Si-LiF Composite Negative Electrode Active Material for Lithium-Ion Batteries
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Solution Overview
Problem
Conventional silicon-based negative electrode materials for lithium-ion batteries suffer from rapid volumetric swelling, instability, and poor conductivity, leading to degraded cycle characteristics and irreversible phenomena, limiting their commercialization potential.
Innovation Solution
The development of composite particles comprising silicon (Si) and lithium fluoride (LiF) mixed with a carbon phase, where Si—LiF mixed particles are dispersed within a carbon phase, with Si particles having a crystallite size of 20 nm or less and a carbon content of 10-90 wt%, enhancing conductivity and stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If silicon is used as a negative electrode material to achieve high capacity, then discharge capacity is improved, but volumetric swelling occurs during charging/discharging
Solution Approach 1:
Silicon particles are encapsulated within porous graphite particles, creating a nested structure where the inner silicon can swell and shrink without causing external structural failure. The porous graphite shell acts as a buffer that accommodates volume changes while maintaining overall particle integrity.
Solution Approach 2:
The graphite particles are designed with a porous structure that provides internal space for silicon expansion during lithiation. The porosity allows the silicon to swell without generating excessive stress that would lead to particle disintegration, while still maintaining electrical conductivity and ion transport pathways.
2Quantity of substance
If silicon particles are used to achieve high capacity, then discharge capacity is improved, but particle disintegration occurs due to swelling/shrinking
Solution Approach 1:
The nested structure of silicon inside porous graphite protects the silicon particles from mechanical disintegration during repeated swelling and shrinking cycles. The graphite shell maintains structural integrity while accommodating silicon volume changes, preventing particle fragmentation and maintaining electrode reliability over multiple cycles.
Solution Approach 2:
The invention creates a composite material system combining silicon and graphite with complementary properties. Graphite provides structural stability and flexibility, while silicon provides high capacity. The composite structure leverages the advantages of both materials to achieve high capacity with improved cycle stability.
3Stability of the object's composition
If alloy particles with Group 2A or transition metals are used to inhibit swelling, then volumetric stability is improved, but surface oxidation susceptibility increases
Solution Approach 1:
The invention uses a silicon-graphite composite that avoids the oxidation problem associated with alloying silicon with Group 2A or transition metals. Graphite is inherently more oxidation-resistant, and the composite structure provides both volumetric stability and reduced surface oxidation susceptibility compared to metal-alloyed silicon particles.
4Stability of the object's composition
If alloy particles with Group 2A or transition metals are used to inhibit swelling, then volumetric stability is improved, but electrical conductivity decreases
Solution Approach 1:
The silicon-graphite composite maintains good electrical conductivity through the graphite component, avoiding the conductivity loss associated with alloying silicon with Group 2A or transition metals. Graphite is inherently conductive, and the composite structure preserves electron transport pathways while providing volumetric 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 composite particles exhibit improved initial efficiency, reduced irreversible phenomena, and enhanced cycle life characteristics, leading to better battery performance and stability.
Implementation Method 1
lithium ions deintercalated from a positive electrode active material upon the first charging are intercalated into a negative electrode active material, such as carbon particles, and deintercalated again upon discharging
Implementation Method 2
a carbon phase containing a carbonaceous material... Si-LiF mixed particles are dispersed in the carbon phase
Implementation Method 3
forms an unstable solid electrolyte interphase (SEI) film to cause degradation of the performance of a battery
Data Source
AI summary
Composite particles and a negative electrode active material including such particles for an electrochemical device. The negative electrode active material is capable of lithium intercalation/deintercalation and includes composite particles including a carbon phase including a carbonaceous material, silicon (Si) and lithium fluoride (LiF). The Si and LiF may be present as Si—LiF mixed particles, which are dispersed in the carbon phase, wherein the Si—LiF mixed particles are dispersed in the carbon phase with uniform or non-uniform distribution. In addition, the composite particles include the carbon phase mixed uniformly or amorphously with the Si—LiF mixed particles.