Composite Negative Active Material Ball for Li-Ion Batteries
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Solution Overview
Problem
Lithium-ion batteries face limitations with graphite due to its low theoretical discharge capacity, and silicon, while offering higher capacity, suffers from volume expansion issues leading to material rupture and increased SEI layer formation, which reduces coulombic efficiency and utilization rate.
Innovation Solution
A composite negative active material ball is developed, featuring a microscale electrically conductive metal core with silicon or silicon compound particles distributed on and embedded into its surface, maintaining contact during volume changes and reducing SEI layer formation through shared SEI films and prelithiation, enhancing electron transfer and lithium retention.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If silicon is used as negative active material to increase theoretical capacity, then discharge capacity is improved, but volume expansion causes material rupture and increased SEI layer formation
Solution Approach 1:
The patent embeds silicon particles inside a porous carbon shell, creating a nested structure where the silicon is contained within the carbon matrix. This nested configuration allows the silicon to expand and contract during lithium alloying/dealloying while the carbon shell provides structural support and prevents rupture, thus maintaining material stability while preserving high discharge capacity.
Solution Approach 2:
The carbon shell is designed with a porous structure that allows lithium ions to diffuse through while providing space for silicon volume expansion. The porosity accommodates the 300% volume change of silicon during charging and discharging, preventing material rupture and reducing harmful SEI layer formation by controlling electrolyte access.
2Reliability
If silicon is nanonized to minimize particle size and reduce expansion force, then material rupture is avoided, but surface area increases leading to larger SEI layer and higher lithium consumption
Solution Approach 1:
The patent applies different properties to different parts of the structure: the interior contains nanoscale silicon particles for crack resistance, while the exterior carbon shell provides a controlled surface that limits SEI layer formation. This local differentiation allows the interior silicon to be nanonized for mechanical stability while the exterior surface area is controlled to reduce lithium consumption.
Solution Approach 2:
The patent creates a composite structure combining nanoscale silicon particles with a porous carbon shell. The silicon provides high capacity and crack resistance through nanonization, while the carbon shell acts as a barrier that reduces the effective surface area exposed to electrolyte, thereby decreasing SEI layer formation and lithium consumption.
3Reliability
If microscale silicon spheres with nano-holes are used to absorb volume expansion, then structural stability is improved, but surface area remains large causing continued SEI layer regeneration
Solution Approach 1:
The patent uses a composite of silicon particles embedded in a porous carbon shell, where the carbon shell provides structural stability during volume expansion while simultaneously reducing the surface area exposed to electrolyte. This composite approach solves both the structural stability requirement and the electrolyte loss problem that plague microscale silicon spheres with nano-holes.
Solution Approach 2:
The patent extracts the silicon particles from direct contact with the electrolyte by embedding them within the carbon shell matrix. This extraction prevents the electrolyte from accessing the silicon surface directly, thereby reducing SEI layer regeneration and electrolyte loss while still allowing the silicon to undergo volume expansion within the protective carbon structure.
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 maintains good electron transfer characteristics, reduces irreversible lithium loss, and improves the dispersion and stability of silicon particles, leading to enhanced charge and discharge performance with reduced electrolyte consumption and increased coulombic efficiency.
Implementation Method 1
the silicon or silicon compound particles can maintain the direct contact of the electrically conductive metal core during the occurring of volume change of the silicon or silicon compound particles caused by the alloying with the lithium
Implementation Method 2
the electrically conductive metal core serves as the common internal electrically conductive element of the silicon or silicon compound particles
Implementation Method 3
the lithium can not be diffused through the contact points of the silicon particles any more
Data Source
AI summary
The invention discloses a composite negative active material ball, which includes an electrically conductive metal core, which is substantially without pores, and a plurality of silicon or silicon compound particles, which is distributed on the surface of electrically conductive metal core. Partial volume of the silicon or silicon compound particles are embedded into the electrically conductive metal core. The silicon or silicon compound particles can maintain the well contact of the electrically conductive metal core during alloying/dealloying with lithium. Therefore, the composite negative active material ball have good electrical transfer characteristics.