Natural Graphite Negative Electrode Porosity for Input Performance
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Solution Overview
Problem
Nonaqueous electrolyte energy storage devices face a decrease in input performance when the porosity of the negative active material layer is too low, particularly when using natural graphite, due to reduced void volume and electrolyte retention, limiting their energy density.
Innovation Solution
A negative electrode design with natural graphite particles having an internal void ratio of 2% or less, pore volume of 7.8 nm or less of 0.0030 cm³/g, and porosity of 35% to 60%, enhancing electrolyte retention and input performance across a wide range of porosities.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the porosity of the negative active material layer is decreased to increase energy density, then the volume of voids between particles decreases, but the amount of nonaqueous electrolyte retained in the voids is reduced, causing input performance to decrease
Solution Approach 1:
The patent utilizes the porous structure of natural graphite particles, specifically controlling the internal void ratio to be 2% or less and the pore volume of pores with size of 7.8 nm or less to be 0.0030 cm³/g or less. This controlled porosity allows the material to retain sufficient electrolyte while achieving high energy density, resolving the contradiction between energy density and input performance.
Solution Approach 2:
The patent changes the physical parameters of the natural graphite particles by precisely controlling the internal void ratio and pore volume. By adjusting these parameters, the material maintains optimal electrolyte retention while achieving the desired energy density, thereby improving both energy density and input performance simultaneously.
2Volume of stationary object
If natural graphite is used as the negative active material to increase void volume, then the volume of voids between particles increases, but the input performance significantly decreases due to reduced electrolyte retention
Solution Approach 1:
The patent applies the porous materials principle by carefully controlling the internal structure of natural graphite particles. The internal void ratio is limited to 2% or less and the pore volume of small pores (7.8 nm or less) is limited to 0.0030 cm³/g or less. This controlled porosity ensures that while void volume is present for energy density, the structure still retains sufficient electrolyte for good input performance.
Solution Approach 2:
The patent applies local quality by creating different void characteristics within the natural graphite particles. By controlling the internal void ratio and pore size distribution locally within the particles, the material achieves optimal balance between void volume for energy storage and electrolyte retention for input performance.
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 design increases input performance of the nonaqueous electrolyte energy storage device by maintaining electrolyte retention and utilizing the higher crystallinity of natural graphite, even at lower porosities, thereby improving energy density and efficiency.
Implementation Method 1
the volume of voids between the negative active material particles decreases, whereby the amount of the nonaqueous electrolyte retained in the voids is reduced
Data Source
Figure 1~2
AI summary
A negative electrode for a nonaqueous electrolyte energy storage device according to one aspect of the present invention includes a negative active material layer including negative active material particles, in which the negative active material particles include natural graphite particles, an internal void ratio of the negative active material particles is 2% or less, a pore volume of pores having a pore size of 7.8 nm or less in the negative active material particles is 0.0030 cm3/g or less, and a porosity of the negative active material layer is 35% or more and 60% or less.