Si-Zn-M Alloy Negative Electrode for Battery Cycle Life
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Solution Overview
Problem
Lithium ion secondary batteries using carbon/graphite-based negative electrodes struggle to achieve high initial capacity and cycle durability due to limitations in charge/discharge capacity and energy density, while alloyed Si negative electrodes face issues with volume expansion and cycle lifetime.
Innovation Solution
A ternary Si—Zn-M-based alloy is used as the negative electrode active material, with elongation of the electrode layer set within a specific range (1.29<δ<1.70%) to suppress amorphous-crystalline phase transition and enhance cycle lifetime, allowing for high initial capacity and improved discharge capacity retention.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If alloyed Si material is used for negative electrode, then energy density is enhanced, but volume expansion occurs causing lowered cycle lifetime
Solution Approach 1:
The invention changes the physical state parameter of Si from crystalline to amorphous form. This parameter change suppresses the large volume expansion (approximately four times) that occurs in crystalline Si during lithium alloying, thereby improving cycle lifetime while maintaining high energy density
Solution Approach 2:
The invention creates a composite structure by mixing amorphous Si particles with graphite particles in specific proportions (Si: 30-70 wt%, graphite: 30-70 wt%). This composite material combines the high capacity of Si with the structural stability of graphite, resolving the contradiction between energy density and cycle lifetime
2Reliability
If carbon/graphite-based material is used for negative electrode, then cycle lifetime is improved, but charge/discharge capacity is limited to theoretical capacity of 372 mAh/g
Solution Approach 1:
The invention uses a composite material system combining amorphous Si and graphite. The amorphous Si provides high theoretical capacity (3200 mAh/g or higher) while graphite provides structural stability and long cycle life. The synergistic combination allows the negative electrode to achieve both high capacity and excellent cycle lifetime
3Quantity of substance
If Si material is used for negative electrode, then initial capacity is enhanced, but large volume change occurs during charge/discharge
Solution Approach 1:
The invention changes the crystalline structure parameter of Si from ordered crystalline to disordered amorphous state. This structural parameter change fundamentally alters the volume expansion behavior during lithium alloying, reducing volume change from approximately four times in crystalline Si to a much smaller extent in amorphous Si
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 ternary Si—Zn-M-based alloy achieves a balance of high initial capacity and cycle durability, effectively addressing the limitations of carbon/graphite and alloyed Si electrodes by optimizing the electrode's structural properties and reaction dynamics.
Implementation Method 1
a battery using a material, which is alloyed with Li, for the negative electrode
Implementation Method 2
charge/discharge is performed by occlusion/discharge of lithium ions into/from graphite crystals
Implementation Method 3
elongation of the electrode layer set within a specific range (1.29<δ<1.70%) to suppress amorphous-crystalline phase transition
Implementation Method 4
in an event where Si and Li are alloyed with each other, the Si material makes transition from an amorphous state to a crystal state and causes a large volume change (approximately four times)
Data Source
AI summary
A negative electrode for an electrical device includes: a current collector; and an electrode layer containing a negative electrode active material, an electrically-conductive auxiliary agent and a binder and formed on a surface of the current collector, wherein the negative electrode active material contains an alloy represented by a following formula (1): SixZnyMzAa (in the formula (1) M is at least one metal selected from the group consisting of V, Sn, Al, C and combinations thereof, A is inevitable impurity, and x, y, z and a represent mass percent values and satisfy 0<x<100, 0<y<100, 0<z<100, 0≤a<0.5 and x+y+z+a=100), and elongation (δ) of the electrode layer is 1.29<δ<1.70%.