Silicon-Titanium Anode Alloys With Nanograins for Longer Cycle Life
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Solution Overview
Problem
Existing silicon-based anode materials for lithium-ion batteries face challenges with high volume expansion during lithiation and electrolyte reactivity, leading to poor electrochemical cell life, and known methods of incorporating titanium nitride result in undesirable grain sizes and high costs.
Innovation Solution
Development of silicon-titanium-nitrogen alloys with controlled grain sizes and unique microstructures, produced through ball milling in nitrogen-rich or mixed atmospheres, which reduce volume expansion and electrolyte reactivity, and include additional elements like carbon or transition metals for improved performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If silicon-based anode materials are used to increase capacity, then energy density is improved, but volume expansion during lithiation increases leading to poor cell life
Solution Approach 1:
The patent uses composite materials by combining silicon with titanium nitride and titanium oxynitride phases to create a composite anode material. The silicon provides high capacity while the titanium-based phases constrain volume expansion and improve structural stability, resolving the contradiction between energy density and cell life
Solution Approach 2:
The patent changes the grain size parameter of the titanium nitride and titanium oxynitride phases to between 2-10 nm, which optimizes both the capacity and structural stability. This parameter control allows silicon to expand and contract while maintaining overall structure integrity, improving both energy density and cell life
2Use of energy by moving object
If silicon-based anode materials are used to increase capacity, then energy density is improved, but electrolyte reactivity increases
Solution Approach 1:
The titanium nitride and titanium oxynitride phases act as intermediary layers between silicon and the electrolyte. These intermediaries reduce direct contact and reaction between silicon and electrolyte, decreasing harmful reactivity while preserving silicon's high capacity benefits
Solution Approach 2:
The composite structure with titanium-based phases creates a protective matrix around silicon particles, reducing electrolyte reactivity while maintaining high energy density through the silicon component
3Stability of the object's composition
If titanium nitride is incorporated to reduce volume expansion, then structural stability is improved, but grain size control becomes difficult and costs increase
Solution Approach 1:
The patent specifies precise grain size parameters (2-10 nm) for titanium nitride and titanium oxynitride phases, transforming the manufacturing challenge into a controlled parameter optimization. This enables reproducible structural stability through controlled grain size rather than uncontrolled incorporation
Solution Approach 2:
The composite approach with both titanium nitride and titanium oxynitride phases provides multiple mechanisms for structural stability, making the system more robust to manufacturing variations while maintaining ease of production through established ball-milling techniques
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 alloys exhibit enhanced electrochemical performance with improved structural stability and cycling performance, achieving high reversible capacities and reduced grain sizes suitable for lithium-ion batteries.
Implementation Method 1
The step of ball milling is carried out in an atmosphere comprising nitrogen, a mixture of nitrogen and oxygen, or air
Data Source
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AI summary
An electrochemically active material includes an alloy represented by general formula (I): SiaTibOcNdMe, (I) where a, b, c, d, and e represent atomic % values, a + b + c + d + e = 100, M includes carbon or a transition metal element other than titanium, a > 20, a + b + e ≥ c + d, c ≥ 0, d > 5, e ≥ 0, and a/b > 0.5. The alloy includes a transition metal silicide, titanium nitride, or titanium oxynitride phase, and the phase has a Scherrer grain size that is greater than 2 nm and less than 10 nm.