Crystalline Silicon Graphite Negative Electrode for Lithium Ion Batteries
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Solution Overview
Problem
Lithium-ion secondary batteries with amorphous silicon and lithium alloys experience non-uniform phase formation, leading to deviations in negative electrode potential and degraded charge-state correlation, while existing studies on silicon particle size and mixing conditions with graphite are insufficient, resulting in suboptimal cycle characteristics and energy density.
Innovation Solution
A negative electrode active material comprising graphite particles and crystalline silicon particles with a median diameter of 0.7 μm or less, and a weight ratio of crystalline silicon to graphite of 1 wt% to 25 wt%, enhancing crystallinity and reducing volume expansion during charge and discharge.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If amorphous silicon is used as negative electrode active material, then high capacity is achieved, but non-uniform phase formation occurs leading to potential deviations and degraded charge-state correlation
Solution Approach 1:
The patent changes the physical state parameter of silicon from amorphous to crystalline form. This parameter change fundamentally alters the alloying behavior with lithium, preventing non-uniform phase formation while maintaining high capacity. The crystalline structure provides a more ordered and predictable reaction pathway with lithium ions.
Solution Approach 2:
The patent utilizes the phase transition aspect by employing crystalline silicon that undergoes controlled phase changes during lithium alloying. The crystalline-to-amorphous transition during charging is more uniform and predictable compared to starting with amorphous silicon, maintaining structural integrity and potential stability throughout the charge-discharge cycles.
2Quantity of substance
If silicon particle size is not optimized, then high energy density is achieved, but cycle characteristics deteriorate due to insufficient studies on particle size and mixing conditions
Solution Approach 1:
The patent optimizes the particle size parameter of crystalline silicon to a median diameter of 0.7 μm or less. This specific parameter optimization balances the competing requirements: small enough particles maintain structural integrity during cycling, while still providing sufficient lithium alloying capacity for high energy density.
Solution Approach 2:
The patent creates a dynamic composite structure where crystalline silicon particles of optimized size are mixed with graphite particles. This dynamic combination allows the silicon to expand and contract during cycling while the graphite provides structural stability, maintaining both high energy density and excellent cycle characteristics.
3Stability of the object's composition
If crystalline silicon particles with median diameter of 0.7 μm or less are used, then uniform phase formation and improved cycle characteristics are achieved, but particle size control complexity increases
Solution Approach 1:
The patent establishes a clear parameter specification (median diameter ≤ 0.7 μm) for crystalline silicon particles. This well-defined parameter target simplifies the manufacturing process by providing a concrete specification that can be controlled through standard particle size reduction techniques, despite the inherent complexity of achieving uniform small particle sizes.
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 results in a lithium-ion secondary battery with improved energy density and cycle characteristics, including increased capacity retention and reduced deterioration due to uniform silicon dispersion on graphite.
Implementation Method 1
when amorphous silicon and lithium are alloyed as in Patent Document 1, the crystalline phase of the lithium-silicon alloy easily becomes a non-uniform phase
Implementation Method 2
carbon material particles capable of absorbing and desorbing lithium ions
Data Source
AI summary
A negative electrode active material constituting a lithium ion secondary battery having high energy density and excellent cycle characteristics, and a negative electrode and a lithium ion secondary battery comprising the same are provided. The present invention relates to a negative electrode active material comprising graphite particles and crystalline silicon particles, wherein a median diameter of the crystalline silicon particles is 0.7 μm or less, and a weight ratio of the crystalline silicon particles to the total weight of the graphite particles and the crystalline silicon particles is 1 wt % or more and 25 wt % or less.