SiOx Negative Electrode Silicon Grain Size Control
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Solution Overview
Problem
Lithium ion secondary batteries using silicon as a negative electrode material face challenges in achieving cycle stability equivalent to those using carbon-based active materials, leading to reduced battery capacity and cycle characteristics.
Innovation Solution
A negative electrode active material with silicon compounds represented by SiOx (0.5≤x≤1.6) is developed, where the average diameter of silicon grains is between 0.25 nm to 5 nm, and a carbon material is coated on the surface to enhance conductivity and prevent degradation, ensuring improved battery capacity and cycle characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If silicon is used as a main raw material of the negative electrode active material to improve battery capacity, then the theoretical capacity increases significantly (10 times larger than graphite), but the negative electrode active material expands and shrinks during charge and discharge, causing it to break and lowering cycle characteristics
Solution Approach 1:
The silicon-based active material is divided into fine particles with a median diameter of 1 μm to 15 μm, and further into granules composed of multiple particles. This segmentation reduces the expansion and contraction stress on individual particles during charge-discharge cycles, preventing breakage and maintaining cycle characteristics while preserving high capacity.
Solution Approach 2:
A core-shell structure is created where silicon-containing particles are embedded within a coating layer. The coating layer (containing carbon material, silicon oxide, or both) encapsulates the silicon particles, providing mechanical support during expansion/contraction and preventing particle breakage, thus improving cycle stability while maintaining high capacity.
Solution Approach 3:
The negative electrode active material is formulated as a composite consisting of silicon-containing particles (providing high capacity) combined with carbon materials (providing structural stability and conductivity) and/or silicon oxide (modulating expansion). This composite structure achieves both high battery capacity and good cycle characteristics.
2Quantity of substance
If the surface layer of negative electrode active material is broken during charge and discharge, then a new surface is generated increasing the reaction area, but the electrolytic solution decomposes on the new surface forming a coating film that consumes the electrolytic solution and lowers cycle characteristics
Solution Approach 1:
A stable coating layer is pre-formed on the silicon particles before battery operation. This coating layer (containing carbon material and/or silicon oxide) provides a stable surface for electrolyte decomposition initially, forming a protective solid electrolyte interface (SEI) layer that prevents further electrolyte consumption and maintains cycle characteristics while allowing adequate Li-ion transport.
Solution Approach 2:
The coating layer acts as an intermediary between the silicon particles and the electrolytic solution. It mediates the interaction by providing a stable interface that controls electrolyte decomposition, preventing direct contact between the electrolyte and fresh silicon surfaces that would otherwise cause excessive coating film formation and capacity loss.
3Reliability
If silicon and oxygen are contained in the negative electrode active material to improve cycle characteristics, then the stability increases, but the battery capacity may be reduced compared to pure silicon
Solution Approach 1:
Silicon oxide is selectively distributed in specific regions rather than uniformly throughout the active material. The core-shell structure allows silicon-rich cores (providing high capacity) to be combined with oxide-containing shells (providing stability), creating local quality variations that optimize both capacity and cycle characteristics simultaneously.
Solution Approach 2:
The oxygen content is precisely controlled within specific ranges (silicon oxide content 5-50 at%, or x=0.5-1.6 in SiOx) to achieve optimal performance. This parameter optimization ensures sufficient structural stability from oxygen while maintaining adequate silicon content for high capacity, resolving the trade-off between stability and capacity.
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 results in a lithium ion secondary battery with high capacity and good cycle characteristics, as the silicon oxide degradation and load resistance are minimized, and Li ion diffusion is enhanced, maintaining stable battery performance.
Implementation Method 1
the silicon oxide degradation and load resistance are minimized
Implementation Method 2
Li ion diffusion is enhanced
Data Source
AI summary
A negative electrode active material contains particles of negative electrode active material, wherein the particles of negative electrode active material contain a silicon compound represented by SiOx (0.5≤x≤1.6), and when the particles of negative electrode active material are measured by an atom probe method, and an Si 75% equivalent concentration surface obtained by the atom probe method is defined to be a boundary surface of a silicon grain, an average diameter of the silicon grains at a center portion of the particle in the particles of negative electrode active material is in the range of 0.25 nm to 5 nm. According to this constitution, when it is used as the negative electrode active material of a secondary battery, a negative electrode active material is capable of increasing battery capacity and improving cycle characteristics.