Wound Lithium Secondary Battery Layout for Negative Electrode Durability
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Solution Overview
Problem
Lithium secondary batteries with metal foil negative electrodes often suffer damage during repeated charge and discharge due to the expansion and contraction of the negative electrode.
Innovation Solution
A lithium secondary battery design featuring a wound electrode group with a negative electrode current collector larger than the positive electrode mixture layer, where the positive and negative electrodes are arranged such that their center lines are not on the same straight line, and the negative electrode lead is connected to a non-facing region of the negative electrode current collector.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If a foil of metal other than lithium metal is used to form a negative electrode, then the battery structure is stable, but the negative electrode is damaged during repeated charge and discharge
Solution Approach 1:
The patent applies asymmetry by making the negative electrode current collector larger in area than the positive electrode mixture layer, and positioning their center lines at different locations. This asymmetric design creates a non-uniform stress distribution during charge-discharge cycles, preventing concentrated stress at the center and reducing damage to the negative electrode structure.
Solution Approach 2:
The patent extends the negative electrode current collector beyond the boundaries of the positive electrode mixture layer in the planar dimension. This dimensional extension allows the negative electrode to accommodate volume changes during lithium deposition and dissolution without generating excessive mechanical stress, thereby improving durability while maintaining structural stability.
2Reliability
If the negative electrode current collector is made larger than the positive electrode mixture layer, then stress is distributed asymmetrically, but the electrode group complexity increases
Solution Approach 1:
The asymmetric configuration of the negative electrode current collector extending beyond the positive electrode mixture layer creates favorable stress distribution during operation. While this increases geometric complexity, it significantly improves negative electrode durability by preventing stress concentration and structural damage during repeated charge-discharge cycles.
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 design effectively suppresses damage to the negative electrode by distributing the stress of expansion asymmetrically and reducing the likelihood of cracks, thereby enhancing the battery's durability and performance.
Implementation Method 1
In the lithium secondary battery, lithium metal deposits on the negative electrode during charge, and the deposited lithium metal dissolves in the electrolyte during discharge.
Implementation Method 2
a non-aqueous electrolyte, the wound electrode group including: a positive electrode, a negative electrode
Data Source
AI summary
A lithium secondary battery with a positive electrode active material including a composite oxide containing lithium and a transition metal. A molar ratio: MLi/MTM of a total lithium amount per unit area MLi in a positive electrode and a negative electrode to a transition metal amount per unit area MTM in the positive electrode is 1.1 or less. The negative electrode includes a negative electrode current collector larger in area than the positive electrode mixture layer. In the wound electrode group in an unwound state, center lines dividing the positive electrode mixture layer and the negative electrode current collector along their winding direction into two halves are not on the same straight line. The negative electrode lead is connected at its one end to a non-facing region not facing the positive electrode mixture layer of the negative electrode current collector.