Silicon-Based Alloy Negative Electrode with Porosity Control
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Solution Overview
Problem
Lithium secondary batteries face challenges with the swelling and shrinking of silicon-based negative active materials during charging and discharging, leading to cracked surfaces and reduced cycle characteristics, as well as high internal porosity in alloys which can result in side reactions with the electrolyte, decreasing battery performance.
Innovation Solution
A silicon-based alloy with a porosity of 24% to 35% is developed, incorporating additional elements like carbon, boron, or oxygen both within the alloy and on its surface, which acts as a buffer to mitigate volume changes and reduce side reactions, thereby enhancing the capacity and lifespan of lithium batteries.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If silicon-based alloy is used as negative active material, then capacity is improved, but volume expansion and surface cracking occur during charging and discharging
Solution Approach 1:
A carbon coating layer is applied on the surface of the silicon-based alloy particles. This carbon shell acts as a flexible protective layer that accommodates volume expansion during lithiation while maintaining surface integrity and preventing particle cracking during delithiation.
Solution Approach 2:
The negative active material uses a composite structure combining silicon-based alloy with carbon material. The silicon provides high capacity while the carbon matrix provides structural stability and conductivity, creating a synergistic composite that resolves the contradiction between capacity and stability.
2Stability of the object's composition
If high internal porosity is present in silicon-based alloy, then volume expansion is accommodated, but side reactions with electrolyte increase
Solution Approach 1:
The carbon coating layer forms a protective shell that seals the porous internal structure of the silicon-based alloy. This shell allows the internal porosity to accommodate volume changes while preventing direct contact between the electrolyte and the silicon surface, thereby reducing side reactions.
Solution Approach 2:
The carbon coating acts as an intermediary layer between the silicon-based alloy and the electrolyte. It mediates the interaction by allowing ion transport while preventing harmful direct contact, thus enabling volume expansion accommodation without increasing side reactions.
3Stability of the object's composition
If carbon coating is applied on silicon-based alloy, then surface stability is improved, but initial efficiency decreases
Solution Approach 1:
The thickness of the carbon coating is optimized to a specific range (0.5-5 nm) to balance surface stability and initial efficiency. This parameter optimization ensures sufficient protection against cracking while maintaining adequate lithium ion diffusion pathways and electrical conductivity for high initial efficiency.
Solution Approach 2:
The carbon coating is applied as a thin, uniform layer that provides localized protection exactly where needed on the particle surface. This localized approach maintains surface stability without excessive material that would impede ion transport and reduce initial efficiency.
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 silicon-based alloy with controlled porosity and surface elements improves the cycle characteristics and lifespan of lithium batteries by suppressing volume expansion and side reactions, maintaining initial efficiency and reducing electrolyte permeability.
Implementation Method 1
the additional element (A) is included in the silicon-based alloy and disposed on surfaces of the silicon-based alloy... acts as a buffer to mitigate volume changes
Implementation Method 2
Lithium secondary batteries produce electrical energy by way of oxidization or reduction reactions which occur during intercalation and deintercalation of lithium ions
Implementation Method 3
produce electrical energy by way of oxidization or reduction reactions
Implementation Method 4
produce electrical energy by way of oxidization or reduction reactions
Data Source
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AI summary
A negative active material includes a silicon-based alloy, wherein the silicon-based alloy includes silicon (Si); a first metal (M1) selected from aluminium (Al), titanium (Ti), vanadium (V), chromium (Cr), iron (Fe), cobalt (Co), nickel (Ni), copper (Cu), zinc (Zn), gallium (Ga), and germanium (Ge), and at least one additional element (A), which is included in the silicon-based alloy and on a surface of silicon-based alloy, selected from carbon (C), boron (B), sodium (Na), nitrogen (N), phosphorous (P), sulfur (S), and chlorine (Cl), and the silicon-based alloy has an internal porosity of about 35% or less. A lithium battery including the negative active material may have improved lifespan characteristics.