Nano Silicon Negative Electrode with Carbon and Polymer Layers
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Solution Overview
Problem
Lithium ion secondary batteries using silicon as the negative electrode active material face challenges due to large volume changes during charging and discharging, leading to short cycle life and low initial capacity, and existing methods for producing nano silicon materials result in low dispersibility and high energy consumption.
Innovation Solution
A negative electrode active material is developed comprising nano silicon aggregated particles with a plate-like structure and a carbon layer, where the nano silicon is produced by heating a layered polysilane in a non-oxidizing atmosphere, and a cationic polymer layer is added to improve stability and cycle characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If silicon is used as the negative electrode active material to achieve higher capacity, then the battery capacity increases, but the volume change during charging and discharging causes the silicon to turn into fine powder and detach from the current collector, shortening the cycle life
Solution Approach 1:
The patent embeds nano silicon particles within a porous carbon matrix structure, creating a nested configuration where the silicon is contained within the carbon framework. This nesting approach allows the silicon to expand and contract during lithium insertion/extraction without detaching from the current collector, thereby maintaining both high capacity and long cycle life.
Solution Approach 2:
The patent creates a composite material consisting of silicon particles combined with carbon matrix and conductive polymer. This composite structure combines the high capacity advantage of silicon with the structural stability and conductivity of carbon and polymer, resolving the contradiction between achieving high capacity and maintaining reliability over multiple cycles.
2Reliability
If silicon oxide (SiOx) is used as the negative electrode active material to suppress volume change, then the cycle characteristics improve, but the initial capacity is reduced due to the formation of a thick solid electrolyte interface (SEI) layer
Solution Approach 1:
The patent uses nano silicon instead of bulk silicon, creating a local quality change at the nanoscale. The nano silicon particles have smaller size and higher surface area to volume ratio, which allows for better lithium ion insertion/extraction kinetics and reduced SEI layer thickness, thereby improving initial capacity while maintaining the volume change suppression benefit of silicon oxide structures.
Solution Approach 2:
The patent changes the particle size parameter of silicon from micrometer scale to nanometer scale (1-5 nm as mentioned in the background). This parameter change fundamentally alters the electrochemical behavior, reducing the thickness of the SEI layer and improving lithium ion diffusion, thus increasing initial capacity while maintaining good cycle characteristics.
3Quantity of substance
If existing methods are used to produce nano silicon materials, then nano silicon can be obtained, but the dispersibility is low and energy consumption is high
Solution Approach 1:
The patent uses carbon matrix and conductive polymer as intermediary materials that facilitate the dispersion of nano silicon particles. These intermediary materials prevent aggregation of nano silicon particles and improve their dispersibility in the electrode slurry, while also providing a conductive network that enhances overall electrode performance without requiring high energy input during manufacturing.
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 new negative electrode active material enhances the cycle characteristics and initial capacity of lithium ion secondary batteries by mitigating volume changes and improving the dispersibility and stability of nano silicon, while reducing energy consumption in production.
Implementation Method 1
the nano silicon is produced by heating a layered polysilane in a non-oxidizing atmosphere
Implementation Method 2
a carbon layer having a thickness within a range of 1 nm to 100 nm and at least formed on a surface of the plate-like silicon body
Implementation Method 3
a cationic polymer layer including a cationic polymer covering the carbon layer
Implementation Method 4
silicon undergoes a large volume change associated with occlusion and release of Li during charging and discharging
Data Source
AI summary
Cycle characteristics of a nonaqueous secondary battery are to be improved.An active material including: a first active material that contains a nano silicon produced by heating a layered polysilane represented by a composition formula (SiH)n and having a structure in which multiple six-membered rings formed from silicon atoms are connected; and a second active material that contains a graphite, is used in a negative electrode. With this, expansion and contraction due to stress during charging and discharging can be mitigated, and thereby cycle characteristics improve.