Silicon-Carbon Negative Electrode Composition Against Short Circuits
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Solution Overview
Problem
Lithium secondary batteries with silicon-based negative electrodes face challenges in maintaining capacity and lifespan due to volume expansion and contraction during charging and discharging, leading to electrical short circuits and reduced lifespan properties.
Innovation Solution
A negative electrode with a specific weight ratio of silicon-based to carbon-based active materials (12:88 to 28:72) and a D50 to D90 ratio of 2 to 5 for the carbon-based to silicon-based materials, ensuring continuous conductive network maintenance and preventing electrical short circuits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If a silicon-based active material is used in the negative electrode to achieve high capacity, then the capacity increases significantly, but the volume expansion and contraction during charging and discharging causes electrical short circuits and degrades lifespan properties
Solution Approach 1:
The patent uses a composite structure of silicon-based active material particles embedded in a carbon-based active material matrix. The carbon-based material serves as a buffer that accommodates the volume expansion and contraction of silicon during charging and discharging cycles, preventing electrical short circuits while maintaining high capacity. This composite approach combines the high capacity advantage of silicon with the structural stability of carbon.
Solution Approach 2:
The carbon-based active material forms a flexible matrix that surrounds and supports the silicon-based particles. This flexible carbon matrix can deform elastically during volume changes, accommodating silicon expansion without causing structural failure or electrical short circuits, thereby improving lifespan properties while preserving high capacity.
2Stability of the object's composition
If a binder is used in a large amount to suppress volume expansion and contraction, then the structural stability improves, but the resistance increases and high-capacity electrode implementation becomes difficult
Solution Approach 1:
The patent changes the fundamental approach from using chemical binders to physically embedding silicon particles in a carbon-based active material matrix. This parameter change eliminates the need for large amounts of binder material, maintaining low resistance while achieving structural stability through the carbon matrix that naturally accommodates volume changes.
Solution Approach 2:
The carbon-based active material serves as an intermediary between the silicon-based particles and the conductive network. It provides structural support and stability while maintaining electrical conductivity, replacing the traditional binder function without increasing resistance or sacrificing capacity.
Data Source
AI summary
The present invention relates to a negative electrode including a negative electrode current collector, and a negative electrode active material layer disposed on the negative electrode current collector, wherein the negative electrode active material layer includes a negative electrode active material containing a silicon-based active material and a carbon-based active material at a weight ratio of 12:88 to 28:72, and a ratio of D50 of the carbon-based active material to D90 of the silicon-based active material is 2 to 5.