Li/SVO Cathode Surface Area Control for Voltage Delay
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Solution Overview
Problem
Lithium/silver vanadium oxide (Li/SVO) cells experience voltage delay and irreversible resistance growth during pulse discharging, particularly at 25% to 70% depth-of-discharge, which limits their effectiveness in powering implantable medical devices and requires complex discharge regimes for reforming.
Innovation Solution
An electrochemical cell with a cathode made from a low surface area active material, such as silver vanadium oxide, copper silver vanadium oxide, or other materials with a surface area between 0.2 m2/gram and 2.6 m2/gram, in the form of a free-standing sheet contacted to a current collector, to minimize irreversible resistance growth and voltage delay.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If high surface area cathode active material is used, then discharge capacity is improved, but voltage delay and irreversible Rdc growth increase
Solution Approach 1:
The patent applies parameter changes by controlling the surface area of the cathode active material to a specific range (0.2-2.6 m2/gram). This parameter optimization resolves the contradiction by finding the optimal surface area value that provides sufficient discharge capacity while minimizing voltage delay and irreversible Rdc growth during pulse discharge operations.
2Reliability
If complex discharge regimes are applied for reforming, then voltage delay and Rdc growth are reduced, but energy consumption increases
Solution Approach 1:
The patent applies preliminary action by pre-controlling the surface area of the cathode active material during manufacturing (0.2-2.6 m2/gram). This preliminary structural control prevents voltage delay and irreversible Rdc growth from occurring in the first place, eliminating the need for subsequent energy-consuming reforming discharge regimes.
3Reliability
If low surface area cathode active material is used, then voltage delay and irreversible Rdc growth are reduced, but discharge capacity decreases
Solution Approach 1:
The patent resolves this contradiction by precisely controlling the surface area parameter within the optimal range of 0.2-2.6 m2/gram. This parameter optimization ensures that the cathode active material maintains sufficient discharge capacity while simultaneously minimizing voltage delay and irreversible Rdc growth, achieving both reliability and capacity 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
The use of low surface area cathode materials reduces irreversible resistance growth and voltage delay, allowing the Li/SVO cell to maintain high discharge capacity and extend its useful life without the need for energy-consuming reforming methodologies, ensuring reliable performance in medical devices.
Implementation Method 1
conversion of chemical energy to electrical energy
Implementation Method 2
vanadium compounds become soluble in the cell electrolyte from the cathode
Data Source
AI summary
An electrochemical cell comprising a lithium anode, a cathode comprising a blank cut from a free-standing sheet of a silver vanadium oxide mixture contacted to a current collector. The active material has having a relatively lower surface area and an electrolyte activating the anode and the cathode is described. By optimizing the cathode active material surface area in a SVO-containing cell, the magnitude of the passivating film growth at the solid-electrolyte interphase (SEI) and its relative impermeability to lithium ion diffusion is reduced. Therefore, by using a cathode of an active material in a range of from about 0.2 m2/gram to about 2.6 m2/gram, and preferably from about 1.6 m2/gram to about 2.4 m2/gram, it is possible to eliminate or significantly reduce undesirable irreversible Rdc growth and voltage delay in the cell and to extend its useful life in an implantable medical device.