SiOx Negative Electrode Dual Carbon Coating
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Solution Overview
Problem
Increasing the capacity and suppressing capacity drop during charging and discharging in nonaqueous electrolyte secondary batteries is a challenge, particularly for negative electrodes using silicon oxides (SiOx) which have low conductivity.
Innovation Solution
A negative electrode comprising SiOx particles with a two-layer carbon coating, where the first coating is less crystalline to facilitate a stable SEI film and the second coating is highly crystalline for enhanced conductivity, combined with a binder having a limited number of etherifying agent moieties to prevent aggregation and improve adhesion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If SiOx particles are used as negative electrode material to increase capacity, then lithium ion storage capacity is improved, but electrical conductivity deteriorates
Solution Approach 1:
The patent uses composite materials by coating SiOx particles with carbon to create a composite structure that combines the high lithium ion storage capacity of SiOx with the high electrical conductivity of carbon, thereby resolving the contradiction between capacity and conductivity
Solution Approach 2:
The patent applies local quality by creating a carbon coating only on the surface of SiOx particles, maintaining the bulk properties of SiOx for high capacity while adding conductive carbon only where needed at the surface to improve electrical conductivity
2Reliability
If carbon coating is applied to SiOx particles to enhance conductivity, then electrical conductivity is improved, but cycle characteristics deteriorate
Solution Approach 1:
The patent applies parameter changes by controlling the crystallinity of the carbon coating, using a specific crystallinity range (0.3 to 0.7) that balances electrical conductivity with cycle stability, preventing excessive coating that would harm long-term performance
Solution Approach 2:
The patent uses local quality by creating a dual-layer carbon coating structure with different crystallinity levels - a first carbon layer with lower crystallinity for conductivity and a second carbon layer with higher crystallinity for structural stability during cycling
3Strength
If binder with etherifying agent moieties is used to improve adhesion, then adhesion is improved, but aggregation occurs
Solution Approach 1:
The patent applies parameter changes by controlling the etherification degree of the binder within a specific range (0.01 to 0.8), optimizing the balance between adhesion strength and resistance to aggregation by adjusting the chemical composition parameters of the binder
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 results in a high-capacity nonaqueous electrolyte secondary battery with excellent cycle characteristics and minimal capacity drop, achieved through the synergistic effects of improved conductivity and adhesion.
Implementation Method 1
a first carbon coating based on less crystalline carbon is disposed on the surface of the SiOx particles... This configuration probably facilitates the formation of a quality SEI film on the surface of the SiOx particles
Implementation Method 2
a second carbon coating which includes highly crystalline carbon is disposed on the first carbon coating, and thereby the conductivity of the first negative electrode active material is enhanced
Implementation Method 3
the use of a binder which has at least one of a carboxyl group and a hydroxyl group and has an average number of etherifying agent moieties present per unit molecule of not more than 0.8... enhances the adhesion among the materials constituting the mixture layer
Data Source
AI summary
A negative electrode for nonaqueous electrolyte secondary batteries is provided which includes SiOx and allows the cycle characteristics of batteries to be enhanced. A negative electrode according to an example embodiment includes a negative electrode current collector and a negative electrode mixture layer disposed on the current collector. The negative electrode mixture layer includes SiOx (0.5≤x≤1.5) particles having a carbon coating on a particle surface, carbonaceous active material particles, and a compound having at least one of a carboxyl group and a hydroxyl group and having an average number of etherifying agent moieties present per unit molecule of not more than 0.8. The carbon coating includes a first coating disposed on the surface of the SiOx and a second coating disposed on the first coating and including carbon having higher crystallinity than the carbon forming the first coating.