SiOx Negative Electrode Structure for Capacity and Cycle Stability
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Solution Overview
Problem
Lithium ion secondary batteries using silicon materials face challenges in achieving cycle stability equivalent to those using carbon-based active materials, as silicon oxide undergoes disproportionation and degradation during charging and discharging, leading to reduced cycle performance.
Innovation Solution
A negative electrode active material comprising a silicon compound (SiOx) with a peak in the range of 539 to 541 eV in the XANES spectrum, featuring a decreased long-range order structure of silicon dioxide, allowing for increased Li occlusion sites and improved cycle performance, combined with a carbon material surface layer for enhanced conductivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If silicon material is used as negative electrode active material to improve battery capacity, then battery capacity increases, but cycle performance deteriorates due to material breakage and electrolyte decomposition
Solution Approach 1:
The patent uses a composite material consisting of silicon oxide particles coated with a carbon material layer. The silicon oxide core provides high capacity (4199 mAh/g theoretical capacity) while the carbon coating layer prevents material breakage during expansion/contraction cycles and reduces electrolyte decomposition, thereby maintaining cycle performance.
Solution Approach 2:
The carbon material forms a thin film coating on the silicon oxide particles. This flexible carbon shell accommodates the volume changes of silicon oxide during charging/discharging cycles, preventing particle breakage while allowing lithium ion transport, thus resolving the contradiction between capacity and cycle stability.
2Stability of the object's composition
If silicon oxide is used to reduce material breakage, then structural stability improves, but battery capacity decreases compared to pure silicon
Solution Approach 1:
The patent changes the chemical composition parameter from pure silicon to silicon oxide (SiOx where 0.5 ≤ x ≤ 1.6). This parameter change reduces the expansion/contraction stress during cycling, improving structural stability, while still maintaining high theoretical capacity (4199 mAh/g) sufficient for high-performance batteries.
3Reliability
If carbon coating is applied to silicon oxide particles to improve conductivity, then electrical conductivity increases, but manufacturing complexity increases
Solution Approach 1:
The patent utilizes a heat treatment process that induces phase transition and chemical reaction between silicon oxide and carbon materials at elevated temperatures (600-1000°C). This thermal processing simultaneously improves electrical conductivity through graphitization and forms a stable carbon coating, achieving both goals through a single manufacturing step rather than multiple separate processes.
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 proposed solution results in higher battery capacity and favorable cycle performance for lithium ion secondary batteries, preventing degradation and maintaining performance over multiple charge cycles.
Implementation Method 1
silicon oxide undergoes disproportionation to Si and Li by repeating charging and discharging
Implementation Method 2
having a peak in a range of 539 to 541 eV in a XANES spectrum obtained by XANES measurement of the negative electrode active material particle
Implementation Method 3
the silicon dioxide component is decreased in long-range order structure. That is, when Li is inserted into the Si—O bond, at least part of the Si—O bonds can be decreased to form a Li—Si bond(s) or an O—Li bond(s)
Data Source
AI summary
A negative electrode active material containing a negative electrode active material particle; the negative electrode active material particle including a silicon compound shown by SiOx (0.5≤x≤1.6), and having a peak in a range of 539 to 541 eV in a XANES spectrum obtained by XANES measurement of the negative electrode active material particle. This provides a negative electrode active material that is capable of increasing battery capacity and improving cycle performance when it is used as a negative electrode active material for a secondary battery.