Bimodal Artificial Graphite for Low-Temperature Battery Performance
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Solution Overview
Problem
Lithium secondary batteries face challenges with high charge transfer resistance due to the polycrystallinity of nanostructured negative electrode active materials, which hinders intercalation and deintercalation reactions and degrades battery performance at room and low temperatures.
Innovation Solution
A negative electrode active material is developed using a bimodal structure comprising artificial graphite with a large particle diameter (15 μm to 20 μm) and a small particle diameter (3 μm to 5 μm), where the larger particles are agglomerated with a carbon coating layer, and the two types are mixed in a specific weight ratio to reduce charge transfer resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If nano-sized negative electrode active material is prepared, then output characteristics are improved and diffusion rate of lithium ions is enhanced, but charge transfer resistance is increased due to polycrystallinity of nanostructure
Solution Approach 1:
The invention divides the negative electrode active material into two distinct particle size segments: micro-sized particles (3-5 μm) and nano-sized particles (0.5-2 μm). This segmentation allows each size range to fulfill different functions - the micro-sized particles provide stable structure and low charge transfer resistance, while the nano-sized particles enhance output characteristics and lithium ion diffusion rate. The bimodal particle size distribution resolves the contradiction by separating the conflicting requirements into different size categories that work synergistically.
Solution Approach 2:
The invention creates a composite negative electrode active material consisting of micro-sized artificial graphite particles and nano-sized artificial graphite particles in a specific weight ratio (80:20 to 95:5). This composite structure combines the advantages of both size ranges - the micro-sized particles contribute to low charge transfer resistance and structural stability, while the nano-sized particles provide high output characteristics and enhanced lithium ion diffusion. The composite material approach allows simultaneous achievement of apparently conflicting properties.
2Speed
If nano-sized negative electrode active material is prepared, then contact with electrolyte is facilitated and rapid electrochemical reaction is expected, but intercalation and deintercalation reactions of lithium ions become difficult due to SEI components
Solution Approach 1:
The invention segments the particle population into micro-sized and nano-sized categories, assigning different functional roles to each. The micro-sized particles (3-5 μm) serve as the primary intercalation/deintercalation sites with stable SEI interfaces, while the nano-sized particles (0.5-2 μm) provide rapid electrochemical reaction pathways. This segmentation prevents the SEI formation issues that plague pure nanostructures from affecting the entire material system.
Solution Approach 2:
The invention changes the particle size parameter to create a bimodal distribution, specifically controlling the weight ratio of micro-sized to nano-sized particles (80:20 to 95:5). By adjusting this size parameter distribution, the material achieves optimal balance between electrochemical reaction rate and intercalation/deintercalation ease. The presence of micro-sized particles with stable SEI interfaces compensates for the SEI-related difficulties in nano-sized particles.
3Stability of the object's composition
If graphite-based active material is used, then structural and electrical properties are maintained and reversibility is ensured, but charge transfer resistance is high at room temperature and low temperature
Solution Approach 1:
The invention segments the graphite particles into two size categories, where micro-sized particles (3-5 μm) maintain structural stability and electrical properties, while nano-sized particles (0.5-2 μm) reduce charge transfer resistance and improve low-temperature performance. The segmentation allows the system to simultaneously achieve compositional stability and low charge transfer resistance by distributing these functions across different size ranges.
Solution Approach 2:
The invention creates a composite graphite material with bimodal particle size distribution (micro-sized 3-5 μm and nano-sized 0.5-2 μm particles). This composite structure combines the structural and electrical stability of conventional graphite with the low charge transfer resistance characteristics of fine particles. The synergistic interaction between the two size ranges enables the material to maintain stability while achieving low charge transfer resistance at room and low temperatures.
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 effectively reduces charge transfer resistance, enhancing the output characteristics of lithium secondary batteries at both room and low temperatures by facilitating lithium ion intercalation and deintercalation.
Implementation Method 1
a graphite-based active material, which may ensure life characteristics of a lithium secondary battery due to excellent reversibility
Implementation Method 2
capable of reversibly intercalating and deintercalating lithium ions
Implementation Method 3
a carbon coating layer formed on a surface of the secondary artificial graphite particle
Implementation Method 4
pores present between nano-sized active material particles provide a space for the expansion of the electrode active material
Data Source
AI summary
The present invention relates to a negative electrode active material for a lithium secondary battery, which includes (A) first artificial graphite having an average particle diameter (D50) of 15 μm to 20 μm and (B) second artificial graphite having an average particle diameter (D50) of 3 μm to 5 μm, wherein the first artificial graphite (A) includes a secondary artificial graphite particle, in which at least one primary artificial graphite particle is agglomerated, and a carbon coating layer, and a weight ratio of the first artificial graphite to the second artificial graphite is in a range of 85:15 to 95:5, a negative electrode including the same, and a lithium secondary battery including the negative electrode.