Lithium Cell Electrolyte Additives for Voltage Delay Reduction
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Solution Overview
Problem
Conventional nonaqueous organic electrolytes used in lithium electrochemical cells, such as those powering implantable medical devices, face challenges in achieving high conductivity and stability, leading to voltage delays due to vanadium ion dissolution and impedance build-up, which affects the performance and discharge capacity of lithium-SVO and lithium-SVO/CFx mixture cells.
Innovation Solution
A new electrolyte system is developed using lithium hexafluoroarsenate dissolved in a solvent mixture of propylene carbonate and dimethoxyethane, with dibenzyl carbonate, lithium bis(oxalato)borate, and fluoroethylene carbonate added to enhance conductivity and stability, specifically in ratios that balance conductivity and stability, reducing voltage delays and improving energy and power density.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional nonaqueous organic electrolytes (e.g., LiAsF6 in PC:DME) are used to achieve high conductivity, then conductivity is improved, but voltage delays occur due to vanadium ion dissolution and impedance build-up
Solution Approach 1:
The patent introduces CFx (fluorinated carbon) as an intermediary material mixed with SVO cathode active material. This CFx layer acts as a protective intermediary that prevents direct contact between the electrolyte and vanadium ions in SVO, thereby eliminating vanadium ion dissolution into the electrolyte while maintaining high conductivity. The CFx forms a stable interface that mediates between the electrolyte and cathode materials.
Solution Approach 2:
The patent creates a composite cathode material by mixing SVO and CFx in specific ratios (e.g., 90:10 to 50:50 by weight). This composite structure combines the high conductivity and voltage delay reduction properties of CFx with the electrochemical activity of SVO, achieving both high reliability and elimination of harmful vanadium ion dissolution effects.
2Reliability
If the electrolyte composition is optimized for high conductivity (e.g., PC:DME ratio), then conductivity is improved, but stability toward cathode materials deteriorates
Solution Approach 1:
The patent optimizes the PC:DME volume ratio parameter in the electrolyte to achieve a balance between conductivity and stability. By adjusting this compositional parameter to specific ranges, the electrolyte maintains high conductivity while improving stability toward cathode materials, preventing decomposition and extending cell life.
Solution Approach 2:
The patent applies different functional requirements to different parts of the cathode structure. The CFx component provides local stability and protection at the electrolyte-cathode interface, while the SVO component maintains electrochemical activity. This local differentiation of properties allows the system to achieve both high conductivity and stability simultaneously.
3Power
If high rates of discharge are required for implantable medical devices, then power density is improved, but voltage delays and performance instability worsen
Solution Approach 1:
The CFx material serves as a mediator that enables high power density discharge while maintaining performance stability. It facilitates rapid electron transfer for high power output while simultaneously preventing vanadium ion dissolution that would cause voltage delays and instability during high-rate discharge operations.
Solution Approach 2:
The SVO/CFx composite cathode material combines the high power density capability of SVO with the stability and voltage delay reduction properties of CFx. This composite structure enables the cell to deliver high power density required by implantable medical devices while maintaining stable performance throughout discharge cycles.
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 new electrolyte system significantly reduces voltage delays, enhances conductivity, and improves the energy and power density of lithium electrochemical cells, particularly in high-rate discharge applications, ensuring stable performance for implantable medical devices.
Implementation Method 1
a nonaqueous, ionically conductive electrolyte which serves as a medium for migration of ions between the anode and the cathode during electrochemical reactions of the cell
Implementation Method 2
conversion of chemical energy to electrical energy
Data Source
AI summary
An electrochemical cell having a casing housing an electrode assembly of a separator residing between a lithium anode and a cathode comprising silver vanadium oxide and fluorinated carbon is described. The electrode assembly is activated with a nonaqueous electrolyte comprising a lithium salt dissolved in a solvent system of propylene carbonate mixed with 1,2-dimethoxyethane, dibenzyl carbonate (DBC), lithium bis(oxalato)borate (LiBOB), and fluoroethylene carbonate (FEC). Preferably DBC is present in an amount ranging from about 0.005 moles (M) to about 0.25M, LiBOB is present in an amount ranging from about 0.005 wt. 5 to about 5 wt. %, and FEC is present in an amount ranging from about 0.01 wt. % to about 10 wt. %. This electrolyte formulation is more conductive than the conventional or prior art binary and ternary solvent system electrolytes while being chemically and electrochemically stable toward Li/SVO cells, Li-SVO/CFx mixture cells, and Li-SVO/CFx sandwich cathode primary electrochemical cells.