Nonwoven Separator with Density Gradient for Battery Thermal Stability
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Solution Overview
Problem
Lithium ion secondary batteries face challenges in achieving high-temperature durability and high output due to issues with internal short-circuits, self-discharge, and low electron conductivity of materials like lithium iron phosphate, as well as the limitations of conventional separators such as polyolefin-based microporous polymer films which are prone to pinhole formation and thermal shrinkage.
Innovation Solution
A nonaqueous electrolyte secondary battery design featuring a positive electrode with olivine-structured Fe or Mn-containing phosphorus compounds, a negative electrode with titanium-containing metal oxides, and a nonwoven fabric separator with varying fiber density and porosity, bonded to the electrodes, enhancing lithium ion diffusion and thermal stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a polyolefin-based microporous polymer film is used as a separator, then the battery can be manufactured with conventional materials, but the separator is prone to pinhole formation and thermal shrinkage at high temperatures, causing internal short-circuits and self-discharge
Solution Approach 1:
The patent changes the material parameter of the separator from polyolefin-based microporous polymer film to nonwoven fabric made of heat-resistant fibers (polyester, polyamide, acrylic). This material substitution eliminates thermal shrinkage at high temperatures while maintaining porosity and ion permeability, directly resolving the contradiction between conventional manufacturability and high-temperature reliability
Solution Approach 2:
The patent creates a composite structure by bonding the nonwoven fabric separator to at least one electrode surface. This composite configuration enhances the overall thermal stability and mechanical strength of the battery assembly, preventing internal short-circuits while maintaining the functional properties of the separator
2Temperature
If lithium iron phosphate is used as a positive electrode active material, then thermal stability is improved, but electron conductivity is low, preventing high output performance
Solution Approach 1:
The patent modifies the electron conductivity parameter of lithium iron phosphate by coating its surface with conductive materials such as carbon or metal particles. This surface modification maintains the inherent thermal stability of lithium iron phosphate while dramatically improving electron conductivity, enabling high output performance without sacrificing thermal safety
Solution Approach 2:
The patent creates a composite positive electrode structure by combining lithium iron phosphate particles with conductive additives (carbon, metal particles) and binder materials. This composite approach synergistically combines the thermal stability of lithium iron phosphate with the high conductivity of carbon/metal materials, resolving the contradiction between thermal safety and power output
3Power
If the separator thickness is reduced, then the internal resistance is lowered, but pinholes are easily formed, causing internal short-circuits
Solution Approach 1:
The patent changes the structural parameters of the separator by using nonwoven fabric with optimized fiber arrangement, porosity (30-80%), and thickness (5-50 μm). The nonwoven fabric structure provides sufficient mechanical strength and pinhole resistance even at reduced thickness, while maintaining low ion transport resistance through controlled porosity
Solution Approach 2:
The patent creates a composite structure by bonding the nonwoven fabric separator to the electrode surface, which enhances the overall structural integrity. This bonding configuration allows the use of thinner separators without compromising reliability, as the electrode-separator composite provides additional mechanical support while maintaining low internal resistance
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 configuration reduces interfacial resistance, suppresses internal resistance increases, and achieves high-temperature durability and output characteristics, while maintaining low internal resistance and high porosity, even at temperatures above 80°C.
Implementation Method 1
charge/discharge is carried out through the movement of lithium ions between a positive electrode and a negative electrode
Implementation Method 2
a nonwoven fabric separator made of heat-resistant fibers... excellent in chemical and electrochemical stability, strength, and corrosion resistance
Implementation Method 3
a nonwoven fabric separator bonded to a surface of at least one of the positive electrode and the negative electrode
Data Source
AI summary
A nonaqueous electrolyte secondary battery of the present invention includes a positive electrode containing olivine-structured Fe or a Mn-containing phosphorus compound as a positive electrode active material; a negative electrode containing a titanium-containing metal oxide capable of inserting and extracting lithium ions as a negative electrode active material; a nonwoven fabric separator, which contains an electrically insulating fiber and is bonded to a surface of at least one of the positive electrode and the negative electrode; and a nonaqueous electrolyte. In a thickness direction of the nonwoven fabric separator, a density of the fiber on a side having contact with the positive electrode is high, and a density of the fiber on a side having contact with the negative electrode is low.