Carbon Anode Material with Bimodal Particles for Cycle Retention
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Solution Overview
Problem
Current negative electrode materials for lithium-ion secondary batteries, such as those described in Patent Literature 1, do not adequately achieve high capacity retention and low DCR retention rates after 500 cycles, indicating a need for improved cycle characteristics.
Innovation Solution
A carbon material with specific surface area of 10 m2/g or less, a particle size distribution peak number of 2 or more, and a calculated number of particles (Ne) of 700 or more, which maintains electrical contact between particles, thereby enhancing cycle and DCR retention rates.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the density of the active material layer is increased to increase capacity, then the capacity increases, but the irreversible charge/discharge capacity increases due to material destruction
Solution Approach 1:
The invention changes the particle size distribution parameters of the carbon material, specifically controlling the volume-based average particle size to 3 μm or more and the number of peaks in particle size distribution to 2 or more. This parameter optimization reduces material destruction during initial cycles while maintaining high capacity, resolving the contradiction between increasing capacity and preventing irreversible capacity loss.
Solution Approach 2:
The invention uses composite carbon materials with specific particle size distributions, combining different sized particles to create a structure where larger particles provide structural stability and smaller particles fill gaps. This composite structure reduces material destruction and irreversible capacity while maintaining high overall capacity.
2Quantity of substance
If conventional carbon materials are used to achieve high capacity, then capacity increases, but cycle characteristics deteriorate after 500 cycles
Solution Approach 1:
The invention optimizes specific parameters including volume-based average particle size (3 μm or more), number of peaks in particle size distribution (2 or more), and specific surface area (10 m²/g or less). These parameter changes maintain high capacity while significantly improving cycle characteristics, achieving both high capacity retention and low DCR retention rate after 500 cycles.
3Reliability
If the specific surface area is increased to improve electrical contact, then electrical contact improves, but the number of peaks in particle size distribution increases
Solution Approach 1:
The invention optimizes the balance between specific surface area (10 m²/g or less) and particle size distribution peaks (2 or more). By controlling these parameters together, the invention achieves adequate electrical contact while maintaining a manageable particle size distribution structure, resolving the contradiction between improving electrical contact and controlling particle distribution complexity.
Data Source
AI summary
An object of the present invention is to provide a carbon material that achieves both a high capacity retention rate and a low DCR retention rate even after 500 cycles, and a secondary battery using the same. The gist of the present invention is as follows. A carbon material wherein a number of peaks in the particle size distribution obtained from flow type-particle image analysis is 2 or more, a number of particles Ne calculated by the following formula (1) is 700 or more, and a specific surface area is 10 m2/g or less. A secondary battery including a positive electrode, a negative electrode, and an electrolyte, wherein the negative electrode comprises a current collector and a negative electrode active material layer disposed on the current collector, and wherein the negative electrode active material layer contains this carbon material.Ne=No×F (1)(In formula (1), No is a number of particles of the carbon material obtained from the flow type-particle image analysis. F (%) is a particle frequency of the carbon material having a particle size of less than 3 μm obtained from the flow type-particle image analysis.)