Separator Coating for Si-Based Lithium Batteries at High Temperature
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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 from 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
1Reliability
If heat-resistant inorganic particles are coated on the separator to improve thermal stability, then battery stability at high temperature is improved, but adherence between the separator and electrode deteriorates due to reduced binder content
Solution Approach 1:
The patent changes the chemical composition parameters of the coating layer by introducing fluorine-based polymers and specific inorganic compounds (Al2O3, MgO, TiO2, Al(OH)3, Mg(OH)2, Ti(OH)4) with defined weight ratios. This parameter optimization allows the coating layer to maintain both thermal resistance and adherence properties simultaneously, resolving the contradiction between stability and adherence.
Solution Approach 2:
The patent creates a composite coating layer combining fluorine-based polymers with multiple inorganic compounds in specific proportions. This composite structure provides both the thermal stability from inorganic particles and the adherence from the fluorine-based polymer matrix, eliminating the need to compromise binder content while maintaining bonding strength.
2Temperature
If the amount of heat-resistant inorganic particle is increased to improve thermal stability, then battery stability is improved, but the amount of binder is decreased leading to poor adherence
Solution Approach 1:
The patent optimizes the weight ratio parameters of inorganic compounds to fluorine-based polymer within 90:10 to 10:90, with specific embodiments at 80:20, 70:30, 60:40, 50:50, 40:60, 30:70, and 20:80. This parameter range ensures sufficient inorganic content for heat resistance while maintaining adequate fluorine-based polymer for adherence, resolving the contradiction between temperature resistance and bonding strength.
3Reliability
If separator coating is applied to prevent short circuit from electrode contraction, then battery stability is improved, but manufacturing complexity increases
Solution Approach 1:
The patent employs a porous substrate as the separator base material, which inherently provides ion transport pathways and structural flexibility. The coating layer is applied on this porous structure, maintaining the essential battery functions while adding thermal and mechanical stability, thus achieving reliability improvement without excessive complexity.
Solution Approach 2:
The patent creates a composite structure combining a porous substrate with a coating layer containing fluorine-based polymer and inorganic compounds. This composite approach provides the necessary stability functions (thermal resistance, contraction prevention, adherence) through material composition rather than complex structural design, minimizing manufacturing complexity while achieving reliability goals.
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
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 has been suggested
Implementation Method 3
pores of the film are filled with an electrolyte solution in which a lithium salt is dissolved
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.