Dual Carbon-Coated Graphite Anode for Fast-Charging Li-Ion Batteries
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Solution Overview
Problem
Conventional negative electrode materials, such as natural graphite, suffer from degradation of rapid charge characteristics due to increased alignability upon pressing, leading to degradation of lithium ion intercalation/deintercalation properties.
Innovation Solution
A negative electrode active material is developed with a graphite core surrounded by two carbon coating layers, where the outer layer has lower crystallinity than the inner layer, or the inner layer is made of soft carbon and the outer layer of hard carbon, with each layer having a specific weight percentage and formed through controlled heat treatments.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If natural graphite is pressed to improve density and handling, then particle alignability increases, but lithium ion intercalation/deintercalation characteristics degrade
Solution Approach 1:
The graphite particle is segmented into a core-shell structure with an inner graphite core and an outer carbon coating layer. This segmentation allows the core to maintain high crystallinity for capacity while the shell provides a less crystalline surface that facilitates lithium ion diffusion, resolving the contradiction between alignability and ion intercalation characteristics.
Solution Approach 2:
Different regions of the graphite particle are given different properties: the inner core has high crystallinity for structural stability and capacity, while the outer coating layer has lower crystallinity to enhance lithium ion diffusion. This local quality differentiation allows the particle to simultaneously achieve good alignability and rapid charge characteristics.
2Reliability
If a single carbon coating layer is applied to graphite, then lithium ion diffusion is improved, but rapid charge characteristics are not sufficiently enhanced
Solution Approach 1:
The carbon coating is segmented into two distinct layers with different crystallinities. The inner layer provides a transition zone while the outer layer with lower crystallinity offers excellent lithium ion diffusion pathways, together achieving superior rapid charge characteristics that a single uniform layer cannot provide.
Solution Approach 2:
The dual-layer carbon coating creates a composite structure where each layer contributes different properties. The combination of inner and outer carbon layers with varying crystallinities produces synergistic effects that enhance both lithium ion diffusion and rapid charge characteristics beyond what a single material could achieve.
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 carbon coating structure enhances rapid charge characteristics and prevents degradation of the battery's capacity and charge/discharge characteristics by facilitating easy lithium ion infiltration and maintaining optimal particle size for improved handling.
Implementation Method 1
subjecting the first mixture to a first heat treatment at a temperature ranging from 1,400° C. to 1,600° C. to obtain a first carbon coating layer on a graphite core; and mixing the graphite core having the first carbon coating layer with a second carbon precursor to obtain a second mixture; and subjecting the second mixture to a second heat treatment at a temperature ranging from 1,100° C. to 1,300° C. to form a second carbon coating layer on the first carbon coating layer
Data Source
AI summary
A negative electrode active material, including: a graphite core; a first carbon coating layer on the graphite core; and a second carbon coating layer on the first carbon coating layer, wherein a crystallinity of the second carbon coating layer is lower than a crystallinity of the first carbon coating layer, or the second carbon coating layer includes hard carbon and the first carbon coating layer includes soft carbon. A negative electrode including the negative electrode active material and a lithium secondary battery including the same are also disclosed.