Silicon Core-Shell Powder for Li-Ion Anode Cycle Life
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Solution Overview
Problem
Current silicon-based negative electrodes for Li-ion batteries face challenges with irreversible capacity losses and cycle life due to volume expansion and reactivity issues, limiting their performance compared to graphitic carbon anodes.
Innovation Solution
A silicon-based powder with a core-shell structure is developed, where the core contains silicon and the shell is composed of silicon oxide (SiOx) with a high percentage of Si4+ cations, optimized to reduce volume expansion and improve mechanical resistance, ionic conductivity, and stability, and the shell's thickness and composition are tailored to minimize reactivity and enhance interaction with binders.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If silicon-based materials are used to replace graphitic carbon in negative electrodes, then energy density is improved, but irreversible capacity loss and cycle life are worsened due to volume expansion and reactivity issues
Solution Approach 1:
The patent applies the nested doll principle by creating a core-shell structure where silicon particles (core) are enclosed within a protective silicon oxide shell. This nested configuration allows the high-capacity silicon material to be protected from degradation while maintaining its electrochemical activity, thereby improving cycle life without sacrificing energy density
Solution Approach 2:
The patent employs composite materials by combining silicon with silicon oxide to form a hybrid structure. The silicon core provides high capacity while the silicon oxide shell provides structural stability and protects against unwanted reactions, creating a composite material that balances high energy density with improved reliability and cycle life
2Quantity of substance
If silicon-based materials are used to replace graphitic carbon in negative electrodes, then energy density is improved, but mechanical integrity is worsened due to volume expansion during lithiation
Solution Approach 1:
The nested doll principle is applied by enclosing silicon particles within a protective silicon oxide shell. This nested structure constrains the silicon core during volume expansion, preventing mechanical degradation and maintaining electrode integrity while preserving the high capacity benefits of silicon
Solution Approach 2:
The patent utilizes a thin film approach by creating a silicon oxide shell of optimized thickness (0.5-10 nm) that provides mechanical constraint during volume expansion. This thin protective film accommodates the expansion stresses while maintaining structural integrity, preventing particle fragmentation and electrode degradation
3Strength
If the shell thickness is increased to improve stability, then mechanical resistance is improved, but ionic conductivity and electrical conductivity are worsened
Solution Approach 1:
The patent applies parameter changes by optimizing the shell thickness to a specific range (0.5-10 nm) that balances mechanical protection with ionic conductivity. This precise parameter control ensures the shell is thick enough to provide structural stability but thin enough to allow efficient lithium ion transport, resolving the contradiction between mechanical resistance and ionic conductivity
Solution Approach 2:
The patent implements local quality by creating a gradient in shell composition and thickness, with the silicon oxide shell having varying properties through its thickness. This local variation in material properties allows the outer regions to provide mechanical protection while inner regions maintain ionic conductivity, optimizing both functions simultaneously
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 powder results in Li-ion batteries with reduced irreversible capacity loss and improved cycle life, maintaining mechanical integrity and enabling optimal electrode preparation with enhanced storage life and performance.
Implementation Method 1
the shell has a thickness of at least 0.5 nm, more preferably at least 0.75 nm, most preferably at least 1.0 nm... the shell volume comprises SiOx with 0
Data Source
Figure 1
Figure 2.1~2.3
Figure 3
AI summary
The invention relates to a powder comprising particles containing a core and a shell, said powder preferably having a surface area (BET) of at most 50 m2/g, said core containing silicon (Si) and said shell containing silicon oxide SiOx with 0<x≤2, wherein said silicon oxide contains Sin+ cations with n being an integer from 1 to 4, wherein said silicon oxide contains Si4+ cations in an amount of at least 70 mol% from the total amount of Sin+ cations.