Secondary Battery Electrode Balancing for Low-SOC Resistance
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Solution Overview
Problem
Lithium secondary batteries exhibit high internal resistance in low state-of-charge (SOC) regions, particularly between 20% to 30%, which hinders the required output characteristics when starting an engine in a hybrid vehicle.
Innovation Solution
The secondary battery design includes a positive electrode and a negative electrode with a capacity difference from the terminal potential of the positive electrode discharge curve to the terminal voltage of the battery discharge curve set between 14% to 26%, shifting the positive electrode potential to the high potential side to reduce internal resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the positive electrode potential is shifted to the high potential side to reduce internal resistance in the low SOC region, then the internal resistance is reduced, but the battery capacity is reduced
Solution Approach 1:
The invention changes the operating potential parameters of the positive electrode by selecting materials with higher potential characteristics (such as lithium nickel cobalt manganese oxide with specific composition ratios). This parameter change allows the positive electrode to maintain higher potential in the low SOC region, reducing internal resistance while the specific composition optimization prevents excessive capacity loss
Solution Approach 2:
The invention uses composite positive electrode materials combining multiple components (lithium nickel cobalt manganese oxide with specific ratios of Ni, Co, and Mn elements) to achieve a balance between high potential operation and maintained capacity. The composite structure allows the material to exhibit both high potential characteristics and good capacity retention
2Reliability
If the negative electrode irreversible capacity is made larger than the positive electrode irreversible capacity to reduce internal resistance, then the internal resistance is reduced, but the capacity of the secondary battery is reduced
Solution Approach 1:
The invention optimizes the irreversible capacity parameter by controlling the composition ratios of the positive electrode material (specifically maintaining Ni content at 0.10-0.30, Co at 0.10-0.30, and Mn at 0.30-0.60 in lithium nickel cobalt manganese oxide). This parameter optimization ensures the positive electrode irreversible capacity remains appropriately balanced relative to the negative electrode, reducing internal resistance while preserving overall battery capacity
Data Source
AI summary
A conventional secondary battery has a problem that an internal resistance is very high in a low SOC region and necessary output cannot be taken out. In a secondary battery including a positive electrode and a negative electrode, a capacity difference from a terminal potential of a positive electrode discharge curve to a terminal voltage of a battery discharge curve of the secondary battery with respect to a discharge capacity of the secondary battery is 14% to 26%.