Double Carbon-Coated Graphite Anode for Fast-Charging Capacity
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Solution Overview
Problem
Lithium secondary batteries face challenges with natural graphite negative electrodes, which degrade due to increased alignability upon pressing, leading to poor rapid charge characteristics and capacity issues.
Innovation Solution
A negative electrode active material is developed with a graphite core coated by two carbon layers: a first carbon coating layer with higher crystallinity and a second layer with lower crystallinity, formed through specific heat treatments to optimize lithium ion infiltration and intercalation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If natural graphite is pressed to improve density and capacity, then capacity per unit weight is improved, but alignability of graphene layers increases causing degradation of lithium ion intercalation/deintercalation characteristics
Solution Approach 1:
The carbon coating is divided into two distinct layers with different crystallinities. The first layer (closer to graphite core) has higher crystallinity (30-60%) while the second layer (outer layer) has lower crystallinity (10-30%). This segmentation allows each layer to perform its specific function: the inner layer provides structural stability and capacity, while the outer layer facilitates rapid lithium ion transport.
Solution Approach 2:
Different regions of the carbon coating are assigned different local properties. The inner carbon layer has higher crystallinity to maintain structural integrity and provide high capacity, while the outer carbon layer has lower crystallinity to reduce alignability and enhance lithium ion intercalation kinetics. This local quality differentiation resolves the contradiction between capacity and rapid charge characteristics.
2Reliability
If carbon coating amount is increased to improve initial efficiency, then initial efficiency is improved, but rapid charge characteristics degrade due to aggregation
Solution Approach 1:
The carbon coating is segmented into two layers with different crystallinities and thicknesses. The inner layer (higher crystallinity) provides structural foundation, while the outer layer (lower crystallinity) with controlled thickness of 1-5 μm ensures rapid charge characteristics. This segmentation prevents aggregation while maintaining high initial efficiency.
Solution Approach 2:
The carbon coating is designed as a composite structure combining two types of carbon materials with different crystallinities. This composite approach allows the material to simultaneously achieve high initial efficiency (through sufficient carbon coating) and excellent rapid charge characteristics (through the low-crystallinity outer layer that prevents aggregation).
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 approach enhances initial efficiency and rapid charge characteristics by controlling crystallinity and preventing aggregation, thereby improving battery performance and capacity.
Implementation Method 1
a first carbon coating layer surrounding the outside of the graphite core; and a second carbon coating layer surrounding the outside of the first carbon coating layer
Implementation Method 2
shows excellent electrode cycle life by virtue of significantly reversible charge/discharge behaviors derived from the monoaxial alignability of a graphene layer
Data Source
AI summary
Disclosed is a negative electrode active material, including: a graphite core; a first carbon coating layer surrounding the outside of the graphite core; and a second carbon coating layer surrounding the outside of the first carbon coating layer, wherein the second carbon coating layer has a lower crystallinity as compared to 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.