Wound Battery Separator Coating for Bent-Section Swelling Gaps
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Solution Overview
Problem
Lithium ion batteries experience reduced charge-discharge performance and energy density at low temperatures due to electrolyte transmission barriers caused by negative electrode swelling, leading to insufficient lithium intercalation and separation, especially in bent portions of the battery.
Innovation Solution
A secondary battery design with a separator having a first and second coating on opposite surfaces, where the distance between positive and negative electrodes in the bent and straight portions is optimized (1<d1/d2<10), using polymers like polyvinylidene fluoride and copolymers with additives to create an ideal gap for swelling while maintaining adhesive force and energy density.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the gap between positive and negative electrodes is increased to reserve space for negative electrode swelling, then electrolyte transmission is improved, but battery thickness increases and volume energy density decreases
Solution Approach 1:
The separator is designed with non-uniform thickness: the first thickness in the bent portion is greater than the second thickness in the straight portion. This local differentiation allows the bent portion (where swelling and electrolyte transmission issues occur) to have extra space, while the straight portion maintains compact dimensions for high energy density.
Solution Approach 2:
The separator is divided into functionally distinct regions (bent portion with greater thickness and straight portion with lesser thickness), each optimized for its specific role. The bent portion handles swelling accommodation and electrolyte retention, while the straight portion focuses on space efficiency.
2Productivity
If the gap between positive and negative electrodes is increased to alleviate electrolyte transmission barrier, then charge-discharge performance is improved, but volume energy density is reduced
Solution Approach 1:
The separator thickness is locally optimized: greater thickness in the bent portion ensures adequate electrolyte transmission and swelling space where needed, while lesser thickness in the straight portion maximizes volume energy density. This selective thickness distribution resolves the contradiction between performance and density.
3Ease of manufacture
If uniform separator thickness is used, then manufacturing is simplified, but electrolyte transmission barrier occurs in bent portions due to negative electrode swelling
Solution Approach 1:
The separator employs non-uniform thickness with a first thickness in the bent portion and a second thickness in the straight portion. This design specifically addresses the electrolyte transmission barrier in bent portions by providing extra space for negative electrode swelling and electrolyte retention, while still being manufacturable through conventional processes.
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 alleviates electrolyte extrusion, maintains battery thickness, enhances adhesive force, and improves rate capability and cycle performance, reducing volume energy density loss and ensuring better lithium ion transmission.
Implementation Method 1
negative electrodes of most lithium ion batteries prepared by means of an existing battery technology swell continuously in the cycle process
Implementation Method 2
A first coating is disposed on the first surface of the substrate and includes a first polymer
Implementation Method 3
maintaining adhesive force and energy density
Implementation Method 4
ensuring better lithium ion transmission
Data Source
AI summary
A secondary battery, including a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode. The positive electrode, the separator, and the negative electrode are sequentially stacked and wound to form a winding structure including a bent portion and a straight portion. The separator includes a substrate, wherein the substrate has a first surface and a second surface opposite to the first surface. A first coating is disposed on the first surface of the substrate, and a second coating is disposed on the second surface of the substrate, wherein, in the bent portion of the winding structure, a first distance between adjacent positive and negative electrodes is d1, and in the straight portion of the winding structure, a second distance between the adjacent positive and negative electrodes is d2, wherein 1<d1/d2<10, and d1 and d2 are measured in a same unit.