Si-Containing Battery Anode Binder and Electrolyte for Low Resistance
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Solution Overview
Problem
Non-aqueous electrolyte secondary batteries with Si-containing negative electrodes face issues of increased internal resistance and deteriorated cycle characteristics due to the expansion and contraction of Si-containing materials, which is exacerbated by the swelling of carboxymethyl cellulose (CMC) binders used to mitigate these effects.
Innovation Solution
Incorporating a binder comprising carboxyalkyl cellulose or its salts, such as sodium carboxymethyl cellulose, with a high weight-average molecular weight and controlled degree of neutralization, in combination with a lithium salt like lithium bis(fluorosulfonyl)imide (LFSI) in the electrolyte, to maintain binding force and reduce swelling, thereby minimizing internal resistance and enhancing cycle characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If CMC binder is used to suppress deterioration of cycle characteristics, then cycle characteristics are improved, but internal resistance increases due to swelling of CMC
Solution Approach 1:
The patent changes the molecular weight parameter of the CMC binder from conventional ranges to weight-average molecular weight of 200,000 or more (preferably 300,000 or more), which fundamentally alters the swelling behavior and binding characteristics of the CMC, resolving the contradiction between cycle stability and internal resistance
Solution Approach 2:
The patent specifies a controlled degree of neutralization (30-80%) for the CMC binder, creating localized optimal binding properties that maintain effectiveness during Si expansion/contraction cycles without excessive swelling, thus addressing both cycle characteristics and internal resistance issues
2Quantity of substance
If Si-containing material is used to improve capacity, then capacity is improved, but contact resistance increases due to expansion and contraction
Solution Approach 1:
The patent applies a coating layer to the Si-containing material particles before assembling the electrode, pre-establishing a protective interface that maintains contact stability during subsequent expansion and contraction cycles, preventing contact resistance increase while preserving high capacity
Solution Approach 2:
The patent uses composite structures where Si-containing particles are coated with other materials (such as carbon coatings or oxide layers), creating a composite material that combines the high capacity of Si with the structural stability and conductivity of the coating, thereby maintaining contact resistance while achieving high capacity
3Strength
If CMC binder is used to bind negative electrode particles, then binding force is improved, but viscosity increases making slurry preparation difficult
Solution Approach 1:
The patent changes the molecular weight parameter of CMC to weight-average molecular weight of 200,000 or more, which alters the rheological properties of the slurry, providing sufficient binding force while actually reducing viscosity compared to lower molecular weight CMC, thus resolving both binding strength and manufacturability issues
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 allows for a non-aqueous electrolyte secondary battery with high capacity and small internal resistance, while maintaining excellent cycle characteristics even with a small amount of binder, preventing viscosity increases and facilitating easier slurry preparation.
Implementation Method 1
When the negative electrode containing CMC is impregnated with an electrolyte, the CMC sometimes swells
Implementation Method 2
The electrolyte including a non-aqueous solvent, and a lithium salt dissolved in the non-aqueous solvent
Implementation Method 3
a negative electrode active material capable of electrochemically absorbing and releasing lithium
Data Source
AI summary
A non-aqueous electrolyte secondary battery including a positive electrode, a negative electrode, and an electrolyte. The negative electrode includes a negative electrode active material capable of electrochemically absorbing and releasing lithium, and a binder. The negative electrode active material includes a Si-containing material, and the binder includes at least one cellulose compound selected from the group consisting of a carboxyalkyl cellulose and a salt thereof. The electrolyte includes a non-aqueous solvent, and a lithium salt dissolved in the non-aqueous solvent. The lithium salt includes lithium bis(fluorosulfonyl)imide: LFSI.