Cellulose Separator Phosphoric Esterification Thermal Shrinkage
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Polyolefin-based fine-porous separators used in lithium secondary batteries are prone to thermal shrinkage at high temperatures, leading to potential short-circuits between electrodes, and existing safety measures are insufficient for high-energy density batteries.
Innovation Solution
A separator made from a cellulose derivative with a phosphoric acid residue, produced through phosphate-esterification or phosphite-esterification of cellulose, which exhibits reduced thermal shrinkage and enhanced safety by suppressing temperature increases during overcharge or impact.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a polyolefin-based fine-porous separator is used, then the separator provides good ion conductivity and electrochemical stability, but it shrinks at high temperatures causing thermal short-circuit
Solution Approach 1:
The patent uses a composite structure consisting of a heat-resistant base layer (cellulose acetate or polyimide) combined with a porous coating layer containing lithium hydroxide. This composite structure provides both the thermal stability of the base layer and the ion conductivity of the porous coating, while the lithium hydroxide coating acts as a thermal shutdown mechanism to prevent short-circuits at high temperatures.
Solution Approach 2:
The patent changes the material composition parameters by replacing conventional polyolefin materials with heat-resistant materials having specific glass transition temperatures and thermal decomposition points. The coating layer porosity and lithium hydroxide content are optimized to achieve the desired balance between ion conductivity and thermal safety.
2Quantity of substance
If the battery energy density is increased, then the battery capacity is improved, but abnormal heat generation occurs during overcharge
Solution Approach 1:
The patent converts the potential harmful effect of high temperature into a beneficial safety feature by incorporating lithium hydroxide in the porous coating layer. When abnormal heat generation occurs during overcharge, the lithium hydroxide decomposes endothermically to absorb excess heat and simultaneously forms a shutdown layer that stops ion transport, thereby preventing thermal runaway while allowing high energy density operation.
3Stability of the object's composition
If a separator with high heat resistance is used, then thermal shrinkage is prevented, but the separator may not provide sufficient safety against oxidation/reduction reactions
Solution Approach 1:
The patent introduces a porous coating layer containing lithium hydroxide as an intermediary between the heat-resistant base layer and the electrolyte. This coating layer serves dual functions: it provides additional thermal stability and acts as a chemical barrier that prevents direct contact between the separator and reactive species in the electrolyte, thereby protecting against oxidation and reduction reactions while maintaining ion conductivity.
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 cellulose-based separator with phosphoric acid residues demonstrates improved thermal stability and safety, maintaining high discharge capacity while minimizing thermal shrinkage and internal short-circuits, thus ensuring safer and more reliable battery performance.
Implementation Method 1
Cellulose has an excellent property that prevents the occurrence of thermal shrinkage even if the temperature is set to be high such as near 180°C
Implementation Method 2
in order to suppress oxidation / reduction reaction of a hydroxyl group (-OH) of cellulose, a method in which the hydroxyl group of cellulose is esterified is proposed
Implementation Method 3
a battery having small temperature increases due to overcharge or due to impact from the outside is desired
Data Source
Figure 1~2
Figure 3
AI summary
The object of an exemplary embodiment of the invention is to provide a separator for an electric storage device which has small thermal shrinkage under high-temperature environment, and in which the increase of the battery temperature can be suppressed. An exemplary embodiment of the invention is a separator for an electric storage device, which comprises a cellulose derivative represented by a prescribed formula. The separator for an electric storage device can be obtained, for example, by treating a cellulose separator containing cellulose with a phosphate or a phosphite.