Lithium Ion Negative Electrode Pore Structure for Electrolyte Penetration
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Solution Overview
Problem
The high packing density of negative electrode active material in lithium ion secondary batteries reduces non-aqueous electrolyte penetration, leading to degraded input-output characteristics and increased stress on the active material, causing cracking and reduced charge-discharge performance.
Innovation Solution
A negative electrode with a surface and interior pore structure, featuring pores with an average maximum diameter of 45 to 125 μm and a number density of 8 to 17 pores per cm², formed during the drying of the negative electrode material mixture slurry, using a binder like sodium salt of carboxymethyl cellulose to enhance electrolyte penetration and reduce stress on the active material.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the negative electrode active material is highly densely packed in the negative electrode material mixture layer, then the negative electrode capacity is increased, but the penetration of non-aqueous electrolyte into the layer is reduced
Solution Approach 1:
The invention introduces a porous structure into the negative electrode material mixture layer by forming pores during the drying process of the slurry. These pores, with specific size distributions (first pores: 10-50 μm, second pores: 50-150 μm), create channels that facilitate electrolyte penetration while maintaining high active material density in the solid matrix between pores, thus resolving the contradiction between capacity and electrolyte access
Solution Approach 2:
The invention changes the physical parameters of the electrode structure by controlling pore size distribution and density. By optimizing the number density of pores (8-17 pores/cm²) and their size ranges, the invention achieves a balance where sufficient electrolyte can penetrate through the layer to reach densely packed active material particles, improving both capacity utilization and rate performance
2Quantity of substance
If the negative electrode active material is highly densely packed, then the negative electrode capacity is increased, but the stress on the active material is increased causing cracking
Solution Approach 1:
The porous structure acts as a stress relief network within the densely packed active material layer. The pores provide void space that accommodates volume changes of active material particles during lithium insertion/extraction, reducing mechanical stress and preventing cracking while maintaining high overall density of active material in the electrode layer
Solution Approach 2:
The pores are formed beforehand during the drying process, creating a pre-computed stress relief architecture. This预先设计的孔隙结构 cushions the active material particles against stress during subsequent charge-discharge cycles, preventing cracking before it occurs while allowing high active material loading
3Quantity of substance
If recesses or grooves are formed on the surface of the negative electrode material mixture layer, then non-aqueous electrolyte retention at the surface is improved, but the penetration of electrolyte into the layer is reduced
Solution Approach 1:
Instead of forming surface-only recesses or grooves, the invention creates a three-dimensional porous network extending through the entire thickness of the negative electrode material mixture layer. This volumetric porous structure provides both surface electrolyte retention (through numerous small pores at the surface) and deep electrolyte penetration (through interconnected pores extending into the layer interior), simultaneously achieving both benefits
4Quantity of substance
If recesses or grooves are formed by die-pressing, then the surface structure is modified for electrolyte retention, but the negative electrode active material becomes more densely packed reducing electrolyte penetration
Solution Approach 1:
The porous structure is formed preliminarily during the drying process of the slurry, before the final pressing step. This timing allows the pores to be created when the material is still in a semi-plastic state, and subsequent pressing consolidates the structure without completely eliminating the pores. The result is a densely packed active material layer that retains an interconnected porous network for electrolyte penetration, achieving both high capacity and good electrolyte access
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 improves non-aqueous electrolyte penetration and retention, maintaining excellent input-output characteristics and charge-discharge performance while reducing the risk of active material cracking and layer separation.
Implementation Method 1
pores with an average maximum diameter R of 45 to 125 μm... formed during the drying of the negative electrode material mixture slurry
Data Source
AI summary
Provided is a negative electrode for lithium ion secondary batteries, which can enhance the penetration of non-aqueous electrolyte, and can improve the input-output characteristics. The negative electrode includes a negative electrode core material sheet, and a negative electrode material mixture layer supported thereon. The negative electrode material mixture layer includes negative electrode active material particles, and a binder. The negative electrode material mixture layer has a plurality of pores interspersed on the surface and in the interior of the negative electrode material mixture layer. The pores have an average maximum diameter R of 45 to 125 μm. The pores have a number density of 8 to 17 pores per 1 cm2 of the surface of the negative electrode material mixture layer or per 1 cm2 of a cross section in the plane direction of the negative electrode material mixture layer.