Microcrystalline Silicon Anodes With Carbon Shells Against Pulverization
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Solution Overview
Problem
Current lithium-ion batteries face challenges with the expansion and pulverization of silicon-based negative electrodes due to anisotropic stress, leading to rapid capacity fading and irreversible losses, particularly when using nanoscale silicon particles, which also pose risks of auto-ignition and SEI formation.
Innovation Solution
The development of nanoscaled amorphous silicon particles with a carbon coating, produced through vapor condensation and heat treatment, maintains an amorphous phase at higher temperatures, enabling improved cyclability and coulombic efficiency by reducing crystallite size and promoting isotropic expansion, thus stabilizing the electrode material.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If nanoscale silicon particles are used as active material, then specific capacity is improved, but particle stability deteriorates due to expansion and pulverization
Solution Approach 1:
The silicon particles are enclosed within a carbon coating shell, creating a core-shell structure where the silicon core provides high capacity while the carbon shell provides structural stability and prevents pulverization during lithiation/delithiation cycles
Solution Approach 2:
The invention uses composite silicon-carbon particles where nanoscale silicon provides the high lithium storage capacity while the carbon matrix provides mechanical strength and structural integrity, combining the advantages of both materials
2Speed
If silicon material is crystalline, then diffusion rate is improved, but stress resistance deteriorates due to anisotropic expansion
Solution Approach 1:
The invention changes the crystal structure parameter from crystalline to amorphous silicon, which transforms the expansion behavior from anisotropic to more isotropic, reducing internal stress and preventing pulverization while maintaining adequate diffusion rates
Solution Approach 2:
The carbon coating is applied selectively on the surface of silicon particles, providing localized stress relief and protection at the particle surface where expansion stresses are most severe, while leaving the bulk silicon structure intact for high capacity
3Use of energy by moving object
If negative electrode uses materials with higher lithium storage capacity, then specific energy is improved, but safety deteriorates due to auto-ignition risk
Solution Approach 1:
The carbon coating acts as an intermediary barrier between the silicon particles and the electrolyte, preventing direct contact that could lead to exothermic reactions and auto-ignition, while still allowing lithium ion transport
Solution Approach 2:
The carbon coating creates an inert protective environment around the reactive silicon particles, isolating them from the electrolyte and preventing harmful chemical reactions that could lead to safety issues
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 approach results in secondary lithium-ion batteries with enhanced specific capacity, high cyclability, and reduced risk of surface cracking, leading to improved performance and cost-effectiveness in mass production.
Implementation Method 1
nanoscaled amorphous silicon particles with a carbon coating, produced through vapor condensation
Implementation Method 2
produced through vapor condensation and heat treatment
Implementation Method 3
maintains an amorphous phase at higher temperatures, enabling improved cyclability
Data Source
AI summary
The present invention concerns a method for manufacturing microcrystalline nanoscaled silicon particles, the particles made thereof, and a secondary electrochemical cell utilising the particles as the active material of the negative electrode of the secondary electrochemical cell, wherein the silicon particles comprises a chemical compound of formula: Si(1−x)Mx, where 0.005≤x≤0.20 and M is at least one substitution element chosen from; C, N, or a mixture thereof, and wherein the particles have been subject to a heat treatment of 800 to 900° C. and transformed into a microcrystalline phase having crystallite sizes in the range of 1 to 15 nm.