Composite Negative Electrode Active Material for Lithium Secondary Battery
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Solution Overview
Problem
Lithium secondary batteries face challenges with volume expansion of artificial graphite negative electrode materials during charging, leading to cracking and deterioration of capacity retention over time, which affects the battery's output and lifespan.
Innovation Solution
A composite negative electrode active material is developed, comprising a first carbon-based material with a medium particle diameter and a second carbon-based material with high strength and Young's modulus, positioned on the surface of the first material, which is formed through a process of mixing, aggregating, and sintering to create a core-shell structure with a carbon coating layer, effectively controlling volume expansion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If natural graphite is used as negative electrode active material, then energy density and energy capacity are improved, but capacity retention deteriorates due to cracking from volume expansion during charging
Solution Approach 1:
The patent uses a composite structure consisting of natural graphite particles coated with an artificial graphite layer. The natural graphite core provides high energy capacity, while the artificial graphite shell suppresses volume expansion and prevents cracking. This composite material combines the advantages of both materials to achieve high energy density while maintaining capacity retention.
Solution Approach 2:
The patent applies different properties to different parts of the negative electrode material. The core region uses natural graphite with high energy capacity, while the surface layer uses artificial graphite with low volume expansion characteristics. This local differentiation allows each region to perform its optimal function.
2Stability of the object's composition
If artificial graphite is used instead of natural graphite, then volume expansion is reduced, but energy density and energy capacity decrease
Solution Approach 1:
The patent creates a composite structure where natural graphite particles (high energy density) are coated with artificial graphite (high volume stability). This allows the material to achieve both high energy density from the natural graphite core and volume stability from the artificial graphite shell, resolving the contradiction between these two properties.
3Strength
If graphite particles are finely refined and mixed with binder to form base graphite material, then cracking is partially prevented, but volume expansion inhibition and lifetime characteristics are not sufficiently achieved
Solution Approach 1:
The patent goes beyond simple mixing with binders by creating a composite material where artificial graphite particles are coated on natural graphite particles. This structural approach provides superior crack resistance and volume expansion control compared to binder-based solutions, significantly improving lifetime characteristics.
Solution Approach 2:
The artificial graphite coating acts as a protective shell around the natural graphite particles. This shell is flexible enough to accommodate volume changes while providing mechanical support to prevent cracking, thereby improving both crack resistance and lifetime characteristics.
4Ease of manufacture
If conventional negative electrode materials are used, then manufacturing is simple, but output and rate characteristics are insufficient
Solution Approach 1:
The patent employs a composite structure of natural graphite and artificial graphite particles, which can be manufactured using conventional coating and sintering processes. This approach maintains ease of manufacture while significantly improving output and rate characteristics through the synergistic properties of the composite material.
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 composite material significantly reduces volume expansion, enhances discharge capacity, and improves cycle and rate characteristics, thereby extending the battery's lifespan and maintaining high output performance.
Implementation Method 1
a composite negative electrode active material having suppressed or reduced volume expansion
Implementation Method 2
A lithium secondary battery produces electrical energy by oxidation and reduction reactions of lithium ions which are intercalated/deintercalated in a positive electrode and a negative electrode
Implementation Method 3
sintering a mixture of the first carbon-based secondary particles and second carbon-based primary particles to form a composite negative electrode active material
Data Source
AI summary
A composite negative electrode active material includes: a first carbon-based material; and a second carbon-based material on a surface of the first carbon-based material, wherein the first carbon-based material and the second carbon-based material have respective particle diameters that are different from each other.