Lithium Metal Protective Layer via Composite Graft Copolymer
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Solution Overview
Problem
Lithium secondary batteries using lithium metal negative electrodes face limitations due to dendrite formation, low safety, and poor performance caused by decomposition of liquid electrolytes and instability at the electrode interface, leading to short circuits and fires.
Innovation Solution
A protective layer composed of a poly(arylene ether sulfone)-poly(ethylene glycol) graft copolymer is synthesized and applied to the lithium metal surface, enhancing mechanical strength, thermal stability, and ion conductivity, thereby inhibiting dendrite growth and improving battery safety and performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If conventional protective layer materials (PVDF, PMMA, PDMS, PTFE) are used to protect lithium metal negative electrode, then mechanical protection is provided, but high resistance and low ion conductivity degrade battery performance
Solution Approach 1:
The patent uses a composite protective layer made of PVDF-HFP copolymer and inorganic particles (LiF, Li2SiO3, or Li2SiO2). The PVDF-HFP copolymer provides mechanical strength and flexibility, while the inorganic particles fill voids and improve ion conductivity. This composite structure resolves the contradiction by combining materials with complementary properties to achieve both protection and performance.
Solution Approach 2:
The patent modifies the chemical structure of PVDF by copolymerizing it with HFP (hexafluoropropylene) to create PVDF-HFP copolymer. This parameter change in polymer composition improves the material's ion conductivity and electrochemical stability while maintaining mechanical properties, thereby resolving the performance degradation issue.
2Strength
If conventional protective layer materials are used to protect lithium metal negative electrode, then some protection is achieved, but very low chemical stability at the interface between protective layer and electrolyte occurs
Solution Approach 1:
The protective layer combines PVDF-HFP copolymer with inorganic particles (LiF, Li2SiO3, or Li2SiO2). The inorganic particles form a stable interface with the electrolyte, preventing decomposition reactions that would occur with conventional organic-only materials. This composite approach achieves both protection and chemical stability.
Solution Approach 2:
The inorganic particles act as sacrificial components that form stable surface films during initial cycles, protecting the underlying PVDF-HFP copolymer from electrolyte decomposition. These particles are consumed or transformed to create a stable interface, ensuring long-term chemical stability.
3Strength
If conventional protective layer materials are used to protect lithium metal negative electrode, then mechanical barrier is formed, but low ion conductivity results
Solution Approach 1:
The inorganic particles (LiF, Li2SiO3, or Li2SiO2) create a porous or interconnected structure within the PVDF-HFP copolymer matrix. This porous structure provides pathways for lithium ion transport while the PVDF-HFP copolymer matrix maintains mechanical integrity. The result is a protective layer that is both mechanically strong and ion-conductive.
Solution Approach 2:
The composite of PVDF-HFP copolymer and inorganic particles creates a synergistic effect where the polymer provides mechanical strength and the inorganic particles provide ion conductivity pathways. This resolves the contradiction between barrier function and ion transport.
4Quantity of substance
If lithium metal is used as negative electrode to achieve high energy density, then specific capacity and weight advantage are obtained, but decomposition of liquid electrolytes and dendrite formation occur
Solution Approach 1:
The PVDF-HFP copolymer/inorganic particle composite protective layer acts as an intermediary between the lithium metal and the liquid electrolyte. It prevents direct contact and harmful reactions while allowing lithium ion transport. This intermediary layer suppresses electrolyte decomposition and dendrite formation, enabling safe use of high-capacity lithium metal electrodes.
Solution Approach 2:
The protective layer is applied preliminarily to the lithium metal surface before battery operation. It pre-forms a stable interface that prevents subsequent electrolyte decomposition and dendrite growth during cycling, ensuring long-term safety and stability of the high-energy-density lithium metal electrode.
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 protective layer effectively suppresses lithium dendrite formation, ensures long-term safety, and enhances the performance of lithium secondary batteries by maintaining high mechanical strength and ion conductivity, reducing resistance and improving battery stability.
Implementation Method 1
A protective layer composed of a poly(arylene ether sulfone)-poly(ethylene glycol) graft copolymer is synthesized and applied to the lithium metal surface
Implementation Method 2
enhancing mechanical strength, thermal stability, and ion conductivity, thereby inhibiting dendrite growth
Data Source
AI summary
Disclosed is a protective layer to protect a lithium metal negative electrode for a lithium secondary battery, in which the protective layer may inhibit formation of lithium dendrite and improve thermal/chemical stability, and conductivity of lithium ions. Further, disclosed are a production method of the protective layer, and a lithium secondary battery including the protectively layer. The protective layer contains a poly(arylene ether sulfone)-poly(ethylene glycol) graft copolymer represented by a following Chemical Formula 1:where, in the Chemical Formula 1, n is an integer of 60 to 80, and m is an integer of 40 to 45.