Laminated Battery Separator for Shutdown and Thermal Stability
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Solution Overview
Problem
Current lithium secondary batteries face safety concerns due to thermal runaway and internal short circuits, particularly when the separator's shutdown mechanism is activated, as the separator's material properties lead to increased internal resistance and potential for dendrite growth, and manufacturing issues arise from uneven friction coefficients during electrode winding.
Innovation Solution
An electrochemical device with a separator comprising a first porous layer of thermoplastic resin and a second porous layer of heat-resistant insulating particles, where the first layer ensures shutdown by melting and filling pores, and the second layer prevents short circuits by maintaining structural integrity at high temperatures, and the manufacturing method involves wrapping the separator around a winding shaft with the lower friction side facing the shaft to facilitate easy removal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a polyethylene separator with low melting point is used to achieve shutdown function, then safety against short circuit is improved, but the separator shrinks at high temperatures causing internal short circuit
Solution Approach 1:
The separator is divided into multiple functional layers: a polyethylene microporous film layer for shutdown function and a heat-resistant porous layer containing inorganic oxide particles for dimensional stability. Each layer performs its specific function independently, resolving the contradiction between shutdown capability and thermal stability.
Solution Approach 2:
The separator uses a composite structure combining organic polyethylene resin with inorganic oxide particles (alumina, silica, etc.). This composite material integrates the low melting point advantage of polyethylene for shutdown with the high temperature stability of inorganic oxides, preventing shrinkage at elevated temperatures.
2Strength
If the separator is drawn to ensure strength during manufacturing, then mechanical strength is improved, but the shutdown temperature increases close to thermal runaway temperature
Solution Approach 1:
The separator structure separates the strength-providing function from the shutdown function. The heat-resistant porous layer with inorganic oxide particles provides mechanical strength without affecting the shutdown temperature, while the polyethylene layer maintains its original low shutdown temperature despite minimal drawing.
3Stability of the object's composition
If a heat-resistant resin layer is added to prevent thermal shrinkage, then dimensional stability is improved, but the separator structure becomes more complex
Solution Approach 1:
The heat-resistant porous layer is formed with controlled porosity (30-70%) using inorganic oxide particles, allowing ion permeability while providing thermal stability. The porous structure maintains electrolyte contact and ion transport pathways, reducing the impact of added complexity on battery performance.
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
The solution enhances safety by preventing thermal runaway and internal short circuits, while improving manufacturing productivity by reducing winding displacement and ensuring effective shutdown functionality, thus ensuring reliable operation at high temperatures.
Implementation Method 1
the resin constituting the separator is melted at a temperature not more than the thermal runaway (abnormal heat generation) temperature of the battery and the pores of the separator are closed by melting the resin
Implementation Method 2
a second separator layer composed of a heat-resistant resin, an inorganic oxide, or the like has been proposed
Data Source
AI summary
An electrochemical device of the present invention includes a positive electrode, a negative electrode, a non-aqueous electrolyte, and a separator. The separator includes a first porous layer composed mainly of a thermoplastic resin and a second porous layer composed mainly of insulating particles with a heat resistant temperature of 150° C. or higher. The first porous layer is disposed to face the negative electrode.