Mg-Silicon Oxide Anode Coating for Swelling-Stable Conductivity
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Solution Overview
Problem
Existing silicon-based negative electrode materials for lithium secondary batteries face challenges with irreversible reactions, high irreversible capacity, and poor cycle life due to volumetric swelling and shrinking, leading to electrical short-circuits and degradation.
Innovation Solution
A negative electrode active material comprising Mg-containing silicon oxide coated with a carbon layer and a graphene layer, combined with single-walled carbon nanotubes, enhances electrical conductivity and flexibility, preventing exposure to electrolytes during swelling and shrinking.
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 volume change during charge/discharge, but initial charge efficiency decreases to 70-75% due to high irreversible capacity from lithium oxide production
Solution Approach 1:
A carbon coating layer is introduced as an intermediary between the silicon oxide particles and the electrolyte. This carbon layer prevents direct contact between lithium oxide (produced during initial charge) and the electrolyte, thereby reducing irreversible reactions while maintaining the volume stability benefits of silicon oxide during cycling.
Solution Approach 2:
A flexible carbon coating layer is applied around silicon oxide particles. This thin film shell accommodates the volume changes of silicon oxide during charge/discharge cycles while preventing harmful interactions with the electrolyte, thus preserving both cycle life and improving initial efficiency.
2Reliability
If carbon nanotubes are used as a conductive material with silicon oxide, then electroconductivity is improved, but electrical short-circuit occurs after volumetric shrinking/swelling due to separation from silicon oxide surface
Solution Approach 1:
The carbon coating layer and carbon nanotube conductive material are merged into a unified conductive network. The carbon coating layer serves dual functions: maintaining electrical contact with silicon oxide particles during volume changes and providing a stable matrix for carbon nanotubes, preventing separation and short-circuits.
Solution Approach 2:
A composite structure is created where carbon-coated silicon oxide particles are combined with carbon nanotubes. The carbon coating layer acts as an interface that ensures stable electrical contact between the silicon oxide core and the nanotube network, maintaining conductivity through swelling/shrinking cycles.
3Quantity of substance
If silicon is used as a negative electrode active material, then capacity is increased to about 4200 mAh/g (10 times graphite), but volumetric swelling during charge causes micronization and loss of conductive paths
Solution Approach 1:
Silicon oxide particles are used instead of bulk silicon, segmenting the active material into smaller units that undergo controlled volume changes. The carbon coating layer further segments each particle, providing individual protection and maintaining conductive paths even when particles undergo volumetric changes during cycling.
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 improves the life characteristics and high-temperature storage performance of lithium secondary batteries by maintaining an electrical network and preventing direct exposure of silicon oxide to electrolytes, thus enhancing initial capacity and efficiency.
Implementation Method 1
a carbon coating layer surrounding the surface of the Mg-containing silicon oxide and a graphene coating layer surrounding the surface of the carbon coating layer
Implementation Method 2
the graphene contained in the graphene coating layer has a D/G band intensity ratio of 0.8-1.5
Implementation Method 3
a conductive material including single-walled carbon nanotubes (SWCNTs)
Implementation Method 4
silicon undergoes volumetric swelling during charge and volumetric shrinking during discharge
Data Source
Figure 1(a)~1(b)
Figure 2(a)~2(b)
AI summary
Disclosed is a negative electrode and a lithium secondary battery including the same. The negative electrode includes: a current collector; and a negative electrode active material layer disposed on at least one surface of the current collector, and including: 1) a negative electrode active material including a Mg-containing silicon oxide, a carbon coating layer surrounding the surface of the Mg-containing silicon oxide and a graphene coating layer surrounding the surface of the carbon coating layer, 2) a conductive material including single-walled carbon nanotubes (SWCNTs), and 3) a binder, wherein the graphene contained in the graphene coating layer has a D/G band intensity ratio of 0.8-1.5, 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 graphene.