Bimodal Graphite Negative Electrode for Fast Charging
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Solution Overview
Problem
Lithium secondary batteries face limitations in high-output and high-capacity characteristics due to the use of graphite as negative electrode material, which suffers from low packing density, slow lithium ion insertion rates, and increased internal resistance during high-temperature storage, leading to reduced capacity and output.
Innovation Solution
A bimodal negative electrode active material comprising small and large particles, where the large particles have a carbon coating layer and the small particles do not, with a specific weight ratio and particle diameter distribution, enhancing bulk density and conductivity for improved charging performance and lifespan.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Duration of action of stationary object
If graphite is used as negative electrode material, then service life is extended and price is reduced, but capacity is limited to 372 mAh/g and output characteristics are poor
Solution Approach 1:
The negative electrode active material is divided into two distinct particle size groups: small particles (D50: 3-10 μm) and large particles (D50: 15-30 μm). This segmentation allows small particles to provide high capacity and fast lithium ion insertion/extraction, while large particles maintain structural stability and long service life, resolving the contradiction between capacity and service life.
2Ease of manufacture
If graphite has plate-like structure, then manufacturing is simplified, but packing density is low and grain orientation is poor
Solution Approach 1:
The invention changes the particle size parameter by introducing a bimodal distribution with small particles (D50: 3-10 μm) and large particles (D50: 15-30 μm). The small particles fill the voids between large particles, increasing packing density from the conventional single-size graphite to a higher density configuration, while maintaining the ease of manufacturing through standard granulation processes.
3Duration of action of moving object
If graphite is stored at high temperature for long period, then battery operates continuously, but internal resistance increases and capacity is reduced
Solution Approach 1:
The negative electrode uses a composite structure of small particles and large particles with different properties. The small particles provide high reactivity and fast ion transport, while the large particles provide structural stability. This composite approach prevents the increase in internal resistance during high-temperature storage, maintaining reliability during continuous operation.
4Speed
If small particles are used, then lithium ion insertion rate is fast, but resistance increases during high-temperature storage
Solution Approach 1:
The invention merges small particles (providing fast lithium ion insertion rate) with large particles (providing resistance stability). The small particles (D50: 3-10 μm) enable fast charging performance, while the large particles (D50: 15-30 μm) maintain low resistance during high-temperature storage, achieving both speed and reliability simultaneously.
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 bimodal structure achieves high-density electrodes with reduced resistance, enabling efficient lithium ion insertion and desorption, thus improving fast charging performance and long-term stability at high temperatures.
Implementation Method 1
The large particles may include a carbon coating layer on a surface of the secondary particles
Implementation Method 2
has a long diffusion distance through between a graphite basal plane, so its capacity is limited
Data Source
AI summary
Provided is a negative electrode active material for a secondary battery including an active material in a bimodal form including small particles and large particles, in which the small particles are primary particles, and the large particles are secondary particles formed by granulating the primary particles.