Negative Electrode Particle Layout to Prevent Silicon Isolation
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Solution Overview
Problem
The expansion and contraction of silicon-containing materials in negative electrodes of secondary batteries cause poor electrical contact and isolation issues, leading to inadequate cycle characteristics and discharge capacity.
Innovation Solution
A negative electrode active material comprising a first carbon material with specific particle diameter ratios to a second carbon material and a silicon-containing material, which are strategically positioned to maintain conductive paths and suppress expansion and contraction, enhancing discharge capacity and cycle characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If silicon-containing material is used as negative electrode active material, then discharge capacity is improved, but electrical contact and cycle characteristics deteriorate due to expansion and contraction
Solution Approach 1:
The patent applies nesting by placing silicon-containing material particles inside the internal voids of three-dimensional networked graphite particles. This nested structure allows the silicon to expand and contract within the confined space provided by the graphite matrix, preventing isolation while maintaining electrical contact. The graphite acts as a container that accommodates the volume changes of silicon during charge-discharge cycles.
Solution Approach 2:
The patent uses a composite material system combining graphite and silicon-containing material in specific weight ratios (graphite 90-99.9 wt%, silicon-containing material 0.1-10 wt%). This composite structure leverages the high capacity of silicon while using graphite to provide structural stability and maintain conductive pathways, resolving the contradiction between capacity improvement and cycle stability.
2Quantity of substance
If silicon-containing material expands considerably during charge, then discharge capacity increases, but conductive paths are broken and electrical contact is lost
Solution Approach 1:
By nesting silicon-containing material within the three-dimensional networked graphite structure, the patent ensures that silicon particles remain physically constrained within the graphite matrix. The graphite network provides a continuous conductive pathway that remains intact even when silicon expands, preventing isolation and maintaining electrical contact throughout charge-discharge cycles.
Solution Approach 2:
The three-dimensional networked graphite structure acts as a flexible matrix that can accommodate the expansion and contraction of silicon-containing material. The network structure deformable nature allows it to flex with volume changes while maintaining structural integrity and continuous conductive pathways, preventing silicon isolation.
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 proposed configuration significantly improves the electrical contact and maintains conductive paths, resulting in enhanced discharge capacity and improved cycle characteristics of the secondary battery.
Implementation Method 1
a negative electrode active material capable of electrochemically absorbing and releasing lithium ions
Implementation Method 2
The SiO x proposed by Patent Literature 1 expands considerably during charge and contracts during the subsequent discharge
Data Source
Figure 1~2
AI summary
A negative electrode for a secondary battery including a negative electrode active material capable of absorbing and releasing lithium ions. The negative electrode active material includes a first carbon material as a main component, and includes a second carbon material and a silicon-containing material which are present between particles of the first carbon material. The first carbon material has an average particle diameter A, the second carbon material has an average particle diameter B, and the silicon-containing material has an average particle diameter C, satisfying A > C ≥ B.