Si-Sn-Ti Alloy Negative Electrode for Li-Ion Batteries
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Solution Overview
Problem
Lithium ion secondary batteries face a decrease in cycle life due to the amorphous-crystal phase transition when silicon is alloyed with lithium, leading to a trade-off between capacity and cycle durability.
Innovation Solution
A negative electrode active material comprising a Si-Sn-Ti series alloy with specific composition ranges (46%≤Si≤58%, 7%≤Sn≤21%, 24%≤Ti≤37%) is used to suppress amorphous-crystal phase transition, enhancing cycle life and capacity retention.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If silicon is alloyed with lithium to increase capacity, then the capacity of the negative electrode is improved, but the cycle life decreases due to amorphous-crystal phase transition and volume change
Solution Approach 1:
The patent uses a composite material system consisting of Si-Sn-Ti alloy particles with specific composition ratios (Si: 46-58 mass%, Sn: 7-21 mass%, Ti: 24-37 mass%). This composite alloy structure leverages the complementary properties of each element: Si provides high capacity, while Sn and Ti suppress amorphous-crystal phase transition and reduce volume expansion, thereby simultaneously achieving high capacity and long cycle life
Solution Approach 2:
The patent optimizes the compositional parameters of the alloy by precisely controlling the mass percentages of Si, Sn, and Ti within specific ranges. This parameter optimization ensures the alloy maintains an amorphous structure during lithium alloying, preventing phase transition and volume expansion while maximizing lithium storage capacity
2Quantity of substance
If Si series active material is used to achieve high capacity, then the energy density is improved, but the cycle durability deteriorates due to trade-off relationship between capacity and stability
Solution Approach 1:
The Si-Sn-Ti composite alloy combines three elements with complementary functions: Si contributes to high energy density, while Sn and Ti work together to maintain structural stability during cycling. This composite approach breaks the traditional trade-off between capacity and durability by distributing different functions across multiple elements
Solution Approach 2:
The patent creates local structural differences within the alloy particles by dispersing microcrystalline or amorphous regions of different composition throughout the material. This local quality variation allows different regions to perform different functions: some regions maximize lithium storage while others maintain structural integrity
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-Sn-Ti series alloy ensures high capacity and cycle durability, with discharge capacity retention exceeding 90% after 50 cycles and 43% after 100 cycles, improving the overall performance of lithium ion secondary batteries.
Implementation Method 1
when silicon is alloyed with lithium and thereby resulting in a great change in volume
Implementation Method 2
a shift from an amorphous state to a crystalline state caused when silicon is alloyed with lithium
Data Source
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AI summary
A negative electrode active material for an electric device includes an alloy containing, in terms of mass ratio, 35%≤Si≤78%, 7%≤Sn≤30%, 0%<Ti≤37% and/or 35%≤Si≤52%, 30%≤Sn≤51%, 0%<Ti≤35%, and inevitable impurities as a residue. The negative electrode active material can be obtained with a multi DC magnetron sputtering apparatus by use of, for example, silicon, tin and titanium as targets. An electric device employing the negative electrode active material can keep a high discharge capacity and ensure a high cycle property.