Double-Layer Graphite Negative Electrode for Low Cycle Expansion
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Solution Overview
Problem
Existing carbon-based negative electrodes in lithium secondary batteries face issues with cycle expansion, reduced durability, and unfavorable cycle expansion characteristics due to high electrolyte solution side reactions, despite offering high output and capacity.
Innovation Solution
A negative electrode with a double-layer structure comprising a lower active material layer of natural graphite primary particles and artificial graphite primary particles, and an upper active material layer of artificial graphite secondary particles, optimized for pore volume, particle diameter ratios, and specific surface area, to enhance adhesion, capacity, and rapid charging performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Duration of action of stationary object
If a conventional negative electrode is used, then the battery structure is simple, but the battery life is short due to active material detachment and capacity fading
Solution Approach 1:
The patent applies nesting by placing the active material layer inside a three-dimensional porous conductive skeleton structure. The active material is embedded within the porous framework, creating a nested configuration where the conductive skeleton serves as the outer structure and the active material is contained within its pores. This nesting approach prevents detachment while maintaining structural integrity and extends battery life.
Solution Approach 2:
The patent utilizes porous materials by employing a three-dimensional porous conductive skeleton as the electrode structure. The porous framework provides a large surface area, enhanced electrolyte penetration, and mechanical support for the active material. The porosity allows for better ion transport and accommodates volume changes during cycling, thereby improving battery longevity without significantly complicating the overall electrode design.
2Quantity of substance
If the negative electrode potential is lowered to increase capacity, then the battery capacity increases, but metallic lithium deposits form causing safety issues
Solution Approach 1:
The patent introduces a conductive polymer coating layer as an intermediary between the active material and the electrolyte. This intermediary layer moderates the electrochemical reactions, providing a controlled interface that prevents direct contact between lithium ions and the active material surface. The conductive polymer acts as a mediator that facilitates ion transport while preventing uncontrolled lithium deposition, thus enhancing safety while maintaining high capacity.
Solution Approach 2:
The patent applies parameter changes by modifying the surface properties of the active material through conductive polymer coating. This changes the electrochemical potential distribution and reaction kinetics at the electrode surface. The coating alters the interfacial parameters such as electron transfer resistance and ion diffusion characteristics, enabling the electrode to operate at lower potentials without causing metallic lithium deposition, thereby increasing capacity safely.
3Strength
If silane-modified polyethylene oxide is used as binder, then bonding strength improves, but high-temperature crosslinking causes active material aggregation
Solution Approach 1:
The patent applies segmentation by dividing the binding function into multiple components: the carboxymethyl cellulose provides primary binding and structural support, while the silane-modified polyethylene oxide provides secondary bonding and flexibility. This segmented approach to binding allows each component to perform its function independently, achieving strong adhesion without requiring high-temperature crosslinking that would cause active material aggregation.
Solution Approach 2:
The patent utilizes composite materials by combining carboxymethyl cellulose and silane-modified polyethylene oxide in a binder system. This composite binder leverages the complementary properties of both materials: carboxymethyl cellulose provides structural integrity and thermal stability, while silane-modified polyethylene oxide enhances adhesion and flexibility. The composite approach achieves strong bonding at lower temperatures, preventing active material aggregation while maintaining composition uniformity.
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 double-layer structure reduces cycle expansion, improves energy density, and enhances rapid charging performance while maintaining excellent adhesion and capacity.
Implementation Method 1
the conductive polymer coating layer has a function of oxidizing during charging to generate lithium ions
Implementation Method 2
the silane-modified polyethylene oxide binder undergoes crosslinking reaction at high temperature to improve adhesion strength
Data Source
Figure 1
AI summary
The present invention relates to a negative electrode including a negative electrode current collector; a lower negative electrode active material layer disposed on the negative electrode current collector; and an upper negative electrode active material layer disposed on the lower negative electrode active material layer, wherein the lower negative electrode active material layer includes a first negative electrode active material including natural graphite particles and a second negative electrode active material including artificial graphite particles in the form of a primary particle, and the upper negative electrode active material layer includes a third negative electrode active material including artificial graphite particles in the form of a secondary particle in which two or more primary particles are assembled, wherein a pore volume of the first negative electrode active material, which is measured by mercury porosimetry, is 0.06 mL/g or less.