LiBOB and FEC Additives in PC-DME Electrolyte for Lithium-SVO Cells
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Solution Overview
Problem
Conventional nonaqueous organic electrolytes used in lithium electrochemical cells, such as those with a propylene carbonate (PC) and dimethoxyethane (DME) solvent system, face challenges in achieving high conductivity while maintaining stability, leading to voltage delays due to vanadium ion dissolution and impedance build-up, which affects the performance of high-rate lithium primary cells powering implantable medical devices.
Innovation Solution
A new electrolyte system comprising lithium hexafluoroarsenate (LiAsF6) dissolved in a solvent mixture of propylene carbonate (PC) and dimethoxyethane (DME) with lithium bis(oxalato)borate (LiBOB) and fluoroethylene carbonate (FEC) additives, optimizing the volume ratio and concentrations to enhance conductivity and stability, thereby reducing voltage delays and improving energy and power density.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional nonaqueous organic electrolytes (PC:DME solvent system) are used to achieve high conductivity, then electrolyte conductivity is improved, but voltage delays occur due to vanadium ion dissolution and impedance build-up
Solution Approach 1:
The patent introduces LiBOB and FEC as intermediary substances that mediate between the electrolyte and electrode materials. These additives form protective interface layers that prevent direct harmful interactions between the PC:DME electrolyte and electrode materials, thereby eliminating voltage delays while preserving high conductivity
Solution Approach 2:
The patent modifies the electrolyte composition by adding specific concentrations of LiBOB (0.01-5% by weight) and FEC (0.01-10% by weight) to the PC:DME solvent system. This parameter change transforms the electrolyte's interfacial properties, preventing vanadium ion dissolution and impedance build-up without sacrificing conductivity
2Reliability
If the volume ratio of PC to DME is optimized for higher conductivity (less than 50:50), then electrolyte conductivity is improved, but stability toward cathode active material deteriorates
Solution Approach 1:
LiBOB and FEC act as intermediary protective agents that stabilize the electrolyte-cathode interface. They form stable surface films that prevent direct contact between the electrolyte and cathode materials, thereby maintaining electrolyte stability even when the PC:DME ratio is optimized for maximum conductivity
Solution Approach 2:
The patent creates a composite electrolyte system combining PC, DME, LiBOB, and FEC. This composite formulation leverages the high conductivity of PC:DME while the LiBOB and FEC components provide stabilizing functions, achieving both high conductivity and stability simultaneously
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, increases energy and power density, and provides improved long-term stability for lithium-SVO and lithium-SVO/CFx mixture cells, enhancing their performance in high-rate discharge applications for implantable medical devices.
Implementation Method 1
A nonaqueous, ionically conductive electrolyte is provided which serves as a medium for migration of ions between the anode and cathode during electrochemical reactions of the cell
Implementation Method 2
The assembly of the cells is then filled with the electrolyte solution described above and hermetically sealed. The electrochemical cell contains a lithium or lithium alloy anode, a cathode containing silver vanadium oxide (SVO) or manganese dioxide (MnO2)
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, lithium bis(oxalato)borate (LiBOB), and fluoroethylene carbonate (FEC). Preferably 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.