Crystalline Silicon Anode with Mixed Particle Morphology
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Solution Overview
Problem
Lithium ion secondary batteries using silicon as an anode active material face challenges in maintaining cycle characteristics and swollenness due to the amorphous nature of silicon deposits, leading to electrolyte decomposition, physical property deterioration, and potential detachment of the anode active material layer from the current collector.
Innovation Solution
The anode active material layer is composed of crystalline silicon particles with a mixture of spherical and nonspherical particles, bonded with metal elements and oxygen, which are deposited on a roughened copper current collector to enhance mechanical stability and prevent expansion and shrinkage during charge and discharge cycles.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If silicon is directly deposited on the anode current collector using vapor-phase deposition method, then the anode active material is fixed on the current collector, but the anode active material layer is hardly expanded and shrunk at charge and discharge, leading to electrolyte decomposition and poor cycle characteristics
Solution Approach 1:
The invention changes the physical state parameter of silicon from amorphous to crystalline. By controlling the deposition process to form crystalline silicon particles instead of amorphous silicon film, the material maintains its ability to expand and shrink during lithium ion insertion and extraction, thereby preventing electrolyte decomposition and improving cycle characteristics
Solution Approach 2:
The invention creates a composite structure where crystalline silicon particles are dispersed in a carbon-containing substance matrix. This composite material combines the high capacity of silicon with the structural stability and conductivity of carbon, allowing the silicon particles to expand and shrink without detaching from the current collector while maintaining good electrochemical performance
2Strength
If silicon is directly deposited on the anode current collector, then the anode active material is linked to the current collector, but the anode active material layer may be broken and dropped after repeated charge and discharge
Solution Approach 1:
The carbon-containing substance acts as a flexible matrix that can accommodate the volume changes of silicon particles during charge and discharge. This carbon shell or matrix envelops the silicon particles, providing mechanical support and preventing them from breaking off and detaching from the current collector, thus maintaining discharge capacity retention
Solution Approach 2:
The composite structure of crystalline silicon particles dispersed in carbon-containing substance provides both strong adhesion to the current collector and internal flexibility to handle volume expansion/contraction. The carbon matrix bonds the silicon particles together and to the substrate, preventing layer detachment while allowing reversible structural changes
3Productivity
If silicon is directly deposited on the anode current collector, then the anode active material layer is formed, but the anode current collector becomes easily deformed due to intense expansion and shrinkage
Solution Approach 1:
The carbon-containing substance forms a flexible matrix that absorbs and distributes the mechanical stress generated by silicon expansion and shrinkage. This carbon shell acts as a buffer layer that protects the rigid current collector from deformation while still allowing the silicon particles to undergo their necessary volume changes for high capacity
Solution Approach 2:
The composite structure distributes the mechanical load across the carbon matrix rather than concentrating it on the current collector. The carbon-containing substance serves as a compliant intermediate layer that decouples the silicon's volume changes from the current collector, preventing deformation while maintaining structural integrity
4Ease of manufacture
If amorphous silicon depositional film is used, then the anode active material is formed, but the anode active material is easily affected by oxidation and physical property deteriorates with age
Solution Approach 1:
The invention fundamentally changes the structural parameter of silicon from amorphous to crystalline. Crystalline silicon has a more stable atomic arrangement that is less susceptible to oxidation and physical degradation over time. The crystalline structure maintains its integrity during repeated charge and discharge cycles, preserving the anode's physical properties and electrochemical performance
Solution Approach 2:
The carbon-containing substance matrix provides a protective environment for the crystalline silicon particles, further shielding them from oxidation. The composite structure combines the chemical stability of crystalline silicon with the protective and conductive properties of carbon, resulting in an anode material that maintains its physical properties over extended periods
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 improves the cycle characteristics and swollenness of the battery by maintaining the physical properties of the anode active material, reducing electrolyte decomposition, and preventing detachment of the anode active material layer, resulting in superior performance and extended battery life.
Implementation Method 1
an anode active material layer capable of inserting and extracting an electrode reactant on an anode current collector
Implementation Method 2
as a method of forming the anode active material layer, vapor-phase deposition method such as evaporation method is used. In this case, silicon is directly deposited on the surface of the anode current collector
Data Source
AI summary
A secondary battery capable of obtaining superior cycle characteristics and superior swollenness characteristics is provided. The secondary battery includes a cathode and an anode capable of inserting and extracting an electrode reactant; and an electrolyte containing a solvent and an electrolyte salt. The anode has an anode active material layer on an anode current collector. The anode active material layer contains a plurality of crystalline anode active material particles having silicon (Si) as an element. The plurality of anode active material particles contain a spherical particle and a nonspherical particle.