Silicon-Tin Alloy Negative Electrode Amorphization for Cycle Durability
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Solution Overview
Problem
Lithium ion secondary batteries using silicon-containing alloys face challenges in achieving sufficient cycle durability due to insufficient amorphization and lack of diffraction line peak shift, leading to reduced capacity and energy density suitable for vehicle applications.
Innovation Solution
A negative electrode active material with a silicon-containing alloy composition of Si x Sn y M z A a, where A represents unavoidable impurities, M is one or more transition metal elements, and the alloy is processed to extend the distance between Si regular tetrahedrons to 0.48 nm or more through Fourier transform processing and alloying treatments, enhancing amorphization and cycle durability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If a silicon-containing alloy is used as negative electrode active material, then capacity and energy density are improved, but cycle durability is insufficient due to volume expansion and contraction
Solution Approach 1:
The patent applies parameter changes by controlling the amorphous state of silicon through specific processing conditions (cooling rate of 10^5 to 10^8 K/s, adding specific elements like Al, Si, or C at controlled ratios). This changes the physical state and structure of silicon from crystalline to amorphous, which suppresses volume expansion during Li-ion insertion/extraction, thereby improving cycle durability while maintaining high capacity
Solution Approach 2:
The patent uses composite materials by creating an amorphous silicon-based alloy composite containing Si, Al, and at least one of Si, C, or B. This composite structure combines the high capacity of silicon with the structural stability provided by the amorphous phase and alloying elements, resolving the contradiction between high capacity and cycle durability
2Reliability
If amorphization of silicon is enhanced to improve cycle durability, then capacity retention is improved, but manufacturing precision and control become more difficult
Solution Approach 1:
The patent simplifies amorphization control by changing the processing parameter from complex thermal history control to a specific cooling rate range (10^5 to 10^8 K/s) during solidification. This parameter change makes amorphization achievable through conventional rapid cooling methods without requiring precise control of multiple thermal parameters, thereby improving manufacturing feasibility
Solution Approach 2:
The patent applies self-service by utilizing the natural rapid cooling that occurs during conventional solidification processes to achieve amorphization. The system itself provides the necessary rapid cooling condition through the solidification process, eliminating the need for external complex cooling apparatus or precise temperature control systems
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 cycle durability and capacity retention of lithium ion secondary batteries, enabling them to meet the high-energy density and output requirements for vehicle applications.
Implementation Method 1
a battery using a material to be alloyed with Li in the negative electrode is expected as a negative electrode material in a vehicle application since the energy density is improved
Implementation Method 2
the volume expansion in the case of occluding a Li ion is about 1.2 times for a graphite material, but a great volume change (about 4 times) occurs for the Si material since the amorphous state is converted to a crystalline state when Si and Li are alloyed
Data Source
Figure 1
Figure 2(A)~2(C)
Figure 3
AI summary
To provide a means capable of improving the cycle durability of an electric device such as a lithium ion secondary battery. A negative electrode active material which includes a silicon-containing alloy having a composition represented by Chemical Formula (I) : SixSnyMzAa (where, A is unavoidable impurities, M is one or two or more transition metal elements, x, y, z, and a represent values of percent by mass, and 0 < x < 100, 0 < y < 100, 0 < z < 100, and 0 ≤ a < 0.5 and x + y + z + a = 100) and in which a lattice image of the silicon-containing alloy obtained by using a transmission electron microscope is subjected to Fourier transform processing to obtain a diffraction pattern and a distance between Si regular tetrahedrons is 0.39 nm or more when the distance between Si regular tetrahedrons in an amorphous region is calculated from a Fourier image obtained by subjecting a diffraction ring portion present in a width of from 0.7 to 1. 0 when a distance between Si regular tetrahedrons is 1.0 in this diffraction pattern to inverse Fourier transform is 10 nm or less is used in an electric device.