Mg-Silicon Oxide Anode Coating to Limit Swelling Short-Circuits
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Solution Overview
Problem
Lithium secondary batteries using silicon oxide as a negative electrode material face challenges with irreversible reactions, low initial charge efficiency, and electrical short-circuits due to volumetric swelling and shrinking, which affect their capacity and life characteristics.
Innovation Solution
A negative electrode with a Mg-containing silicon oxide coated with a graphene layer and single-walled carbon nanotubes (SWCNTs) is developed, where the graphene coating layer has a specific D/G band intensity ratio, providing flexibility and preventing direct exposure to the electrolyte during swelling and shrinking, thus enhancing the battery's life characteristics and initial efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Duration of action of stationary object
If silicon oxide is used as a negative electrode active material, then cycle life characteristics are improved due to small volumetric change during charge/discharge, but initial charge efficiency deteriorates to 70-75% due to irreversible reactions producing lithium oxide and lithium silicate
Solution Approach 1:
A graphene coating layer is introduced as an intermediary between the silicon oxide active material and the electrolyte. This graphene layer prevents direct contact between lithium oxide/silicate byproducts and the electrolyte, thereby preventing harmful side reactions while allowing lithium ion transport. This resolves the contradiction by maintaining the cycle life benefits of silicon oxide while reducing irreversible capacity loss.
Solution Approach 2:
The graphene coating layer acts as a flexible thin film that accommodates the volumetric changes of silicon oxide during charge/discharge cycles. This flexible shell structure maintains structural integrity and prevents cracking, thereby preserving both the cycle life characteristics and initial charge efficiency of the silicon oxide-based negative electrode.
2Quantity of substance
If silicon is used as a negative electrode active material to achieve high theoretical capacity of about 4200 mAh/g, then capacity is improved to about 10 times that of graphite, but volumetric swelling during charge and shrinking during discharge causes micronization and isolation of particles, resulting in capacity degradation
Solution Approach 1:
The graphene coating layer acts as a flexible shell that accommodates the volumetric swelling and shrinking of silicon oxide during charge/discharge cycles. This prevents particle isolation and maintains conductive pathways, thereby preserving both the high capacity of silicon-based materials and the capacity retention required for reliable cycling performance.
Solution Approach 2:
The invention employs a composite material system combining silicon oxide with graphene coating and carbon nanotube integration. This composite structure maintains the high capacity characteristics of silicon-based materials while preventing micronization-related degradation through the flexible graphene shell and integrated conductive network.
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 significantly improves the life characteristics and initial efficiency of lithium secondary batteries by preventing electrical short-circuits and maintaining the graphene coating layer during volumetric changes, leading to higher capacity retention and reduced degradation.
Implementation Method 1
the graphene coating layer surrounding the surface of the Mg-containing silicon oxide... preventing direct exposure to the electrolyte during swelling and shrinking
Implementation Method 2
a conductive material including single-walled carbon nanotubes (SWCNTs)... functions to improve electroconductivity and to inhibit an electrical short-circuit
Implementation Method 3
silicon oxide... shows a small change in volume during charge/discharge structurally... undergoes volumetric swelling during charge and volumetric shrinking during discharge
Implementation Method 4
the graphene contained in the graphene coating layer has a D/G band intensity ratio... providing flexibility and preventing direct exposure
Data Source
AI summary
A negative electrode and lithium secondary battery including the same. The negative electrode includes: a current collector; and a negative electrode active material layer on at least one surface of the current collector. The negative electrode active material layer includes 1) a negative electrode active material including a Mg-containing silicon oxide particles, and a graphene coating layer surrounding the surface of the Mg-containing silicon oxide particles, 2) a conductive material including single-walled carbon nanotubes (SWCNT), and 3) a binder. The graphene contained in the graphene coating layer has a D/G band intensity ratio of 0.8 to 1.5, and the D/G band intensity ratio of the graphene is defined as an average value of the ratio of the maximum peak intensity of D band at 1360±50 cm−1 based on the maximum peak intensity of G band at 1580±50 cm−1, as determined by Raman spectroscopy of the graphene.