Bilayer Polymer Electrolyte for Lithium Battery Dendrite Control
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Solution Overview
Problem
Lithium batteries face issues with mechanical strength and dendrite formation, leading to reduced lifetime, particularly due to the weak mechanical strength of polymer electrolyte films and the formation of lithium foams when using non-aqueous liquids.
Innovation Solution
A composite film electrolyte is developed, comprising two layers with a solvating polymer forming a continuous network and a nonsolvating polymer, which reduces lithium ion migration and prevents dendrite growth, enhancing mechanical strength and eliminating the need for excess lithium.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Duration of action of stationary object
If a polymer electrolyte film is used to suppress dendrite formation, then battery lifetime is improved, but mechanical strength is insufficient especially in operating temperature range
Solution Approach 1:
The patent uses a composite polymer electrolyte film comprising PEO and PVDF in a specific weight ratio range (PEO: 20-80 wt%, PVDF: 80-20 wt%). This composite structure combines the ion-conducting properties of PEO with the mechanical strength and thermal stability of PVDF, resolving the contradiction between suppressing dendrites and providing sufficient mechanical strength.
2Reliability
If nonaqueous liquid is used in conductive polymer to improve ion conductivity, then battery performance is enhanced, but lithium foam formation occurs which deactivates lithium
Solution Approach 1:
The patent completely eliminates nonaqueous liquids from the electrolyte composition, using only solid polymer materials (PEO and PVDF) with lithium salt. This extraction of the harmful liquid component prevents lithium foam formation while maintaining ion conductivity through the solid polymer matrix.
Solution Approach 2:
The patent replaces the liquid electrolyte system with a solid polymer electrolyte system, using inexpensive and stable polymer materials that do not form foams. This substitution eliminates the harmful side reactions associated with liquid electrolytes while providing sufficient ion transport capability.
3Quantity of substance
If excess lithium is used to compensate for deactivation by foam, then battery capacity is maintained, but battery complexity and cost increase
Solution Approach 1:
The patent converts the potential harm of liquid electrolyte foam formation into a benefit by completely eliminating the liquid component. The solid polymer electrolyte prevents foam formation from the outset, eliminating the need for excess lithium compensation and simplifying battery design.
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 composite film significantly increases the battery's lifetime by preventing dendrite formation and improving mechanical strength, with a 10-fold increase in cycle life compared to conventional batteries using a solid solution of lithium salt in PEO.
Implementation Method 1
a polymer material of the layer P contains a solvating polymer and a nonsolvating polymer... the solvating polymer forms a continuous network
Implementation Method 2
Lithium batteries operate by exchange of lithium ions between an anode and a cathode, through an electrolyte that comprises a lithium salt in solution
Data Source
AI summary
The invention relates to a bilayer polymer electrolyte for a lithium battery.The electrolyte comprises the layers N and P, each composed of a solid solution of an Li salt in a polymer material, the Li salt being the same in both layers, the polymer material content being at least 60% by weight, and the lithium salt content being from 5 to 25% by weight. The polymer material of the layer P contains a solvating polymer and a nonsolvating polymer, the weight ratio of the two polymers being such that the solvating polymer forms a continuous network. The polymer material of the layer N is composed of a solvating polymer and optionally a nonsolvating polymer, the weight ratio of the two polymers being such that the solvating polymer forms a continuous network, and the nonsolvating polymer does not form a continuous network.