Negative Electrode Tortuosity for Stable High-Rate Battery Output
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Solution Overview
Problem
Nonaqueous electrolyte secondary batteries experience temporary output decreases after high-rate charging/discharging due to imbalance in electrolyte solution ejection and absorption, leading to insufficient electrolyte supply for charging/discharging reactions.
Innovation Solution
The battery design incorporates a negative electrode active material layer with an average tortuosity ratio of 1.5 to 2.5, formed by adjusting slurry kneading time, aspect ratio of particles, and ratio of large-aspect-ratio particles, which creates a reasonably complex pore structure to maintain electrolyte balance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If high-rate charging/discharging is continuously performed, then battery power output increases, but electrolyte solution is excessively ejected from the negative electrode active material layer causing temporary output decrease
Solution Approach 1:
The negative electrode active material layer is designed with a controlled pore structure characterized by a tortuosity ratio of 1.1 to 2.0. This porous structure allows the layer to absorb and retain electrolyte solution within its pores, preventing excessive ejection during high-rate charging/discharging while still permitting ion transport necessary for high power output
Solution Approach 2:
The tortuosity ratio of the negative electrode active material layer is optimized to a specific range (1.1 to 2.0). This parameter change controls the balance between electrolyte retention and ion transport, enabling the layer to maintain sufficient electrolyte during rapid charging/discharging cycles without sacrificing power output capability
2Speed
If high-rate charging/discharging is continuously performed, then charging speed increases, but electrolyte solution absorption is insufficient leading to output decrease
Solution Approach 1:
The negative electrode active material layer is pre-configured with an optimized pore structure and tortuosity ratio before battery operation. This preliminary structural design enables the layer to rapidly absorb and retain electrolyte solution at the start of charging/discharging cycles, ensuring sufficient electrolyte quantity even during high-speed charging without requiring gradual buildup
3Loss of substance
If tortuosity ratio is increased to retain electrolyte, then electrolyte ejection is suppressed, but ion migration resistance increases
Solution Approach 1:
The tortuosity ratio is optimized to a specific range (1.1 to 2.0) that balances two competing requirements: higher tortuosity retains electrolyte better while lower tortuosity allows faster ion migration. This precise parameter control enables simultaneous achievement of electrolyte retention and high ion migration efficiency
Solution Approach 2:
The pore structure within the negative electrode active material layer is designed with specific local characteristics including controlled tortuosity and pore size distribution. This local structural optimization ensures that electrolyte retention and ion migration pathways are both satisfied within the same material layer
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
This configuration effectively suppresses temporary output decreases after high-rate charging/discharging by maintaining a predetermined amount of electrolyte solution in the active material layer, ensuring stable battery performance.
Implementation Method 1
The negative electrode active material particles are expanded during charging and are contracted during discharging. Therefore, the negative electrode active material layer is also expanded during charging and is also contracted during discharging.
Implementation Method 2
When the negative electrode active material layer is expanded, the gap between the negative electrode active material particles is narrowed, with the result that the electrolyte solution is ejected from the negative electrode active material layer. When the negative electrode active material layer is contracted, the gap between the negative electrode active material particles is widened, with the result that the electrolyte solution is absorbed into the negative electrode active material layer.
Implementation Method 3
When high-rate charging/discharging is continuously repeated, the negative electrode active material layer is rapidly expanded and contracted in a repeated manner. As a result, the negative electrode active material layer is moved like a pump.
Data Source
AI summary
In a cross section parallel to a thickness direction of a negative electrode active material layer, an average tortuosity ratio is 1.5 to 2.5. The average tortuosity ratio is calculated by the following formula: “R=B/A”. In the formula, “R” represents the average tortuosity ratio. “B” represents an average value of lengths of shortest routes each extending from a contact point between a negative electrode substrate and a negative electrode active material particle to a surface of the negative electrode active material layer along contour lines of a plurality of negative electrode active material particles. “A” represents an average value of a thicknesses of the negative electrode active material layer.