Silicon Negative Electrode Pre-Lithiation for Lower Initial Irreversibility
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Solution Overview
Problem
Lithium secondary batteries face issues with initial irreversibility and capacity loss due to the formation of the solid electrolyte interface (SEI) layer, particularly with silicon-based negative electrode active materials, which experience volume expansion and side reactions with the electrolyte solution, leading to increased resistance and reduced cycle lifespan.
Innovation Solution
A negative electrode for lithium secondary batteries is developed with a silicon-based active material that undergoes pre-lithiation to a specific extent (5-50%), where lithium metal powder is coated, pressed, and then wetted with an electrolyte solution to form a stable passivation layer, reducing side reactions and enhancing cycle characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If silicon-based negative electrode active material is used to increase capacity, then battery capacity is improved, but volume expansion rate increases to 300% or more causing electrode structure damage
Solution Approach 1:
The patent embeds silicon-based active material particles inside a porous carbon matrix structure. The carbon matrix acts as a container that accommodates the silicon particles, allowing the high-capacity silicon to be protected while maintaining structural integrity during volume expansion cycles.
Solution Approach 2:
The patent employs a flexible porous carbon matrix that can expand and contract with the silicon particles during lithium insertion/extraction cycles. This flexible structure accommodates the 300% volume expansion of silicon without causing electrode disintegration, while maintaining electrical conductivity and structural stability.
2Quantity of substance
If pre-lithiation is performed to reduce initial irreversibility, then initial capacity loss is reduced, but by-products are generated and lithium oxide is produced only on the surface
Solution Approach 1:
The patent removes oxygen from the silicon-based active material before battery assembly through vacuum drying processes. This extraction of oxygen prevents the formation of lithium oxide by-products during initial charging cycles, eliminating the harmful side reactions while still allowing controlled pre-lithiation to occur.
Solution Approach 2:
The patent performs preliminary lithium intercalation into the silicon-based active material during the coating process, before battery assembly. This preliminary action of adding lithium reduces the initial irreversibility and SEI layer formation issues during first charging, while the controlled amount prevents excessive by-product generation.
3Quantity of substance
If lithium metal thin film is pressed on negative electrode surface for pre-lithiation, then initial irreversibility is reduced, but lithium oxide is produced only on surface limiting irreversibility reduction
Solution Approach 1:
The patent creates local lithium-rich zones within the silicon-based active material particles through controlled lithium intercalation during coating. This local quality enhancement ensures that lithium is available where needed (inside the particles) rather than only on the surface, enabling uniform reduction of initial irreversibility throughout the entire electrode structure.
4Quantity of substance
If silicon-based material is used to achieve high capacity, then effective capacity increases 10 times compared to carbon-based material, but side reactions with electrolyte solution increase resistance
Solution Approach 1:
The patent uses a sacrificial porous carbon matrix that provides initial protection during the first few cycles. This carbon matrix acts as a temporary protective layer that sacrifices itself to form a stable SEI layer, preventing direct contact between the silicon-based active material and the electrolyte solution during subsequent cycles, thereby reducing side reactions and resistance increase.
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 approach effectively reduces gas generation from side reactions, improves capacity retention, and extends the battery's cycle life by forming a uniform passivation layer, thereby enhancing the battery's performance and preventing electrode structure damage.
Implementation Method 1
a negative electrode active material layer which is formed on the negative electrode current collector and includes a negative electrode active material including a silicon-based material, wherein the negative electrode active material includes lithium intercalated by pre-lithiation
Implementation Method 2
since a solid electrolyte interface (SEI) layer is formed on the surface of the negative electrode active material during initial charging/discharging (activation)
Data Source
AI summary
The present invention provides a negative electrode for a lithium secondary battery, which includes a negative electrode current collector; and a negative electrode active material layer which is formed on the negative electrode current collector and includes a negative electrode active material including a silicon-based material, wherein the negative electrode active material includes lithium intercalated by pre-lithiation, and the extent of pre-lithiation of the negative electrode active material, calculated by a specific equation, is 5 to 50%.