Graphite Anode Capacity Ratio for Stable High-SOC Battery Output
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Solution Overview
Problem
Nonaqueous electrolyte secondary batteries experience temporary output decreases due to rapid volume changes during high-rate charging and discharging at high state of charge (SOC) levels, leading to electrolyte solution ejection and insufficient electrolyte maintenance.
Innovation Solution
By specifying the ratio of negative electrode charging capacity to positive electrode charging capacity (NPR/AAR) within a range of 1.60 to 2.55, the battery is configured to maintain a stable second stage structure of graphite at SOC levels between 70% to 90%, minimizing volume changes and electrolyte loss.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If high-rate charging and discharging are performed at high SOC levels, then charging and discharging speed is improved, but output stability deteriorates due to temporary output decrease
Solution Approach 1:
The patent applies parameter changes by precisely controlling the negative electrode charging capacity within a specific range (0.90 to 1.05 times the positive electrode charging capacity) and managing the charging stage structure transitions. This parameter control prevents excessive volume changes of graphite during charging/discharging, thereby maintaining output stability while enabling high-rate charging and discharging operations
2Quantity of substance
If graphite is expanded during charging, then charging capacity is improved, but volume stability deteriorates causing electrolyte solution ejection
Solution Approach 1:
The patent applies beforehand cushioning by pre-controlling the negative electrode charging capacity to be within a specific range relative to the positive electrode capacity. This preventive measure cushions against excessive graphite expansion during charging, preventing electrolyte solution ejection while maintaining adequate charging capacity
3Productivity
If the ratio of negative electrode charging capacity to positive electrode charging capacity is increased, then charging efficiency is improved, but volume change control deteriorates
Solution Approach 1:
The patent applies parameter changes by defining an optimal range for the negative electrode charging capacity ratio (0.90 to 1.05 times the positive electrode capacity). This parameter optimization achieves high charging efficiency while maintaining volume change control by preventing excessive graphite expansion
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 during high-rate charging and discharging by maintaining a predetermined amount of electrolyte solution, ensuring stable battery performance.
Implementation Method 1
Lithium ions (Li+) are intercalated in gaps between the graphene sheets. As the amount of intercalated Li+ is increased, graphite is expanded.
Implementation Method 2
The reaction force represents force with which the electrode assembly presses a battery case (housing) when the battery is constrained in a predetermined dimension. It is considered that a change in reaction force reflects a change in volume of the electrode assembly.
Data Source
AI summary
A nonaqueous electrolyte secondary battery includes an electrode assembly and an electrolyte solution. The electrode assembly is impregnated with at least part of the electrolyte solution. The electrode assembly includes a positive electrode, a negative electrode, and a separator. The separator separates the positive electrode and the negative electrode from each other. The negative electrode includes a negative electrode active material. The negative electrode active material includes graphite. The following relation of a formula (1) is satisfied: “1.60≤NPR/AAR≤2.55”. “NPR” represents a ratio of a negative electrode charging capacity to a positive electrode charging capacity. “AAR” represents a ratio of an effective discharging capacity of the negative electrode to a total of a capacity corresponding to an amount of inactive lithium adhered to the negative electrode and the effective discharging capacity of the negative electrode.