Silicon-Carbon Negative Electrode SEI Stability
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Solution Overview
Problem
Lithium secondary batteries using silicon-based compounds as negative electrodes face rapid capacity degradation and reduced cycle life due to large volume expansion and contraction, leading to electrical short circuits and physical destruction of the solid electrolyte interphase (SEI).
Innovation Solution
A lithium secondary battery design incorporating a negative electrode with a carbon-based material and a silicon-based compound, paired with a non-aqueous electrolyte solution containing LiPF6, LiN(FSO2)2, and a solvent mixture of fluorine-based cyclic and linear carbonate organic solvents, which forms a robust SEI to prevent physical destruction and increase in contact resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If silicon-based compound is used as negative electrode active material to increase capacity, then battery capacity is improved, but volume expansion and contraction during charge and discharge causes physical destruction of SEI and electrical short circuit
Solution Approach 1:
The patent uses a composite structure where silicon-based active material particles are embedded in a porous carbon matrix. This composite design allows the silicon to expand and contract during lithium insertion/extraction while the carbon matrix provides structural support and prevents particle disintegration, thereby maintaining both high capacity and long cycle life
Solution Approach 2:
The porous carbon coating acts as a flexible shell around the silicon particles. This thin film structure accommodates the volume changes of silicon during charge-discharge cycles, preventing mechanical failure of the SEI layer and maintaining electrical contact between active material particles and current collector
2Use of energy by moving object
If silicon-based active material is used to achieve high capacity, then energy density is improved, but contact resistance between particles increases due to SEI destruction
Solution Approach 1:
The porous carbon coating serves as a protective shell that maintains electrical contact between silicon particles and the current collector even during volume expansion and contraction. This prevents the increase in contact resistance that would otherwise occur due to SEI layer destruction
Solution Approach 2:
The porous carbon matrix acts as an intermediary between the silicon particles and the electrolyte/SEI layer. It provides a stable interface that maintains electrical conductivity while allowing lithium ion transport, thereby preventing contact resistance increase without compromising energy density
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 solution enhances the cycle characteristics of lithium secondary batteries by forming a stable SEI, reducing capacity loss and resistance increase, and improving the battery's durability and energy density.
Implementation Method 1
a robust solid electrolyte interphase (SEI) capable of suppressing physical destruction is formed on a surface of a negative electrode by using an non-aqueous electrolyte solution, which contains two types of lithium salts containing a fluorine component and a fluorine-based carbonate organic solvent
Implementation Method 2
since large volume expansion and contraction occur due to a reaction with lithium during charge and discharge
Data Source
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AI summary
The present invention relates to a lithium secondary battery which includes a positive electrode, a negative electrode including a carbon-based material and a silicon-based compound, a non-aqueous electrolyte solution containing LiPF6, LiN(FSO2)2, and a non-aqueous organic solvent, and a separator, wherein a fluorine-based cyclic carbonate organic solvent and a fluorine-based linear carbonate organic solvent are included as the non-aqueous organic solvent.