Silicon-Graphite Anode Structure for Low-Expansion Li-Ion Batteries
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Solution Overview
Problem
Lithium ion secondary batteries with negative electrodes containing specific elemental bodies like silicon face challenges with excessive expansion during charging, leading to reduced capacity and potential breakdown due to repulsive forces against electronic components.
Innovation Solution
A negative electrode material comprising a mixture of flat graphite particles aggregated or bonded with non-parallel surfaces and silicon oxide particles, where the positional relationship between the particles is not fixed, allowing for movable particles to fill spaces and maintain conductivity, thereby suppressing expansion and enhancing cycle characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If a specific elemental body (silicon) is used in a negative electrode to increase battery capacity, then the theoretical capacity increases, but the volume expansion during charging causes breakage and disconnection of electroconductivity
Solution Approach 1:
Silicon oxide particles are embedded within aggregated graphite particles, creating a nested structure where the high-capacity silicon is protected by the graphite matrix. This prevents direct exposure of silicon to electrolyte and confines expansion within the graphite structure, maintaining electroconductivity while utilizing silicon's high capacity.
Solution Approach 2:
The negative electrode uses a composite material system combining graphite and silicon oxide particles. Graphite provides structural stability and conductive network, while silicon oxide contributes high capacity. The composite structure synergistically combines the advantages of both materials to achieve high capacity with maintained reliability.
2Quantity of substance
If a specific elemental body (silicon) is used in a negative electrode to increase battery capacity, then the theoretical capacity increases, but the expansion creates repulsive force toward electronic components
Solution Approach 1:
Silicon oxide particles are nested within graphite aggregates, confining the expansion force within the graphite structure. The graphite matrix acts as a containment structure that absorbs and distributes the expansion stress, preventing transmission of repulsive forces to external electronic components.
Solution Approach 2:
The expansion is localized within the graphite aggregates containing silicon oxide, rather than affecting the entire electrode uniformly. The graphite structure provides local cushioning and stress distribution, containing the expansion forces at the particle level and preventing macroscopic deformation that would affect external components.
3Volume of moving object
If silicon oxide particles are aggregated with graphite particles, then expansion is suppressed, but particle arrangement affects electroconductivity
Solution Approach 1:
The negative electrode is segmented into multiple aggregated graphite particles, each containing silicon oxide. This segmentation allows independent expansion of each aggregate, preventing uniform stress distribution that would cause macroscopic deformation. The segmented structure maintains flexibility and electroconductivity through the network of graphite particles.
Solution Approach 2:
The composite structure of graphite and silicon oxide particles creates a multi-phase material system where graphite provides conductive pathways and structural framework, while silicon oxide provides capacity. The composite nature allows simultaneous achievement of expansion suppression and conductivity maintenance through the synergistic interaction of different materials.
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 effectively suppresses negative electrode expansion during charging, improves cycle characteristics, and maintains electroconductivity, leading to a lithium ion secondary battery with increased capacity and stability.
Implementation Method 1
when a specific elemental body forms an alloy during charging, the volume thereof is greatly increased
Implementation Method 2
flat graphite particles aggregated or bonded with non-parallel surfaces
Data Source
Figure 1A~2
Figure 3~4
Figure 5~6
AI summary
A negative electrode material for a lithium ion secondary battery, which is a mixture of first particles, in which plural flat graphite particles are aggregated or bonded such that principal surfaces of the graphite particles are not parallel to each other, and second particles including silicon atoms, and a method of producing the negative electrode material; and a negative electrode material slurry, a negative electrode for a lithium ion secondary battery, and a lithium ion secondary battery using the negative electrode material.