Silicon Electrode Slurry with Cellulose Fibers for Cycle Adhesion
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Solution Overview
Problem
Non-aqueous secondary batteries, such as lithium-ion batteries, face challenges with adhesion between the electrode active material and the current collector, leading to reduced discharge capacity and cycle durability due to expansion and contraction during charging and discharging.
Innovation Solution
A slurry composition containing cellulose fibers with specific length and diameter, combined with silicon and carbonaceous particles, and a carboxymethyl-group-containing cellulose ether, enhances adhesion and maintains high discharge capacity and durability by forming a tangled structure that absorbs expansion and contraction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If conventional binders like PVDF are used to ensure mechanical strength and adhesion, then the electrode maintains structural integrity during expansion and contraction, but the cost increases and environmental adverse effects worsen due to required organic solvents
Solution Approach 1:
The invention changes the chemical composition parameters of the binder system by using carboxymethyl cellulose (CMC) with specific degree of substitution (0.3-1.5) and molecular weight (10,000-500,000), replacing conventional PVDF binders. This parameter change enables the use of water as solvent instead of organic solvents like NMP, thereby reducing environmental adverse effects and cost while maintaining or improving adhesion strength through optimized cellulose ether properties
Solution Approach 2:
The invention employs carboxymethyl cellulose, a inexpensive and environmentally benign material, as the binder component. CMC can be easily synthesized from cellulose and degrades naturally, replacing expensive and environmentally problematic PVDF binders that require costly organic solvents for processing. This substitution reduces both material cost and environmental impact while achieving the required binding function
2Quantity of substance
If electrode materials with high capacity are used to increase energy density, then the battery capacity increases, but adhesion between electrode coating layer and current collector deteriorates due to expansion and contraction during charging and discharging
Solution Approach 1:
The invention optimizes the physical and chemical parameters of the binder system by selecting carboxymethyl cellulose with specific degree of substitution (0.3-1.5) and molecular weight (10,000-500,000). These parameter optimizations enable the binder to accommodate the expansion and contraction of high-capacity electrode materials during cycling while maintaining strong adhesion to the current collector, thus allowing use of high-capacity materials without adhesion failure
Solution Approach 2:
The invention creates a composite binder system combining carboxnymethyl cellulose (providing adhesion and flexibility) with starch (providing mechanical strength and cost reduction). This composite material approach allows the electrode structure to flexibly accommodate volume changes of high-capacity active materials while maintaining integrity and adhesion, enabling higher energy density without sacrificing structural stability
3Strength
If CMC with high degree of etherification is used to improve adhesion, then the binding strength increases, but the discharge capacity and cycle durability fail to meet recent higher demands
Solution Approach 1:
The invention optimizes the degree of substitution of carboxnymethyl cellulose to a specific range (0.3-1.5) rather than using high degree of etherification alone. This parameter optimization balances adhesion properties with flexibility, allowing the binder to maintain strong bonding while accommodating electrode expansion and contraction during cycling, thus improving both adhesion strength and cycle durability simultaneously
Solution Approach 2:
The invention combines carboxnymethyl cellulose with starch in a composite binder system. The starch component provides additional mechanical strength and flexibility, complementing the adhesive properties of CMC. This composite approach creates a more robust binder that maintains adhesion strength while providing the flexibility needed for high-capacity materials, thereby improving discharge capacity retention over cycles
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 proposed solution significantly improves discharge capacity retention and maintains high adhesion to the current collector, even with materials that exhibit large expansion and contraction, enhancing the energy density and cycle durability of the battery.
Implementation Method 1
forming a tangled structure that absorbs expansion and contraction
Implementation Method 2
enhances adhesion and maintains high discharge capacity and durability by forming a tangled structure
Data Source
AI summary
An electrode slurry contains (A) a cellulose fiber and (C) an electrode active material, the electrode active material (C) contains at least a silicon particle and may contain a silicon particle and a carbonaceous particle. The slurry may further contain (B) a carboxymethyl-group-containing cellulose ether or a salt thereof. The average fiber length L (1 to 750 µm) of the cellulose fiber (A) is larger than the average particle size DSi (1 nm to 1 µm) of the silicon particle as the electrode active material (C). The average particle size ratio L/DSi is 5 to 15000. The electrode slurry can improve a discharge capacity and is useful for forming an electrode of a non-aqueous secondary battery (lithium-ion secondary battery) that can maintain a high discharge capacity after repeated charging and discharging.