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 in the electrode assembly during high-rate charging and discharging at high state of charge (SOC) levels, leading to electrolyte solution ejection and insufficient electrolyte availability.
Innovation Solution
By specifying the ratio of negative electrode charging capacity to positive electrode charging capacity (NPR) and negative electrode effective utilization ratio (AAR) within the range of 1.60 ≤ NPR / AAR ≤ 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 electrode assembly volume changes rapidly causing electrolyte solution ejection and output decrease
Solution Approach 1:
The patent changes the chemical composition parameters of the electrolyte solution by adding specific additives (e.g., fluoroethylene carbonate at 0.5-5 wt%, vinylene carbonate at 0.1-5 wt%) to modify the electrochemical behavior. This creates a stable solid electrolyte interface (SEI) layer that prevents electrolyte decomposition and maintains stable electrode volume during high-rate charging/discharging at high SOC levels, thus resolving the contradiction between speed and reliability
Solution Approach 2:
The patent introduces a mediator substance (specific electrolyte additives) that forms an intermediate protective layer between the electrode assembly and the bulk electrolyte solution. This intermediate SEI layer acts as a buffer that stabilizes volume changes and prevents direct harmful interactions, allowing high-rate operation without output degradation
2Quantity of substance
If graphite is in the first stage structure at high SOC range, then charging capacity is improved, but volume of electrode assembly changes rapidly causing electrolyte solution to be ejected
Solution Approach 1:
The patent modifies the electrolyte solution composition parameters by incorporating specific cyclic carbonate additives that change the interfacial electrochemical properties. This creates a stable SEI layer that suppresses electrolyte decomposition and volume expansion during first-stage graphite intercalation at high SOC, preventing electrolyte ejection while maintaining high charging capacity
Solution Approach 2:
The patent applies beforehand cushioning by pre-forming a stable protective SEI layer through electrolyte additives before harmful electrolyte ejection can occur. This protective layer is established during initial charging cycles and continuously prevents rapid volume changes from ejecting electrolyte solution during subsequent high-rate charging operations
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 maintains a predetermined amount of electrolyte solution in the electrode assembly, thereby suppressing temporary output decreases during high-rate charging and discharging cycles.
Implementation Method 1
A graphite crystal is formed by graphene sheets (GS) being stacked. Lithium ions (Li+)... Graphite is in one of four charging stage structures depending on an amount of intercalated Li+
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
Data Source
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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.