Si-Metal Alloy Negative Electrode for High-Capacity Batteries
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Solution Overview
Problem
Current lithium-ion secondary batteries using graphite as negative electrode active material face limitations in capacity due to volumetric expansion during charging and discharging, leading to reduced battery life and capacity retention.
Innovation Solution
A negative electrode active material comprising a Si-metal alloy with controlled crystal grain size, specifically silicon alloyed with metals like Ti and Ni, is used to minimize volumetric expansion and maintain capacity retention during repeated charging and discharging cycles.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If graphite is used as negative electrode active material, then battery structure stability is maintained, but capacity is limited to 360 mAh/g
Solution Approach 1:
The invention changes the material parameter from graphite to Si-metal alloy, which has a higher theoretical capacity (4200 mAh/g for Si vs. 360 mAh/g for graphite). This parameter change enables the battery to achieve higher capacity while managing volumetric expansion through alloy formation and crystal grain control.
Solution Approach 2:
The invention uses composite Si-metal alloy materials combining silicon with other metals to create a material that exhibits both high capacity and reduced volumetric expansion. The composite structure allows Si to provide high capacity while the metal components help constrain volume changes during charging-discharging cycles.
2Quantity of substance
If Si is used to increase capacity, then battery capacity increases, but volumetric expansion occurs during charging and discharging
Solution Approach 1:
The invention changes the crystal grain size parameter of Si to nanoscale dimensions (average crystal grain size of 35 nm or less). This parameter change reduces volumetric expansion during lithium insertion/extraction cycles while maintaining high capacity, as smaller grains experience less cumulative volume change.
Solution Approach 2:
The invention applies local quality control by specifically targeting the crystal grain size of Si particles. By controlling the local structure (crystal grain dimensions) rather than changing the bulk material composition, the invention achieves reduced volumetric expansion while preserving the high capacity characteristics of Si.
3Reliability
If crystal grain size of Si is reduced, then capacity retention improves, but manufacturing precision requirements increase
Solution Approach 1:
The invention establishes a specific parameter range for crystal grain size (average size of 35 nm or less) that balances capacity retention improvement with manufacturing feasibility. This parameter specification provides a clear target for manufacturing processes while ensuring sufficient capacity retention after repeated charging-discharging cycles.
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 Si-metal alloy maintains high capacity retention and improves battery life by controlling the crystal grain size of crystalline silicon, preventing network frame breakage and maintaining electrochemical participation of particles.
Implementation Method 1
a negative electrode active material comprising a Si-metal alloy, which can provide a high-capacity battery, and a secondary battery which can retain a high capacity due to little volumetric expansion during charging and discharging
Implementation Method 2
In the Si-metal alloy according to the present invention, a crystal grain size of crystalline Si included in the Si-metal alloy can be controlled by simply adjusting an amount of Si contained in the Si-metal alloy, and a life characteristic of the secondary battery can be greatly improved by controlling the crystal grain size.
Data Source
AI summary
Provided are a negative electrode active material and a secondary battery including the same, more particularly relates to a negative electrode active material including a Si-metal alloy, which can provide a high-capacity battery, and a secondary battery which can retain a high capacity due to little volumetric expansion during charging and discharging, thereby demonstrating an excellent life characteristic of the secondary battery. The negative electrode active material includes a Si-metal alloy comprising a crystalline Si having a crystal grain size of 35 nm or less.