Block Copolymer Electrolytes for Lithium Battery Thermal Runaway Prevention
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Solution Overview
Problem
Rechargeable lithium batteries face challenges in combining high energy density with electrode stability due to dendrite growth and thermal runaway, which are exacerbated by the trade-off between ionic conductivity and mechanical properties in current polymer electrolytes.
Innovation Solution
Development of high elastic modulus, high ionic conductivity polymer electrolytes using linear block copolymers with a structural polymer block and a conductive polymer block, where the structural block forms a rigid framework for the conductive block to create nanostructured ionically conductive channels, and the incorporation of a lithium salt that precipitates at elevated temperatures to reduce conductivity and prevent thermal runaway.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If rubbery polymer electrolytes are used to achieve high ionic conductivity, then ionic conductivity is improved, but elastic modulus deteriorates (remains low at about 1 MPa)
Solution Approach 1:
The patent employs block copolymer electrolytes comprising a rigid glassy polymer block (polystyrene) and a flexible conductive polymer block (polyethylene oxide). This composite structure allows the glassy block to provide high elastic modulus (about 3 GPa) while the PEO block maintains ionic conductivity through segmental motion, thus resolving the contradiction between mechanical strength and ionic conductivity
Solution Approach 2:
The patent segments the polymer electrolyte into distinct functional blocks: a glassy polystyrene block for mechanical support and a flexible PEO block for ion transport. This segmentation allows each block to independently fulfill its specific function, enabling the overall material to achieve both high elastic modulus and adequate ionic conductivity
2Strength
If glassy polymer electrolytes are used to achieve high elastic modulus, then elastic modulus is improved (about 3 GPa), but ionic conductivity deteriorates (poor ion conductors)
Solution Approach 1:
The patent creates a composite block copolymer where the glassy polystyrene block provides the necessary high elastic modulus while the incorporated PEO block serves as the ion-conducting pathway, thus achieving both high mechanical strength and adequate ionic conductivity simultaneously
Solution Approach 2:
The patent applies local quality by confining the ion-conducting PEO segments to specific regions within the block copolymer structure, allowing these localized flexible regions to provide ionic conductivity while the overall glassy matrix maintains high elastic modulus
3Use of energy by moving object
If lithium salt is incorporated into polymer electrolyte to enhance ionic conductivity, then ionic conductivity is improved, but thermal stability deteriorates (thermal runaway occurs at elevated temperatures)
Solution Approach 1:
The patent incorporates a thermal shutdown additive that preemptively counteracts thermal runaway by decomposing at elevated temperatures to release gases that form an insulating barrier, thereby preventing the positive feedback loop between temperature increase and conductivity increase before thermal runaway can occur
Solution Approach 2:
The patent introduces a thermal shutdown additive as an intermediary substance that mediates between the lithium salt and the polymer matrix, absorbing excess heat and preventing direct thermal interaction that would lead to runaway, thus enhancing thermal stability while maintaining ionic 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 polymer electrolytes achieve high energy density and cycle life without dendrite growth and thermal runaway, with a conductivity drop at elevated temperatures providing a safety mechanism to prevent overheating in lithium batteries.
Implementation Method 1
the incorporation of a lithium salt that precipitates at elevated temperatures to reduce conductivity and prevent thermal runaway
Data Source
AI summary
A polymer that combines high ionic conductivity with the structural properties required for Li electrode stability is useful as a solid phase electrolyte for high energy density, high cycle life batteries that do not suffer from failures due to side reactions and dendrite growth on the Li electrodes, and other potential applications. The polymer electrolyte includes a linear block copolymer having a conductive linear polymer block with a molecular weight of at least 5000 Daltons, a structural linear polymer block with an elastic modulus in excess of 1×107 Pa and an ionic conductivity of at least 1×10−5 Scm−1. The electrolyte is made under dry conditions to achieve the noted characteristics. In another aspect, the electrolyte exhibits a conductivity drop when the temperature of electrolyte increases over a threshold temperature, thereby providing a shutoff mechanism for preventing thermal runaway in lithium battery cells.