Graphite Negative Electrode Particle Size Control for Lithium-Ion Capacitors
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Solution Overview
Problem
Lithium-ion capacitors face challenges in energy density, output density, and cycle durability, which are unsatisfactory compared to other next-generation electricity storage devices.
Innovation Solution
A negative electrode active material made of graphite with specific particle size distribution, where D50 is between 0 and 4.0 µm and the difference between D90 and D10 is less than or equal to 7.0 µm, is used to enhance the energy and output densities and cycle durability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If graphite with conventional particle size is used for negative electrode active material, then manufacturing is easier, but energy density and output density are insufficient
Solution Approach 1:
The patent applies parameter changes by optimizing the particle size distribution parameters (D50 and D90-D10) of graphite to specific ranges. This transforms the conventional approach of using arbitrary graphite sizes into a precise parameter-controlled system that maximizes energy density and output density while maintaining manufacturability.
Solution Approach 2:
The patent implements local quality by creating different particle size zones within the graphite distribution. By controlling the proportion of fine particles (D50 ≤ 4.0 μm) versus coarser particles, the electrode achieves local optimization where fine particles enhance energy density in contact regions while coarser particles provide structural stability.
2Reliability
If graphite with narrow particle size distribution is used, then output density and cycle durability are improved, but mixing property with binder during electrode formation deteriorates
Solution Approach 1:
The patent changes the particle size distribution parameters to achieve a balanced state. By setting D50 ≤ 4.0 μm and D90-D10 ≤ 7.0 μm, it finds the optimal parameter range that simultaneously improves cycle durability through better structural stability and maintains adequate mixing properties for electrode formation.
Solution Approach 2:
The patent applies partial action by not requiring complete uniformity in particle size distribution. Instead of using monodisperse particles that would ensure perfect mixing, it allows a controlled distribution range that provides sufficient mixing while achieving the desired durability improvements.
3Quantity of substance
If graphite with larger particle size is used, then self-discharge is reduced, but energy density and charging/discharging efficiency deteriorate
Solution Approach 1:
The patent applies parameter changes by optimizing the particle size parameters to a specific range that balances competing effects. The D50 ≤ 4.0 μm parameter ensures sufficient surface area for high energy density and efficient charging/discharging, while the controlled D90-D10 distribution minimizes excessive fine particles that would cause self-discharge.
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 use of graphite with these specific particle size characteristics improves the energy density, output density, and cycle durability of lithium-ion capacitors, ensuring stable and high electric power output over a wide charging/discharging range.
Implementation Method 1
graphite powder having a particle size of less than 10 μm is not used as a negative electrode material which can absorb and desorb lithium
Implementation Method 2
an electrolyte having an aprotic organic solvent of a lithium salt
Data Source
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AI summary
The invention provides a negative electrode material for use with a lithium-ion capacitor (10), which is high in energy density, output density and excellent in durability. When graphite of which an average distance between 002 lattice planes thereof is within a range from 0.335 nm to 0.337 nm is used for an active material of a negative electrode (12) of a lithium-ion capacitor (10), the energy density of the capacitor is increased. The output characteristic and the cycle durability can be improved when D10, D50 and D90 are set within predetermined ranges.