Low-Profile Li-Ion Electrode Roll for Uniform Current Density
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Solution Overview
Problem
Existing nonaqueous electrolyte rechargeable batteries, such as lithium-ion batteries, face issues with nonuniform current density distribution due to structural differences between flat and bent portions in the electrode body, leading to insufficient limitation of lithium metal deposition.
Innovation Solution
The method involves laminating positive and negative electrodes with a separator, rolling them into a low-profile form, and adjusting the air permeance of the separator in the bent and flat portions to equalize the combined resistance by controlling the air permeance and inter-electrode distance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If the electrode body is pressed to form a low-profile structure with flat and bent portions, then the cooling efficiency is improved and the electrode sheets are disposed closer to each other, but the nonuniformity of current density in the electrode body is not resolved and lithium deposition is not sufficiently limited
Solution Approach 1:
The invention applies different air permeance characteristics to different regions (flat portion vs. bent portions) of the separator. The separator is designed to have a first air permeance in the flat portion and a second air permeance in the bent portions, where the ratio between them is controlled within a specific range. This local differentiation compensates for the structural nonuniformity caused by low-profile pressing, ensuring uniform current density distribution and preventing lithium deposition while maintaining the cooling efficiency benefits of the compact structure.
2Reliability
If the packing density of bent portions is increased relative to flat portions, then the capacity maintenance rate is improved and lithium deposition is limited, but the structural nonuniformity between flat and bent portions causes various problems
Solution Approach 1:
The invention changes the physical parameter of air permeance in the separator to compensate for structural nonuniformity. By controlling the ratio of air permeance between bent portions and flat portion within a specific range, the invention achieves uniform current density distribution and high capacity maintenance rate without requiring uniform packing density throughout the electrode body. This parameter adjustment allows the battery to maintain both high reliability and structural stability.
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 approach effectively limits lithium metal deposition by ensuring uniform current density distribution, enhancing the battery's durability and performance by reducing nonuniformity in resistance.
Implementation Method 1
a porous resin separator disposed between the positive electrode and the negative electrode
Implementation Method 2
low-profile pressing the electrode body, which was rolled in the rolling, from a direction orthogonal to the roll axis to form a planar flat portion F and two semicircular rod-shaped bent portions R on opposite ends of the flat portion F, and restoring the electrode body from elastic deformation occurred in the low-profile pressing
Data Source
AI summary
A lithium-ion rechargeable battery includes an electrode body rolled about a roll axis to be low-profile. In a cross section orthogonal to the roll axis, the electrode body includes a planar flat portion pressed to have a low profile and two semicircular rod-shaped bent portions bent and formed on opposite ends of the flat portion. Combined resistance of reaction resistance caused by an inter-electrode distance with solution resistance caused by air permeance of the separator in site, longitudinally extending from center to a peripheral surface of each bent portion, equals combined resistance of the reaction resistance with the solution resistance in site, extending from straight line to a peripheral surface of the flat portion in a thickness-wise direction, to obtain uniform resistance of the electrode body, thereby limiting deposition of lithium metal caused by non-uniform current density.