Dual-Graphite Negative Electrode Structure for Fast-Charging Stability
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Solution Overview
Problem
Electrochemical apparatuses face challenges in balancing energy density and kinetic performance, with improvements in charge capacity and speed often leading to low gram capacity and poor cycling performance due to lithium precipitation.
Innovation Solution
The electrochemical apparatus features a negative electrode plate with a first layer of graphite having a thermal decomposition temperature of 800°C or higher and a second layer with a temperature between 500°C to 700°C, strategically designed to enhance kinetic performance while maintaining high energy density and cycling stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the charge capacity and charge speed of negative electrode active materials are improved, then the kinetic performance is enhanced, but the gram capacity decreases and cycling performance deteriorates due to lithium precipitation
Solution Approach 1:
The negative electrode active material is segmented into two distinct layers: a first layer with graphite having a thermal decomposition temperature of 800°C or higher, and a second layer with graphite having a thermal decomposition temperature of 500-700°C. This segmentation allows each layer to perform different functions - the first layer provides high gram capacity while the second layer enhances kinetic performance through faster lithium ion insertion/extraction, preventing lithium precipitation even at high charge speeds
Solution Approach 2:
Different regions of the negative electrode are assigned different properties through the two-layer structure. The first layer (with higher thermal decomposition temperature) is optimized for high gram capacity and structural stability, while the second layer (with lower thermal decomposition temperature) is optimized for fast kinetics and lithium ion transport. This local quality differentiation resolves the contradiction by allowing high charge speed in the second layer without compromising the overall gram capacity and cycling performance provided by the first layer
2Use of energy by moving object
If the charge capacity is increased, then the energy density is improved, but the gram capacity of negative electrode active materials decreases
Solution Approach 1:
The negative electrode active material is divided into two layers with different graphite properties. The first layer (higher thermal decomposition temperature ≥800°C) contributes to high gram capacity, while the second layer (lower thermal decomposition temperature 500-700°C) enhances kinetic performance and enables higher charge capacities to be achieved. Together, they achieve both high energy density and high gram capacity
Solution Approach 2:
The invention uses a composite structure of two types of graphite materials with different thermal decomposition characteristics. This composite negative electrode active material combines the advantages of both graphite types - the structural stability and high capacity of the first layer with the fast kinetics of the second layer - achieving both high energy density and high gram capacity simultaneously
Data Source
Figure 1
AI summary
An electrochemical apparatus includes a negative electrode plate, where the negative electrode plate includes a negative electrode current collector, a first layer, and a second layer, and the first layer is located between the negative electrode current collector and the second layer. Both the first layer and the second layer include graphite; a thermal decomposition temperature of the graphite in the first layer is A, and A is greater than or equal to 800°C; a thermal decomposition temperature of the graphite in the second layer is B, and B ranges from 500°C to 700°C; and 100°C ≤ A - B ≤ 500°C.