Lithium Fluorosilicate Anode for Battery Cycle Life
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Solution Overview
Problem
Lithium ion secondary batteries using silicon as the anode active material face issues with volume expansion and pulverization during charge and discharge cycles, leading to reduced cycle characteristics and capacity, as well as electrolyte decomposition due to high reactivity.
Innovation Solution
The use of an anode active material layer containing LixSiFy (1≦x≦2 and 5≦y≦6) on an anode current collector, where lithium fluorosilicate (Li2SiF6) is employed to inhibit volume expansion and improve lithium insertion and extraction, while a fluorine-containing compound like polyvinylidene fluoride is added to prevent electrolyte decomposition.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If silicon is used as the anode active material to increase battery capacity, then the theoretical capacity is significantly improved, but the anode active material layer is easily pulverized due to intense expansion and shrinkage during charge and discharge
Solution Approach 1:
The patent uses a composite material structure where silicon particles are embedded in a carbon matrix. The carbon matrix provides structural stability and prevents pulverization during expansion and shrinkage, while silicon provides high capacity. This composite approach resolves the contradiction by combining the high capacity advantage of silicon with the structural stability of carbon.
Solution Approach 2:
The patent employs a flexible carbon coating layer surrounding silicon particles. This thin film structure allows for volume expansion and contraction of the silicon core while maintaining structural integrity and preventing particle pulverization. The flexible carbon shell accommodates the mechanical stress during charge-discharge cycles.
2Quantity of substance
If silicon is used as the anode active material to increase battery capacity, then the theoretical capacity is significantly improved, but decomposition of the electrolytic solution easily occurs due to high reactivity
Solution Approach 1:
The patent introduces a carbon coating layer as an intermediary between silicon and the electrolyte. This intermediate layer reduces the direct contact and high reactivity between silicon and electrolyte, preventing decomposition while still allowing lithium ion transport. The carbon layer acts as a protective barrier that mediates the interaction between the reactive silicon and the electrolyte.
Solution Approach 2:
The carbon coating creates an inert environment around the silicon particles, isolating them from the electrolyte. This inert carbon layer prevents harmful chemical reactions and electrolyte decomposition while maintaining the electrochemical functionality of the silicon anode material.
3Reliability
If the anode active material layer is made to accommodate volume changes to improve cycle life, then structural stability is improved, but the battery capacity and energy density are reduced
Solution Approach 1:
The patent applies different materials with different properties to different parts of the anode structure. The silicon core provides high capacity in the central region, while the carbon matrix and coating provide structural stability in the surrounding regions. This local differentiation of material properties allows simultaneous optimization of capacity and cycle life.
Solution Approach 2:
The composite structure combines silicon (high capacity) with carbon (structural stability). The carbon component accommodates volume changes and provides structural framework, while the silicon component maintains high capacity. This composite approach resolves the capacity-stability trade-off by distributing different functions to different materials within the same structure.
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 enhances the cycle characteristics and capacity of lithium ion secondary batteries by reducing structural breakage and maintaining high energy density, with improved stability and reduced micro-short circuits.
Implementation Method 1
lithium fluorosilicate (Li2SiF6) is employed to inhibit volume expansion and improve lithium insertion and extraction
Implementation Method 2
improve lithium insertion and extraction, while a fluorine-containing compound like polyvinylidene fluoride is added to prevent electrolyte decomposition
Implementation Method 3
a fluorine-containing compound like polyvinylidene fluoride is added to prevent electrolyte decomposition
Data Source
AI summary
A lithium secondary battery that has high capacity and excellent cycle characteristics is provided. The lithium ion secondary battery includes a cathode, an anode, and an electrolyte. The anode has, on an anode current collector, an anode active material layer including LixSiFy (1≦x≦2 and 5≦y≦6) as an anode active material.