Graphite Negative Electrode Packing Structure for Faster Li-Ion Migration
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Solution Overview
Problem
Existing lithium secondary batteries face limitations in high output and capacity due to graphite's small interlayer distance, slow lithium ion insertion speed, and increased resistance at high temperatures, leading to decreased capacity and output characteristics.
Innovation Solution
A negative electrode active material layer comprising a mixture of 1st to nth negative electrode materials with specific particle size distributions and orientation indexes, optimized to form an optimized packing structure, minimizing pressure on active material particles and enhancing lithium ion migration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If graphite is used as negative electrode material, then cost and usage life are improved, but capacity and lithium ion insertion speed are limited due to small interlayer distance and long diffusion distance
Solution Approach 1:
The negative electrode active material is segmented into multiple particle sizes (first, second, third particle sizes) with different proportions. This segmentation creates a multi-scale structure where smaller particles provide shorter diffusion paths for lithium ions while larger particles maintain overall capacity, effectively resolving the contradiction between capacity and insertion speed.
Solution Approach 2:
Different regions of the electrode are assigned different particle size distributions. The electrode structure incorporates particles of varying sizes in specific proportions to optimize local properties: smaller particles in regions requiring fast lithium ion insertion while larger particles are distributed to maintain overall capacity, achieving local optimization of both capacity and insertion speed.
2Ease of manufacture
If graphite with plate structure is used, then cost is reduced, but lithium ion insertion speed decreases due to low packing density and poor particle orientation
Solution Approach 1:
The patent changes the particle size parameter by incorporating three different particle sizes with specific proportions. This parameter modification optimizes the packing density and particle orientation within the electrode structure, enabling faster lithium ion insertion while maintaining cost-effectiveness through continued use of graphite material.
3Quantity of substance
If graphite is stored at high temperature for long time, then internal resistance increases, but capacity and output characteristics are maintained initially
Solution Approach 1:
The multi-size particle segmentation creates a hierarchical structure that mitigates high-temperature degradation. Smaller particles are less susceptible to thermal stress and resistance increase, while larger particles maintain capacity. This segmented structure ensures that not all particles are equally affected by high-temperature storage, preserving both capacity and output characteristics over time.
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 optimized packing structure improves high temperature storage and life characteristics of secondary batteries by reducing internal resistance and maintaining effective lithium ion migration paths.
Implementation Method 1
a negative electrode for a secondary battery includes: a current collector; and a negative electrode active material layer which is formed on at least one surface of the current collector and includes a mixture of 1st to nth negative electrode active materials
Implementation Method 2
a long diffusion distance between graphite basal planes, and thus, has a limited capacity of 372 mAh/g
Data Source
AI summary
Provided are a negative electrode for a secondary battery and a secondary battery including the same. The negative electrode for a secondary battery according to an exemplary embodiment includes: a current collector; and a negative electrode active material layer which is formed on the current collector and includes a mixture of 1st to nth negative electrode active materials (n is a natural number of 2 or more), wherein the 1st to nth negative electrode active materials and the mixture thereof satisfy the following Relation 1: 1.05<DspanmixDspan1+Dspan2+⋯+Dspann/n<3.0.