Silicon-Tin Alloy Negative Electrode for Battery Cycle Durability
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Solution Overview
Problem
Lithium ion secondary batteries for vehicle applications face challenges in achieving high cycle durability due to the large volume expansion and contraction of silicon-based negative electrode materials, leading to reduced lifespan and capacity trade-offs.
Innovation Solution
A silicon-containing alloy with a ternary or quaternary system composition, featuring an amorphous or low-crystalline silicon phase dispersed in a silicide phase, is used as the negative electrode active material, which suppresses phase transition and maintains Si-Si bond integrity during charge and discharge, enhancing electron conductivity and stress relaxation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If silicon-based negative electrode material is used to improve energy density, then capacity increases, but volume expansion and contraction occur leading to reduced cycle durability
Solution Approach 1:
The patent employs a composite material structure consisting of silicon particles embedded in a carbon matrix. The carbon matrix provides structural stability and accommodates volume expansion, while silicon provides high capacity. This composite approach resolves the contradiction by combining the high capacity of silicon with the structural stability of carbon, enabling both high capacity and good cycle durability.
Solution Approach 2:
The patent utilizes a carbon coating layer as a flexible shell surrounding silicon particles. This carbon shell accommodates volume expansion and contraction during charge-discharge cycles, preventing particle aggregation and maintaining electrical contact. The flexible carbon shell allows the silicon core to expand and contract without compromising the overall electrode structure, thus improving cycle durability while maintaining high capacity.
2Quantity of substance
If silicon material is used to achieve high capacity, then energy density improves, but structural integrity deteriorates due to phase transition from amorphous to crystalline state
Solution Approach 1:
The patent controls the crystalline state of silicon by adjusting processing parameters such as heating temperature and time during sintering. By maintaining silicon in an amorphous or fine-crystalline state rather than allowing complete crystallization, the patent preserves structural integrity while still achieving high capacity. This parameter control prevents excessive phase transition that would lead to particle aggregation and structural degradation.
Solution Approach 2:
The carbon matrix serves as a stabilizing framework that maintains structural integrity even when silicon undergoes phase transitions. The carbon matrix prevents silicon particles from aggregating during crystallization, maintaining the dispersed particle structure necessary for high capacity while providing overall structural stability to the electrode.
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
This configuration improves the cycle durability and capacity of lithium ion secondary batteries by allowing reversible lithium intercalation and deintercalation while maintaining structural integrity and electron conductivity.
Implementation Method 1
allowing reversible lithium intercalation and deintercalation
Implementation Method 2
enhancing electron conductivity
Implementation Method 3
maintains structural integrity and electron conductivity
Data Source
Figure 1
Figure 2
Figure 3A~3B
AI summary
[Problem] To provide a means capable of improving the cycle durability of an electric device such as a lithium ion secondary battery. [Solution] A negative electrode active material containing a silicon-containing alloy having ternary alloy composition represented by Si-Sn-M (M is one or two or more transition metal elements) or quaternary alloy composition represented by Si-Sn-M-Al (M is one or two or more transition metal elements) and having a structure wherein an a-Si phase containing amorphous or low crystalline silicon containing tin in a silicon crystal structure in form of a solid solution is dispersed in a silicide phase containing a silicide of a transition metal as a main component is used in an electric device.