Nano-Si Negative Electrode Composition for Longer Li-Ion Cycle Life
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Solution Overview
Problem
Lithium ion battery negative electrodes face challenges with silicon (Si) particles expanding due to lithium insertion, leading to peeling off during charge and discharge cycles, which reduces cycle characteristics and battery life, and using nano-sized Si increases binder requirements, affecting capacity and longevity.
Innovation Solution
A negative electrode with a mixture of nano-Si particles, an organic solvent-based binder, and hydrophobized cellulose, where hydrophilic groups of cellulose are substituted with hydrophobic groups to reduce volume expansion and improve binding, is used, along with a method of forming a slurry and applying it to a current collector.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If Si particles are used as negative electrode active material to increase capacity, then cell battery capacity increases, but volume expansion occurs due to lithium insertion causing peeling off and reduced cycle characteristics
Solution Approach 1:
The Si particles are divided into fine particles with a maximum diameter of 10 μm, and preferably an average diameter of 1 μm or less. This segmentation reduces the volume expansion stress during lithium insertion, preventing peeling off and improving cycle characteristics while maintaining high capacity.
Solution Approach 2:
The negative electrode mixture layer is formed as a composite material containing Si fine particles, a water-based binder, and a cellulose derivative. This composite structure provides both high capacity from Si and improved adhesion from the binder-cellulose complex, resolving the contradiction between capacity and cycle life.
2Reliability
If nano-Si is used to reduce volume expansion influence, then cycle characteristics improve, but surface area increases requiring larger amount of binder which decreases cell battery characteristics
Solution Approach 1:
The binder content is controlled within a specific range of 1-10 wt% based on the total weight of the negative electrode mixture layer. This parameter optimization ensures sufficient binding for nano-Si particles while preventing excessive binder from reducing cell battery characteristics, achieving both improved cycle life and maintained performance.
Solution Approach 2:
The cellulose derivative with degree of substitution 0.3-2.0 provides localized adhesion enhancement at the binder-Si interface. This local quality improvement allows effective binding with minimal binder content, preventing the trade-off between binding strength and cell battery characteristics.
3Strength
If water-based binder is used to bind nano-Si particles, then binding strength increases, but Si reacts with water generating hydrogen gas which decreases cell battery characteristics
Solution Approach 1:
A cellulose derivative acts as an intermediary substance between the water-based binder and Si particles. The cellulose derivative with controlled hydrophilicity (degree of substitution 0.3-2.0) provides binding functionality while reducing direct water-Si contact, thereby maintaining binding strength while minimizing hydrogen gas generation.
Solution Approach 2:
The degree of substitution of the cellulose derivative is controlled within 0.3-2.0 to optimize the balance between hydrophilicity and hydrophobicity. This parameter control allows the cellulose to maintain water-based binder compatibility for strong binding while reducing water reactivity with Si particles to prevent hydrogen gas generation.
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 enhances the capacity and cycle characteristics of lithium ion batteries by minimizing the negative effects of Si expansion and binder usage, resulting in improved battery life and performance.
Implementation Method 1
the hydrophobized cellulose results from substitution of a part of hydrophilic groups of cellulose by a hydrophobic group
Implementation Method 2
the binder is an organic solvent-based binder
Data Source
AI summary
a negative electrode for a lithium ion cell battery capable of increasing a cell battery capacity and improving cell battery characteristics such as cycle characteristics is provided. A negative electrode mixture layer 1M including a negative electrode active material, a binder, and hydrophobized cellulose is formed as described below. The negative electrode active material includes nano-Si, the binder is an organic solvent-based binder (polyimide or polyvinylidene fluoride), and the hydrophobized cellulose results from substitution of a part of hydrophilic groups of cellulose by a hydrophobic group. When the organic solvent-based binder is used as described above, reaction between water and Si can be prevented, and the electrode characteristics can be improved. In a general technique, the addition amount of the organic solvent-based binder needs to be increased because of use of the Nano-Si, and therefore, this decreases the cell battery capacity and the cycle characteristics (cell battery life). However, by addition of the hydrophobized CeNF, the cell battery capacity and the cycle characteristics (cell battery life) can be improved.