Noncoated Edge Current Collector for Low Resistance Batteries
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Solution Overview
Problem
Nonaqueous electrolyte secondary batteries face challenges in achieving low internal resistance and excellent large current properties, particularly when subjected to fluctuating loads and environmental conditions, due to high internal resistance during charge-discharge at high currents.
Innovation Solution
The method involves producing a nonaqueous electrolyte secondary battery with a positive electrode and negative electrode, where the positive electrode current collector has a coated portion and a noncoated portion adjacent to its edge, with a controlled mass ratio and density of the active material layers, and tension processing is applied to the electrodes to optimize contact and reduce resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the internal resistance of the battery is reduced to enable large current discharge, then the large current property is improved, but the manufacturing precision of the electrode structure becomes more difficult to control
Solution Approach 1:
The patent applies local quality by creating a noncoated portion at the edge of the current collector that has different properties from the coated portion. This noncoated area allows for lead bonding without active material interference, enabling low-resistance electrical connections that reduce overall battery internal resistance and improve large current discharge capability.
Solution Approach 2:
The current collector is segmented into distinct coated and noncoated portions. The coated portion contains active material for electrochemical reactions, while the noncoated portion at the edge is dedicated for lead bonding. This segmentation allows optimization of each region's function, reducing contact resistance at the connection point without compromising the electrochemical performance of the active material area.
2Reliability
If the noncoated portion length is increased to improve lead bonding, then the electrical connection is improved, but the energy density of the battery is reduced
Solution Approach 1:
The patent optimizes the length parameter of the noncoated portion to a specific range (5-20 mm) based on the current collector width. This parameter optimization ensures sufficient area for reliable lead bonding and low-resistance electrical connection while minimizing the loss of active material area, thereby maintaining high energy density. The precise control of this dimensional parameter resolves the contradiction between connection quality and energy density.
Data Source
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AI summary
According to the embodiment, there is provided a nonaqueous electrolyte secondary battery comprising a positive electrode, a negative electrode, and a nonaqueous electrolyte. The positive electrode comprises a positive electrode current collector having a first surface and a first positive electrode active material layer provided on a part of the first surface. The positive electrode current collector comprises a coated portion on which the first positive electrode active material layer is provided and a noncoated portion which is adjacent to the coated portion in a direction parallel to the first surface, in which the first positive electrode active material layer is not present. The noncoated portion is adjacent to at least one edge of the positive electrode current collector and extends along the at least one edge. A length from a boundary between the coated portion and the noncoated portion to the at least one edge of the positive electrode current collector is within a range of 5 mm to 20 mm. A density of the first positive electrode active material layer is within a range of 3.1 g/cc to 3.4 g/cc. A ratio W1/W2 of a mass of the coated portion per unit area (W1) to a mass of the noncoated portion per unit area (W2) is from 0.997 to 1.