Si-Based Negative Electrode Composition for Stable High-Rate Cycling
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Solution Overview
Problem
Silicon-based negative electrode active materials for lithium secondary batteries face challenges in maintaining cycle characteristics and reducing plateau regions in discharge profiles, leading to decreased battery performance and safety, especially when used in combination with carbon materials like graphite.
Innovation Solution
A Si-based negative electrode active material comprising silicon (Si) and a compound containing Si and a semimetal/metal element M, with a Si content of more than 50 wt%, oxygen content less than 30 wt%, and a semimetal/metal element content between 10 wt% and 50 wt%, characterized by specific X-ray diffraction patterns and true density, which improves cycle characteristics and eliminates plateau regions in discharge profiles.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If silicon-based active material is used to increase capacity, then capacity per mass increases 5 to 10 times compared to graphite, but electron conductivity decreases
Solution Approach 1:
The patent uses a composite structure where silicon particles are embedded in a carbon matrix. The carbon component provides electron conductivity while the silicon component provides high capacity. This composite approach allows the material to benefit from both high capacity and good conductivity simultaneously.
Solution Approach 2:
The carbon matrix acts as an intermediary that facilitates electron transport to and from the silicon particles. It mediates the electrical connection between silicon particles and the current collector, solving the conductivity problem without reducing the silicon content needed for high capacity.
2Quantity of substance
If silicon-based active material undergoes large volumetric changes during charge and discharge cycles, then capacity is maintained, but separation from conductive auxiliary agent occurs, leading to deterioration of cycles and reduction of energy density
Solution Approach 1:
The carbon matrix acts as a flexible shell that can accommodate the volumetric changes of silicon particles during lithiation and delithiation. This flexible carbon coating maintains structural integrity and prevents particle separation, solving the cycle stability problem while preserving capacity.
Solution Approach 2:
The patent merges the silicon particles with the carbon matrix into a unified composite structure. This merging ensures that the conductive auxiliary agent and active material remain integrated even during volumetric changes, preventing separation and maintaining cycle characteristics.
3Object-affected harmful factors
If average particle diameter of active material particles is increased to reduce specific surface area, then contact area with electrolyte is reduced and swelling is suppressed, but electron conductivity pathways are lengthened
Solution Approach 1:
The patent applies local quality by creating a carbon-rich environment around each silicon particle. This local carbon distribution ensures short electron conductivity pathways at the particle level, while the overall particle size can be optimized to reduce electrolyte contact and swelling.
Solution Approach 2:
The composite material is segmented into small silicon particles dispersed in the carbon matrix. This segmentation maintains short electron pathways within each composite unit while allowing the overall electrode structure to have reduced specific surface area, balancing conductivity and swelling suppression.
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 Si-based negative electrode active material enhances cycle characteristics, maintains discharge profiles at high rates, and can be used effectively alone or in combination with carbon materials, improving battery performance and safety.
Implementation Method 1
a Si-based negative electrode active material comprising Si and a compound containing Si and a semimetal/metal element M
Implementation Method 2
the silicon-based active material undergoes large volumetric changes caused by intercalation and deintercalation of lithium ions
Implementation Method 3
in an X-ray diffraction pattern as measured by a powder X-ray diffraction (XRD) device using Cu-Kα1 rays
Data Source
AI summary
A Si-based negative electrode active material that is capable of improving cycle characteristics, reducing or eliminating a plateau region in the discharge profile, and further improving high-rate characteristics. The Si-based negative electrode active material contains Si and a compound containing Si and a semimetal/metal element M, wherein the content of Si in the negative electrode active material is more than 50 wt %; the content of oxygen atoms (O) is less than 30 wt %; the content of the semimetal/metal element M is more than 10 wt % and less than 50 wt %, wherein in an X-ray diffraction pattern as measured by a powder X-ray diffraction (XRD) device using Cu-Kα1 rays, the full width at half maximum of the peak of the (111) plane of Si is 0.25° or more; and wherein the peak intensity of the peak of the (111) plane of Si is less than 20,000 cps; and the true density is 2.5 g/cm3 or more.