Silicon-Carbon Anode Composite Particles for Capacity and Cycle Stability
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Solution Overview
Problem
Lithium ion secondary batteries using silicon as a negative electrode active material face challenges due to volume expansion, leading to deterioration of cycle characteristics and insufficient discharge capacity, as composite particles with silicon and carbonaceous materials may not adequately address these issues.
Innovation Solution
The use of composite particles composed of amorphous carbonaceous and silicon particles, with specific silicon content and particle size ranges, along with controlled proportions and surface areas, to enhance the cycle characteristics and discharge capacity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If silicon particles are used as negative electrode active material to increase capacity, then discharge capacity is improved, but volume expansion occurs during charging leading to deterioration of cycle characteristics
Solution Approach 1:
Silicon particles are embedded within carbonaceous particles, forming a core-shell structure where the silicon core provides high capacity while the carbon shell constrains volume expansion. This nested configuration allows the inner silicon particles to expand during charging without damaging the overall composite structure, thereby maintaining cycle characteristics while achieving high discharge capacity.
Solution Approach 2:
The invention uses composite particles comprising both silicon particles and carbonaceous particles. The composite structure combines the high capacity advantage of silicon with the structural stability of carbonaceous materials, resolving the contradiction between achieving high discharge capacity and maintaining good cycle characteristics.
2Reliability
If composite particles with silicon and carbonaceous materials are used to improve cycle characteristics, then reliability is improved, but sufficient discharge capacity cannot be obtained
Solution Approach 1:
The composite particles exhibit local quality differentiation with silicon-rich cores providing high capacity and carbonaceous-rich shells providing structural stability. This local differentiation allows different regions of the same particle to fulfill different functions, achieving both high discharge capacity from the silicon core and good cycle characteristics from the carbonaceous shell.
Solution Approach 2:
By creating composite particles with specific silicon content ranges (0.5-5% for first composite particles, 60-70% for second composite particles) and controlling the volume proportion, the invention optimizes the balance between capacity and cycle stability, overcoming the limitation of insufficient discharge capacity in conventional composites.
3Ease of manufacture
If mechanochemical method is used to complex silicon and carbonaceous materials, then composite particles are formed, but silicon compound converts to silicon carbide reducing capacity
Solution Approach 1:
The invention changes the manufacturing parameters by controlling silicon particle size (1-50 nm average primary particle diameter) and using specific carbonaceous materials with defined surface areas. These parameter changes prevent excessive conversion to silicon carbide during mechanochemical processing, maintaining most silicon in its reactive metallic state for high capacity while still achieving good composite formation.
Data Source
AI summary
There is provided a negative electrode material for a lithium ion secondary battery according to a first aspect includes composite particles in which amorphous carbonaceous particles and amorphous silicon particles are complexed. An average primary particle diameter of the silicon particles is 1 nm or more and 50 nm or less. The composite particles include a first composite particle having a silicon content of 0.5% by weight or more and 5% by weight or less, and a second composite particle having a silicon content of 60% by weight or more and 70% by weight or less.