Silicon-Oxygen Intermediate Layer for Lithium-Ion Battery Negative Electrodes
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Solution Overview
Problem
Lithium ion secondary batteries using silicon as a negative electrode face challenges with copper diffusion into the silicon thin film, leading to reduced charge/discharge cycle life and energy density due to the brittleness of the copper foil and excessive copper alloying, which existing methods struggle to control effectively.
Innovation Solution
A negative electrode design featuring a current collector with an intermediate layer composed of silicon and oxygen, which prevents copper diffusion into the active material layer through strong covalent bonding, allowing for higher temperature processing and increased production efficiency while maintaining adhesion and energy density.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If copper foil is used as current collector and silicon thin film is formed by vapor deposition or sputtering, then the silicon thin film is firmly bonded to the copper foil due to copper diffusion, but the copper foil becomes brittle and charge/discharge capacity is reduced due to excessive copper diffusion
Solution Approach 1:
An intermediate layer comprising silicon and oxygen (such as silicon oxide or silicon suboxide) is formed between the copper foil and the silicon active material layer. This intermediate layer acts as a diffusion barrier that prevents excessive copper diffusion into the silicon layer, thereby maintaining charge/discharge capacity while still ensuring adequate adhesion. The intermediate layer serves as a mediator that balances the conflicting requirements of strong bonding and diffusion prevention.
Solution Approach 2:
The negative electrode is constructed as a composite structure with multiple layers: copper foil current collector, intermediate layer (silicon-oxygen compound), and silicon active material layer. This composite structure combines the advantages of copper foil (high conductivity) with the protective function of the silicon-oxygen intermediate layer (diffusion barrier), achieving both strong adhesion and maintained capacity.
2Reliability
If the temperature of the current collector is controlled at less than 300°C during silicon thin film formation, then copper diffusion is suppressed, but production efficiency is reduced due to low deposition speed
Solution Approach 1:
The silicon-oxygen intermediate layer serves as a thermal and diffusion buffer that allows the deposition process to proceed at higher temperatures and speeds without causing excessive copper diffusion. The intermediate layer's stable silicon-oxygen bonds provide a barrier that protects against copper diffusion even when the current collector temperature is elevated for efficient production.
3Shape
If heat treatment is performed to relieve internal stress in the silicon thin film, then the copper foil curvature is reduced, but excessive copper diffusion occurs due to the heat treatment
Solution Approach 1:
The silicon-oxygen intermediate layer acts as a thermal barrier during heat treatment, preventing excessive copper diffusion even when the current collector is heated to relieve internal stress. This allows the heat treatment process to be performed effectively to improve flatness and reduce curvature without sacrificing charge/discharge capacity.
4Reliability
If an intermediate layer made of Mo or W is formed on the current collector surface, then copper diffusion is prevented, but the energy density decreases because these materials do not serve as active materials
Solution Approach 1:
The intermediate layer composition is changed from pure metal (Mo or W) to a silicon-oxygen compound system. This parameter change allows the intermediate layer to maintain its diffusion barrier function while the overlying silicon active material layer contributes to the energy density. The silicon in the intermediate layer can also participate in lithium alloying reactions, further contributing to capacity.
Solution Approach 2:
Instead of using a single non-active metal layer, the patent employs a composite structure where the silicon-oxygen intermediate layer is combined with the silicon active material layer. This composite approach ensures both diffusion prevention and maintains high energy density through the lithium-alloying capability of silicon.
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 intermediate layer effectively suppresses copper diffusion, maintaining the adhesion of the active material to the current collector, enhancing cycle characteristics and energy density, and allowing for higher production efficiency and lower costs.
Implementation Method 1
an intermediate layer which comprises silicon and oxygen and prevents the metal capable of being alloyed with silicon from diffusing into the active material layer
Implementation Method 2
intermediate layer composed of silicon and oxygen, which prevents copper diffusion into the active material layer through strong covalent bonding
Implementation Method 3
when such a material absorbs lithium, its crystal structure changes, so that its volume increases
Implementation Method 4
A large volume change in an active material on charge/discharge results in, for example, a poor contact between the active material and a current collector
Implementation Method 5
forming an amorphous silicon thin film on copper foil by vapor deposition or sputtering
Implementation Method 6
forming an amorphous silicon thin film on copper foil by vapor deposition or sputtering
Data Source
AI summary
A negative electrode for a lithium ion secondary battery includes a current collector, an intermediate layer formed on a surface of the current collector, and an active material layer formed on the intermediate layer. The current collector includes a metal capable of being alloyed with silicon. The active material layer includes an active material including silicon. The intermediate layer includes silicon and oxygen. The intermediate layer prevents the metal capable of being alloyed with silicon from diffusing into the active material layer. The diffusion of the constituent element of the current collector into the active material layer is suppressed.