVO for the first discharge plateau and CFx for the second discharge plateau. This segmentation allows the cell to maintain pulse capability throughout both plateaus, ensuring reliability is improved without substantially losing useful capacity, as each material is optimized for its specific discharge region.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The invention changes the chemical composition parameter of the cathode by introducing CFx material with different electrochemical properties than SVO. This parameter change enables the cell to maintain stable pulse capability across a wider voltage range, from the first plateau (SVO) through the second plateau (CFx), thereby improving reliability without sacrificing useful capacity.

Inventive Principle:

Principle #35Parameter changes

3Productivity

If Li/SVO cell chemistry is used to provide high energy density and high power pulse capability, then productivity is improved, but impedance growth occurs leading to voltage delay

Engineering Contradiction:

Improvehigh power pulse capabilityVSAvoidimpedance growth

Core Design Contradiction:

ProductivityVSReliability

Solution Approach 1:

The cathode uses a composite material system combining SVO and CFx. This composite structure maintains the high power pulse capability of SVO while the CFx component provides stability that reduces impedance growth. The composite materials work together to deliver both high productivity and improved reliability, resolving the contradiction between power capability and impedance stability.

Inventive Principle:

Principle #40Composite materials

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 cell design achieves low impedance growth, reliable end-of-life indication, and high energy density, ensuring effective and timely replacement of the power source, thus enhancing the longevity and reliability of implantable medical devices.

Implementation Method 1

an electrochemical cell whose anode is composed of lithium or some alloy thereof. The cathode is composed of silver vanadium oxide (SVO) and carbon monofluoride (CFx)

Methodology Applied

Scientific EffectElectrochemical reaction: Redox Reactions

Data Source

PatentUS7776470B2Anode-to-cathode capacity ratios for SVO/CF<sub> x </sub>hybrid cathode electrochemical cells

Publication Date: 2010.08.17 GREATBATCH LTD

AI summary

Improvements in the performance of lithium electrochemical cells comprising a first cathode active material of a relatively high energy density but of a relatively low rate capability, for example CFx, contacted to one side of a current collector and with a second cathode active material having a relatively low energy density but of a relatively high rate capability, for example SVO, contacted to the opposite current collector side are described. An exemplary cathode has the configuration: SVO/first current collector/CFx/second current collector/SVO, and wherein the anodic coulombic capacity does not exceed the total coulombic capacities of the SVO and CFx by greater than 25%. Manganese oxide (MnO2) is another typically used cathode active material in lieu of SVO, and the present invention is applicable to lithium cells of that system as well.