Separator Coating for Si-Based Lithium Battery Cycle Stability
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Solution Overview
Problem
Rechargeable lithium batteries face issues with adherence between the separator and electrodes, leading to potential short circuits due to temperature increases during exothermic reactions and repeated charge-discharge cycles, which compromise stability and cycle-life characteristics.
Innovation Solution
A rechargeable lithium battery design incorporating a separator with a coating layer containing a fluorine-based polymer and inorganic compounds on a porous substrate, using specific non-aqueous organic solvents and additives to enhance adherence and stability, including a Si-based negative active material and a lithiated intercalation compound positive active material.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If the amount of heat-resistant inorganic particle is increased in the coating layer, then thermal stability is improved, but the amount of binder is decreased and adherence between separator and electrode deteriorates
Solution Approach 1:
The patent changes the chemical composition parameters of the coating layer by introducing a fluorinated polymer as binder and controlling the weight ratio of inorganic particles to coating layer (90:10 to 99:1). This parameter optimization allows sufficient inorganic content for thermal stability while maintaining adequate binder for adherence.
Solution Approach 2:
The patent creates a composite coating layer combining fluorinated polymer binder with inorganic particles (such as alumina, silica, or titania). This composite structure integrates the thermal stability of inorganic materials with the adhesive properties of the fluorinated polymer, resolving the contradiction between thermal performance and adherence.
2Temperature
If the separator is coated with heat-resistant inorganic particles and binder, then stability at high temperature is improved, but the complexity of manufacturing increases
Solution Approach 1:
The coating layer is applied to the separator surface before battery assembly, forming a pre-prepared thermal protection layer. This preliminary action ensures high-temperature stability is built into the separator structure beforehand, simplifying the overall manufacturing process by eliminating the need for post-assembly thermal treatment.
Solution Approach 2:
The patent uses a thin film coating layer (comprising fluorinated polymer and inorganic particles) on the separator surface. This thin film approach provides high-temperature stability without significantly increasing separator thickness or manufacturing complexity, as the coating can be applied using standard coating techniques.
3Reliability
If a coating layer with inorganic particles and binder is applied to the separator, then storability at high temperature is improved, but the device complexity increases
Solution Approach 1:
The patent applies the coating layer with fluorinated polymer and inorganic particles specifically on the surface of the separator where it contacts the electrodes. This localized application provides high-temperature storability at the critical interface regions without requiring the entire separator structure to be complex, maintaining simplicity in the bulk separator material.
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 improves adherence between the separator and electrodes, ensuring stability, high-temperature storability, and extended cycle-life characteristics by preventing sharp contraction and deformation during charge-discharge cycles.
Implementation Method 1
when the positive and the negative electrodes in the battery are repeatedly contracted and expanded during charge and discharge cycles, a battery temperature may be sharply increased. As a result, the separator may become contracted along with the electrodes or altogether destroyed
Implementation Method 2
pores of the film are filled with an electrolyte solution in which a lithium salt is dissolved
Implementation Method 3
a method of coating the separator with a heat-resistant inorganic particle along with a binder on at least one side to secure stability of the battery
Data Source
AI summary
Disclosed is a rechargeable lithium battery including a positive electrode including a positive active material; a negative electrode including a negative active material; an electrolyte solution including a lithium salt and a non-aqueous organic solvent; and a separator between the positive and the negative electrodes, the separator including a porous substrate and a coating layer positioned on at least one side of the porous substrate. The negative active material includes a Si-based material; the non-aqueous organic solvent includes cyclic carbonate including ethylene carbonate, propylene carbonate, or combinations thereof, the cyclic carbonate being included in an amount of about 20 volume % to about 60 volume % based on the total amount of the non-aqueous organic solvent; and the coating layer includes a fluorine-based polymer, an inorganic compound, or combinations thereof. The rechargeable lithium battery has improved cycle-life and high temperature storage characteristics.