Si-Sn Composite Anode Powder for Lithium-Ion Cycle Stability
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Solution Overview
Problem
Lithium ion batteries face challenges in maintaining capacity and cycle characteristics due to the large volume expansion and contraction of silicon (Si) particles during lithium ion occlusion and release, leading to cracking and peeling off from the current collector, which deteriorates both initial and cycle characteristics.
Innovation Solution
A negative electrode material powder containing Si, Sn, and specific elements X and Y, with a phase proportion formula (a[Si]-b[SiX]-c[SnY], where the Si phase, SiX compound phase, and SnY compound phase are present separately, and their average particle diameters are within specific ranges to form a buffer region against Si expansion, improving cycle characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If Si is used as negative electrode active material to increase capacity, then theoretical capacity increases from 372 mAh/g to 4198 mAh/g, but volume expansion and contraction causes particle cracking and peeling off from current collector
Solution Approach 1:
The Si-based alloy particles are segmented into multiple phases (Si phase, Si compound phase, and Sn compound phase) rather than using pure Si. This segmentation allows each phase to handle expansion/contraction differently, with the Si phase providing high capacity and the compound phases providing structural stability, thus resolving the contradiction between high capacity and cycle characteristics.
Solution Approach 2:
The invention uses a composite material structure combining Si phase with Si compound phase and Sn compound phase in specific proportions. This composite approach leverages the high capacity of Si while the compound phases (particularly SiO2, SiN4, and SnO2) provide structural framework that accommodates volume changes, preventing particle cracking and maintaining cycle characteristics.
2Reliability
If Si particles are miniaturized to reduce expansion amount, then volume expansion is reduced, but initial characteristics such as initial discharge capacity and initial Coulombic efficiency decrease
Solution Approach 1:
The invention optimizes the particle diameter parameters of different phases within specific ranges (0.1-50 μm for all phases, with Si phase being 0.1-20 μm). By controlling these size parameters and their ratios, the invention achieves a balance where the Si phase is small enough to reduce expansion stress but large enough to maintain sufficient capacity, while the compound phases provide structural support without overly reducing the active Si content.
3Reliability
If alloying elements are added to prevent Si expansion, then cycle characteristics improve, but initial characteristics deteriorate
Solution Approach 1:
The invention applies local quality by having different phases with different functions distributed within the same particle. The Si phase (with specific local composition and size) provides high capacity and initial efficiency, while the Si compound phase and Sn compound phase (with their own specific compositions) are distributed throughout to provide structural stability and control expansion. This local differentiation allows each phase to optimize its function without compromising the other.
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 reduces the expansion of the Si phase, prevents collapse of the electrode structure, and balances initial and cycle characteristics by maintaining the Si phase and SnY compound phase proportions within optimal ranges, enhancing the battery's overall performance.
Implementation Method 1
Si has a theoretical capacity of 4198 mAh/g. However, since Si causes occlusion of Li ions by an alloying reaction with Li, Si has large volume expansion and contraction along with occlusion and release of the Li ions.
Data Source
AI summary
The present invention relates to a negative electrode material powder for a lithium ion battery, the negative electrode material powder containing Si, Sn, element X (X=Fe, Ni, Cr, Zr, and Ti), and element Y (Y=Cu, Fe, Ni, Cr, Co, Mn, Zr, and Ti), and including a Si phase, a SiX compound phase, and a SnY compound phase which are independently present in a state of being separated from each other with a phase ratio represented by a[Si]-b[SiX]-c[SnY] (a+b+c=100, 10≤a≤95, 1≤b≤90, and 0.07≤c≤50), wherein average particle diameters mdSi, mdSiX, and mdSnY in the respective phases all fall within the range of 0.1-50 μm, and the proportions of mdSi/mdSiX and mdSi/mdSnY all fall within the range of 0.1-5.0.