Hard Carbon Anode Porosity and Electrolyte Conductivity for Capacity Release
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Solution Overview
Problem
The low capacity per gram of graphite-based negative electrode materials in batteries limits energy density, and hard carbon materials suffer from increased impedance in low-charge states, leading to voltage rebound and incomplete capacity release, which reduces energy density.
Innovation Solution
A negative electrode active material layer with a porosity of 20% to 60% and a high-kinetic electrolyte with conductivity of 8 mS/cm to 14 mS/cm, combined with a discharge cut-off voltage of 1V to 2V, is used to enhance electrolyte storage and reduce impedance, thereby improving energy density and cycle performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If hard carbon materials are used as negative electrode active material to increase capacity per gram, then energy density is improved, but impedance increases in low-charge state causing voltage rebound and incomplete capacity release
Solution Approach 1:
The patent applies porous hard carbon materials with controlled pore structures to increase the capacity per gram while maintaining low impedance. The porous structure provides additional storage sites for lithium ions, increasing the quantity of substance (capacity) without significantly increasing impedance, thus resolving the contradiction between capacity and impedance stability.
Solution Approach 2:
The patent changes key parameters of the hard carbon material including pore size distribution, surface area, and crystalline structure to optimize both capacity and impedance characteristics. By adjusting these parameters, the material achieves high capacity per gram while maintaining stable impedance during charging cycles.
2Quantity of substance
If discharge cut-off voltage is reduced to release residual capacity, then energy density is improved, but voltage rebound increases due to high impedance in low-charge state
Solution Approach 1:
The porous structure of the hard carbon material enables efficient lithium ion transport even at low charge states, reducing impedance and minimizing voltage rebound. This allows the discharge cut-off voltage to be reduced to release residual capacity without suffering from severe voltage rebound, thus improving energy density.
Solution Approach 2:
The patent employs composite hard carbon structures combining different morphologies (spheroidal, flake-like, rod-like) with optimized pore distributions. This composite approach enables the material to maintain low impedance across a wide voltage range, allowing reduced cut-off voltage operation with minimal voltage rebound.
3Duration of action of stationary object
If porosity of negative electrode active material layer is increased to improve electrolyte storage capacity, then cycle performance is improved, but device complexity increases
Solution Approach 1:
The patent utilizes porous hard carbon materials with optimized pore structures that naturally provide excellent electrolyte storage capacity and ion transport channels. The porous structure itself serves multiple functions (electrolyte storage, ion transport, structural stability) without requiring additional complex components, thus improving cycle performance while avoiding excessive device complexity.
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 solution increases energy density and reduces voltage rebound by enhancing electrolyte retention and reducing impedance, resulting in improved high-temperature cycle performance and efficient capacity release.
Implementation Method 1
the electrolyte has a conductivity of 8 mS/cm to 14 mS/cm
Implementation Method 2
the negative electrode active material layer comprises hard carbon
Data Source
AI summary
An electrochemical device includes a negative active material layer and an electrolyte. The negative active material layer comprises hard carbon. The negative active material layer has a porosity of 20% to 60%. The electrolyte has a conductivity of 8 mS/cm to 14 mS/cm.