Mixed-NP Cell Combination for Battery Overcharge Safety
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Solution Overview
Problem
Secondary batteries face challenges in cycle performance and safety performance due to potential overcharging, which can lead to safety risks and reduced cycle life.
Innovation Solution
A cell combination is designed with a first cell and a second cell, where the number of first cells is greater than or equal to the number of second cells, and specific ratios of lithium intercalation and deintercalation capacities are defined to limit voltage changes, thereby reducing overcharge and improving safety and cycle life.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If the NP ratio is limited to less than 1 to reduce negative electrode active material and lower cost, then manufacturing cost is reduced and space is saved for increased capacity, but voltage change becomes minor when SOC approaches saturation level, making the cell prone to overcharging and posing safety risks
Solution Approach 1:
The battery is divided into multiple cells with different NP ratios. Some cells have NP < 1 (first cells) for cost reduction, while others have NP ≥ 1 (second cells) for safety. This segmentation allows the system to simultaneously achieve cost reduction and safety improvement by distributing different functional roles across different cell groups.
Solution Approach 2:
The patent changes the NP ratio parameter across different cells in the battery system. By having some cells with NP < 1 and others with NP ≥ 1, the system optimizes the balance between cost (lower NP reduces negative electrode material) and safety (higher NP ensures adequate voltage change for overcharge protection).
2Reliability
If the NP ratio is increased to improve safety performance and prevent overcharging, then safety performance is improved, but the amount of negative electrode active material increases, raising cost and reducing capacity
Solution Approach 1:
The battery system is segmented into multiple cells with different NP ratios. Second cells with NP ≥ 1 provide safety assurance, while first cells with NP < 1 control the overall cost. This segmentation enables the system to achieve safety improvement without proportionally increasing cost across the entire battery.
Solution Approach 2:
The NP ratio parameter is varied across different cells rather than being uniform throughout the battery. This parameter change strategy allows optimization of safety performance in critical cells while maintaining cost-effectiveness in other cells, achieving a balanced solution.
3Ease of manufacture
If a single-cell design with NP < 1 is used to reduce cost, then manufacturing cost is reduced, but the cell is prone to overcharging when SOC approaches saturation level, posing safety risks
Solution Approach 1:
Cells with NP ≥ 1 act as intermediary safety components in the battery system. These second cells serve as a protective mechanism that prevents overcharging of the system, while allowing the use of cost-effective NP < 1 cells for the majority of the battery capacity.
Solution Approach 2:
The battery system incorporates cells with NP ≥ 1 as a preemptive safety measure before overcharging can occur. These cells provide a buffer or cushion against overcharge conditions, allowing the system to use cheaper NP < 1 cells while maintaining overall safety.
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 enhances safety performance and prolongs the cycle life of the battery by limiting voltage changes and forming a stable SEI film within a low voltage range, ensuring capacity and thermal stability.
Implementation Method 1
NPA1 is a ratio of a first lithium intercalation specific capacity of the negative electrode plate to a first lithium deintercalation specific capacity of the positive electrode plate
Implementation Method 2
NPA1 is a ratio of a first lithium intercalation specific capacity of the negative electrode plate to a first lithium deintercalation specific capacity of the positive electrode plate
Data Source
AI summary
A cell combination, a battery, and an electric apparatus. The cell combination comprises first cells and second cells, wherein the number of first cells is greater than or equal to the number of second cells, and each of the first cells and the second cells comprises a positive electrode sheet and a negative electrode sheet; the cell combination satisfies: 0.7≤NPA1≤1.05 NPB1 and NPA1<1, or 0.75≤NPA2≤1.05 NPB2 and NPA2<1.2; and when the state of charge of a single-cell battery comprising a second cell is in the range of 95% to 100%, each time the state of charge of the single-cell battery is changed by 1%, a voltage change of the second cell is correspondingly greater than 5 mV.