Silicon Composite Anode Structure for Stable SEI Thickness
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Solution Overview
Problem
Lithium secondary batteries face challenges with the non-uniform formation of the solid electrolyte interphase (SEI) layer on silicon-based anode active material particles, leading to reduced lifespan and operational stability due to high-volume expansion ratios during charging and discharging.
Innovation Solution
An anode with a composite particle structure, including silicon-based active material particles coated with a carbon layer and a polyacrylic acid-based copolymer binder, where the SEI layer is formed with a relative standard deviation of 20% or less after 100 cycles, ensuring uniform thickness and improved adhesion, thereby reducing side reactions and enhancing lifespan and stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If silicon-based particles are used as anode active material to increase capacity, then the energy density is improved, but the SEI layer formation becomes non-uniform due to high-volume expansion ratio, deteriorating life-span properties
Solution Approach 1:
The patent applies local quality by creating a multi-layered coating structure on silicon particles with different functional zones: an inner carbon coating layer that provides structural stability and accommodates volume expansion, and an outer SEI layer that enables lithium ion insertion/extraction. This localized functional differentiation allows the anode to simultaneously achieve high capacity from silicon and long cycle life from the protective coating structure.
Solution Approach 2:
The patent employs composite materials by combining silicon-based active material particles with carbon-containing coating layers and SEI layers. The composite structure integrates the high capacity advantage of silicon with the structural stability of carbon and the electrochemical functionality of the SEI layer, resolving the contradiction between high energy density and reliable lifespan performance.
2Quantity of substance
If silicon-based particles with high-volume expansion ratio are used, then the capacity is increased, but the SEI layer becomes non-uniformly formed, reducing operational stability
Solution Approach 1:
The patent applies local quality by creating a multi-layered coating structure on silicon particles with different functional zones: an inner carbon coating layer that provides structural stability and accommodates volume expansion, and an outer SEI layer that enables lithium ion insertion/extraction. This localized functional differentiation allows the anode to simultaneously achieve high capacity from silicon and long cycle life from the protective coating structure.
Solution Approach 2:
The patent applies beforehand cushioning by forming a carbon-containing coating layer on silicon particles before battery assembly. This pre-formed coating acts as a cushion that accommodates the volume expansion of silicon during lithiation, preventing mechanical fracture and maintaining structural integrity throughout cycling, thereby ensuring operational stability.
3Reliability
If the SEI layer is non-uniformly formed on silicon-based particles, then the life-span properties deteriorate, but increasing the uniformity requires additional coating processes that increase manufacturing complexity
Solution Approach 1:
The patent applies preliminary action by incorporating the carbon-containing coating layer formation as an integral part of the silicon particle synthesis process, performed before battery assembly. This preliminary coating step ensures uniform SEI layer formation and extends battery lifespan without requiring separate, complex post-synthesis coating equipment or processes.
Solution Approach 2:
The patent applies self-service by designing a synthesis process where the carbon-containing coating layer forms automatically on silicon particles during controlled carbonization. The system uses its own carbon source and thermal processing to create the protective layer, eliminating the need for external coating equipment and simplifying manufacturing while ensuring uniform SEI layer formation.
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 solution results in improved capacity retention and extended lifespan of lithium secondary batteries by maintaining a uniform SEI layer thickness and reducing resistance, thus enhancing operational stability and preventing capacity degradation.
Implementation Method 1
a solid electrolyte interphase (SEI) layer formed on at least a portion of a surface of the silicon-based active material particle
Implementation Method 2
an anode binder
Data Source
Figure 1~2
Figure 3
AI summary
An anode (130) for a lithium secondary battery includes an anode current collector (125), and an anode active material layer formed on at least one surface of the anode current collector (125). The anode active material layer includes an anode active material and an anode binder. The anode active material includes a plurality of composite particles, each of which includes a silicon-based active material particle, and a solid electrolyte interphase (SEI) layer formed on at least a portion of a surface of the silicon-based active material particle. A relative standard deviation of thickness values of the SEI layer which are measured by an X-ray photoelectron spectroscopy (XPS) from 9 different composite particles among the plurality of composite particles after repeating 100 cycles of charging and discharging is 20% or less.