Silicon-Anode Electrolyte Ratio for Stable SEI and Low Resistance
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Solution Overview
Problem
The challenge is to improve the energy density of electrochemical apparatuses, such as lithium-ion batteries, by addressing the volume change and conductivity issues of silicon materials used as negative electrodes, which lead to SEI film splitting and increased direct current resistance.
Innovation Solution
The use of an electrolyte comprising fluoroethylene carbonate and non-fluorinated cyclic carbonate, with a specific mass ratio, along with a conductive layer and a protective layer on the silicon-containing material, helps to maintain the stability of the SEI film, reduce direct current resistance, and enhance cycling performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If silicon material is used as negative electrode material to improve energy density, then theoretical capacity is greatly improved, but volume changes during lithium intercalation and deintercalation cause SEI film splitting and cycling degradation
Solution Approach 1:
The patent applies parameter changes by precisely controlling the mass ratio of fluoroethylene carbonate to non-fluorinated cyclic carbonate in the electrolyte within 0.05≤a/b≤2.5. This parameter optimization ensures the electrolyte can effectively repair the SEI film while maintaining low viscosity and good conductivity, resolving the contradiction between capacity improvement and cycling stability
Solution Approach 2:
The patent introduces the electrolyte composition as an intermediary substance that mediates between the silicon material and the external environment. The specific ratio of fluoroethylene carbonate to non-fluorinated cyclic carbonate creates a protective SEI film that acts as a buffer, absorbing volume expansion stress and preventing direct contact between the electrolyte and silicon material surface during cycling
2Reliability
If fluoroethylene carbonate is added to repair SEI film and improve cycling performance, then cycling performance is improved, but viscosity of the electrolyte increases and conductivity decreases
Solution Approach 1:
The patent applies parameter changes by optimizing the mass percentage of fluoroethylene carbonate in the electrolyte to be within 3≤a≤25%, and controlling the ratio a/b within 0.05≤a/b≤2.5. This precise parameter control ensures sufficient SEI film repair capability while preventing excessive viscosity increase and conductivity loss
Solution Approach 2:
The patent creates a composite electrolyte system by combining fluoroethylene carbonate with non-fluorinated cyclic carbonate in specific proportions. This composite approach leverages the SEI film repair capability of fluoroethylene carbonate while using non-fluorinated cyclic carbonate to maintain low viscosity and high conductivity, achieving a balance between cycling performance and energy loss
3Quantity of substance
If mass of silicon element per unit coating area is increased to improve specific capacity, then specific capacity is increased, but volume swelling during cycling increases causing SEI film splitting
Solution Approach 1:
The patent applies parameter changes by optimizing the mass of silicon element per unit coating area to be within 0.1≤X≤1.3 mg/cm2. This parameter optimization ensures sufficient specific capacity while limiting excessive volume swelling that would cause SEI film splitting during cycling
Solution Approach 2:
The electrolyte composition acts as an intermediary that compensates for the instability caused by high silicon content. The optimized ratio of fluoroethylene carbonate to non-fluorinated cyclic carbonate enables the electrolyte to continuously repair the SEI film on high-silicon negative electrodes, maintaining film stability even when silicon content is increased for higher capacity
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
This configuration results in improved cycling performance and reduced direct current resistance, maintaining the energy density and stability of the electrochemical apparatus while preventing excessive volume swelling and conductivity loss.
Implementation Method 1
a fluoroethylene carbonate content a (%) and a non-fluorinated cyclic carbonate content b (%) in the electrolyte satisfy 0.05≤a/b≤2.5... the fluoroethylene carbonate can continuously repair the SEI film of the negative electrode material in cycling
Implementation Method 2
a volume of the silicon material greatly changes during a lithium intercalation and deintercalation process... lithium intercalation and deintercalation is continuously performed on the silicon material
Data Source
AI summary
An electrochemical apparatus, including a positive electrode, a negative electrode, and an electrolyte, where the electrolyte includes fluoroethylene carbonate and non-fluorinated cyclic carbonate, the fluoroethylene carbonate accounts for a % of the electrolyte by mass, and the non-fluorinated cyclic carbonate accounts for b % of the electrolyte by mass, where 0.05≤a/b≤2.5.