Silicon Anode Crystal Orientation for Reduced Cracking
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Solution Overview
Problem
Silicon-based negative electrode active materials for lithium secondary batteries experience significant volume expansion during charging and discharging, leading to disconnection of conductive paths and deterioration of battery characteristics, limiting their commercialization despite their high capacity potential.
Innovation Solution
A silicon-based active material is prepared using a chemical processing method to control the crystal grain direction distribution, specifically incorporating a higher proportion of the (220) crystal plane and adjusting the crystal grain size and specific surface area to facilitate uniform lithium intercalation and deintercalation, reducing stress and cracking.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If a silicon-based compound is used as a negative electrode active material to increase capacity, then the discharge capacity is improved (10-fold higher than graphite), but the volume rapidly expands during charging, disconnecting the conductive path and deteriorating battery characteristics
Solution Approach 1:
The silicon-based compound particles are divided into fine particles with a particle diameter of 10 μm or less, and preferably 1 μm or less. This segmentation reduces the volume expansion stress on individual particles and prevents conductive path disconnection while maintaining high discharge capacity.
Solution Approach 2:
The patent applies different surface treatments to the silicon-based compound particles. Specifically, a coating layer is formed on the particle surface, and surface oxidation is controlled to create a specific surface structure. This local modification reduces volume expansion and maintains conductive path connectivity without sacrificing the high capacity of the bulk silicon material.
2Reliability
If the particle diameter of the silicon-based compound is reduced to suppress volume expansion, then the conductive path connectivity is improved, but the manufacturing complexity increases
Solution Approach 1:
The patent replaces mechanical particle size reduction methods (such as ball milling) with a chemical synthesis approach. Silicon-based compound particles are produced directly in the desired fine size range through chemical vapor deposition or sol-gel processes, eliminating the need for subsequent mechanical grinding and classification steps.
Solution Approach 2:
The patent controls the particle diameter parameter within a specific range (10 μm or less, preferably 1 μm or less) and maintains the silicon content within a defined range (70-100 wt%). By optimizing these parameters during synthesis, the desired particle size and performance are achieved without complex post-processing.
3Stability of the object's composition
If the silicon-based compound is coated with a thin film to suppress volume expansion, then the volume stability is improved, but the discharge capacity decreases
Solution Approach 1:
Instead of coating the entire particle surface with a thick protective layer, the patent applies a thin coating layer (controlled thickness) and creates surface oxidation only in specific regions. This localized treatment provides volume stability while minimizing the impact on the active silicon material that contributes to discharge capacity.
Solution Approach 2:
The patent optimizes the coating layer thickness and silicon content parameters to achieve the right balance. The coating layer is kept thin enough to allow lithium ion diffusion while providing structural support, and the silicon content is maintained at 70-100 wt% to ensure high capacity. These parameter optimizations prevent significant capacity loss while achieving volume stability.
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 enhances the service life and stability of the negative electrode by allowing uniform lithium mobility and reducing particle cracking, thereby improving the performance and longevity of the battery.
Implementation Method 1
a silicon-based particle having high discharge capacity may be used... for intercalating and de-intercalating lithium ions from the positive electrode
Implementation Method 2
when a silicon-based active material is prepared by a chemical processing method, the crystal grain direction distribution of the silicon-based active material itself can be controlled, and that the intercalation and deintercalation of lithium ions can be uniformly performed by controlling the crystal grain direction
Data Source
AI summary
A negative electrode active material, a method for preparing the same, a negative electrode composition and a negative electrode including the same, and a lithium secondary battery including the negative electrode are provided. The negative electrode active material comprises a silicon-based active material comprising a (220) crystal plane and a (111) crystal plane, the silicon-based active material comprising Si and optionally SiOx (0<x<2), Si being comprised in an amount of 70 parts by weight or more based on 100 parts by weight of the silicon-based active material, and the silicon-based active material satisfying 45≤(X/Y)×100, where Y is a proportion of the (111) crystal plane in the silicon-based active material, and X is a proportion of the (220) crystal plane in the silicon-based active material.