Oxidation-Resistant Separator for High-Voltage Li-Ion Batteries
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Solution Overview
Problem
Lithium ion secondary batteries face deterioration due to oxidation of the separator when the cut-off-voltage is set high, especially at elevated temperatures, limiting their energy density and lifespan.
Innovation Solution
A lithium ion secondary battery design featuring a separator with a polyolefin layer and an oxidation-resistant layer comprising a polymer without —CH2— and —CH(CH3)— groups, which faces the positive electrode, maintaining flexibility and preventing oxidation, while the polyolefin layer provides shutdown functionality at high temperatures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If the cut-off-voltage of charge is set high (4.3 V or more) to increase energy density, then the utilization rate of lithium in lithium cobalt oxide increases, but the separator deteriorates due to oxidation
Solution Approach 1:
The separator is divided into multiple functional layers: a polyethylene layer providing shutdown functionality and an oxidation-resistant layer (comprising polyimide, aramid, or polyamideimide) that protects against oxidation at high voltages. This segmentation allows each layer to perform its specific function independently, resolving the contradiction between high voltage operation and separator durability.
Solution Approach 2:
The separator uses a composite structure combining polyethylene (for shutdown function) with oxidation-resistant polymers (polyimide, aramid, or polyamideimide). This composite material approach enables the separator to simultaneously provide thermal safety through shutdown and chemical stability through oxidation resistance, allowing high voltage charging without degradation.
2Object-affected harmful factors
If polypropylene is used to resist oxidation at the positive electrode interface, then oxidization resistance improves, but oxidation still advances to deteriorate the battery at 4.3 V or more
Solution Approach 1:
The invention changes the chemical composition parameters of the oxidation-resistant layer by selecting polymers (polyimide, aramid, or polyamideimide) with higher oxidation potentials and superior thermal stability compared to polypropylene. This parameter change enables effective protection against oxidation even at high charging voltages of 4.3 V or more, preventing battery deterioration.
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 allows lithium ion secondary batteries to maintain performance and longevity even when charged to high voltages, enhancing energy density and extending battery life by preventing separator deterioration.
Implementation Method 1
the oxidation-resistant layer comprises an oxidation-resistant polymer; the main chain of the oxidation-resistant layer does not include a —CH2— group (methylene group) and does not include a —CH(CH3)— group (methylmethylene group)
Implementation Method 2
the polyolefin layer comprises polyethylene
Data Source
AI summary
A lithium ion secondary battery includes a positive electrode, a negative electrode, a non-aqueous electrolyte, and a separator interposed between the positive electrode and the negative electrode. The separator includes a polyolefin layer and an oxidation-resistant layer. The oxidation-resistant layer includes an oxidation-resistant polymer. A main chain of the oxidation-resistant polymer does not include a —CH2— group and a —CH(CH3)— group. The oxidation-resistant layer faces the positive electrode.