Silicon Oxide Anode Network for Higher Initial Charge Efficiency
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Solution Overview
Problem
Lithium secondary batteries using silicon oxide as a negative electrode material face issues with irreversible reactions, low initial charge efficiency, and electrical short-circuits due to volumetric swelling and shrinking, which limit their cycle life and capacity.
Innovation Solution
A negative electrode comprising Mg-containing silicon oxide, graphene, and single-walled carbon nanotubes, where the graphene and nanotubes form an electrical network to prevent short-circuits and improve connectivity, with a D/G band intensity ratio of 0.8-1.5, and a binder to stabilize the structure, reducing the formation of lithium oxide and enhancing initial efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Duration of action of stationary object
If silicon oxide is used as 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 irreversible reactions producing lithium oxide
Solution Approach 1:
The patent extracts and removes lithium oxide, the harmful byproduct causing irreversibility, from the reaction system. By using silicon oxide with controlled composition (0.5 < x < 1.5) and conducting electrochemical reactions in a controlled environment, the formation of lithium oxide is minimized or prevented, thereby improving initial charge efficiency while maintaining cycle life characteristics.
Solution Approach 2:
The patent changes the compositional parameter of silicon oxide by controlling the value of x in SiOx (0.5 < x < 1.5). This parameter change optimizes the balance between capacity and irreversible reaction. Additionally, the patent controls the crystallite size parameter (3-10 nm) to further optimize electrochemical performance and reduce irreversible capacity loss.
2Duration of action of stationary object
If crystallite size of crystalline silicon is reduced to improve cycle characteristics, then cycle characteristics are improved, but limitation in reducing crystallite size prevents sufficient solution of micronization problem
Solution Approach 1:
The patent changes the material composition from pure crystalline silicon to silicon oxide (SiOx with 0.5 < x < 1.5), which allows for effective crystallite size reduction to 3-10 nm. This compositional change enables sufficient micronization that was not achievable with crystalline silicon alone, thereby fully resolving the micronization problem while improving cycle characteristics.
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 capacity efficiency of lithium secondary batteries by maintaining electrical connectivity during charge/discharge cycles and minimizing irreversible reactions, leading to enhanced cycle life and capacity retention.
Implementation Method 1
silicon oxide undergoes volumetric swelling during charge and volumetric shrinking during discharge
Implementation Method 2
graphene and single-walled carbon nanotubes form an electrical network to prevent short-circuits and improve connectivity
Implementation Method 3
silicon oxide undergoes reaction with lithium upon the initial charge to produce lithium silicide and lithium oxide
Data Source
AI summary
A negative electrode and a lithium secondary battery including the negative electrode. 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 plurality of Mg-containing silicon oxide, 2) a conductive material including a plurality of graphene and single-walled carbon nanotubes, and 3) a binder. The single-walled carbon nanotubes interconnect the Mg-containing silicon oxide through a linear contact, and the single-walled carbon nanotubes are interconnected by the graphene. The graphene has a D/G band intensity ratio of 0.8 to 1.5, and is an average value of the ratio of the maximum peak intensity of D band at 1360 ± 50 cm-1 to the maximum peak intensity of G band at 1580 ± 50 cm-1, as determined by Raman spectroscopy of graphene.