Hybrid Cathode Design for High Capacity Lithium Cells
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Solution Overview
Problem
Primary lithium/SO2 cells have limited capacity and energy density due to the reactive nature of metallic lithium, which can lead to undesirable reactions with the solvent and cathode material, resulting in reduced cell performance and potential cell rupture.
Innovation Solution
Incorporating a solid cathode material with a higher electromotive force (EMF) than the liquid SO2 cathode, such as MnO2 or CFX, into the cell to create a hybrid cathode configuration, which balances the EMF ratio and prevents excessive lithium reaction with the solvent, thereby increasing capacity and energy density.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If a liquid SO2 cathode is used in a primary lithium cell, then the cell can achieve a certain discharge capacity, but the reactive nature of metallic lithium causes it to spontaneously react with the SO2 and solvent, forming a SEI film that limits further reactions and reduces cell capacity
Solution Approach 1:
The cathode is segmented into two distinct components: a liquid SO2 cathode and a solid cathode material with higher EMF. This segmentation allows the solid cathode to act as a preferential reaction site, preventing lithium from reacting with the liquid SO2 and solvent, thereby eliminating the harmful SEI formation while maintaining discharge capacity through the liquid component.
2Power
If the cell uses only liquid SO2 cathode, then the EMF is limited to about 3.1V, but increasing the amount of lithium to increase capacity leads to excessive reactions with solvent and cathode material
Solution Approach 1:
The cathode uses a composite structure combining liquid SO2 and solid cathode material. The solid component provides higher EMF (3.45V for CFX), while the liquid component contributes to capacity. This composite approach achieves both higher voltage and increased capacity without the harmful side reactions that occur when using only liquid SO2 with excess lithium.
3Reliability
If excess SO2 is used to prevent lithium reaction with solvent, then the capacity ratio of lithium to SO2 must be maintained, but this limits the maximum capacity of the cell
Solution Approach 1:
The solid cathode material acts as an intermediary that preferentially reacts with lithium, protecting the liquid SO2 and solvent from excessive lithium consumption. This intermediary role allows the cell to use optimal lithium-to-SO2 ratios without the need for excess SO2, thereby increasing capacity while maintaining reliability and preventing cell rupture.
4Use of energy by moving object
If a solid cathode material with higher EMF is incorporated into the cell, then the energy density increases, but the cell structure becomes more complex with hybrid cathode configuration
Solution Approach 1:
The invention merges the liquid SO2 cathode and solid cathode material into a single hybrid cathode structure that functions as one integrated electrochemical system. This merging approach increases energy density through the high EMF solid material while maintaining manageable structural complexity, as both components work together in a unified cathode assembly rather than requiring separate systems.
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 hybrid cell design significantly enhances the discharge capacity and energy density beyond standard Li/SO2 cells, preventing lithium reaction with the solvent and maintaining cell integrity, while maintaining a stable voltage profile during discharge.
Implementation Method 1
During the cell's discharge the liquid cathode transfers the electricity to a porous high surface area conductive current collector
Implementation Method 2
Inside the cell, the lithium ions move from the anode side to the cathode side to naturalize the charge
Implementation Method 3
The anode is oxidized to lithium ions while the cathodic material is reduced and changes its valence to a lower state
Implementation Method 4
the cathodic material is reduced and changes its valence to a lower state
Implementation Method 5
The electrolyte of the Li/SO2 and the Li/MnO2 systems contains lithium salts that are dissolves in an organic solvent or a mixture of organic solvents to form a conducting solution that conducts the electricity inside the cell
Implementation Method 6
the electrolyte typically includes acetonitrile (AN) as a solvent and Lithium bromide (LiBr) as the ionizable salt
Implementation Method 7
the metallic lithium anode spontaneously reacts with SO2 to form a Li2SO2O4 film that is precipitated on the anode and is known as a solid electrolyte interphase (SEI). The SEI prevents further reaction of the SO2 with the lithium anode
Implementation Method 8
Incorporating a solid cathode material with a higher electromotive force (EMF) than the liquid SO2 cathode, such as MnO2 or CFX, into the cell to create a hybrid cathode configuration, which balances the EMF ratio and prevents excessive lithium reaction with the solvent
Data Source
AI summary
A high capacity primary electrochemical lithium cell includes an anode comprising metallic lithium, a hybrid cathode comprising a liquid SO2 cathode and a solid cathode including a cathode material characterized by having a first electromotive force (EMF) when coupled to a metallic lithium anode. The first EMF is greater than a second EMF of a cell having a metallic lithium anode and a liquid SO2 cathode. A separator may separate the anode from the solid cathode. The cell includes an electrolyte solution including at least one ionizable salt dissolved in at least one organic solvent. The solid cathode material may include carbon monofluoride (CFX), a transition metal oxide, a mixture of two or more transition metal oxides or any combinations of such cathode materials. The solid cathode may also include a binder and a carbon based conductive material.