Phosphorus-Nitrogen Solid Electrolytes for Low-Flammability Li Batteries
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Solution Overview
Problem
Conventional lithium-ion batteries face safety concerns due to the flammability and instability of organic electrolytes, leading to issues like lithium dendrite formation and internal short circuits, which limit their energy density and lifespan.
Innovation Solution
The use of phosphorus-nitrogen compounds as additives or co-solvents in electrolytes to reduce flammability, improve the formation of a stable solid electrolyte interphase (SEI), and enhance thermal stability, replacing organic solvents entirely to create a safer and more stable inorganic electrolyte system.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If organic electrolytes are used in lithium-ion batteries, then high current density and charge carrier transport are achieved, but flammability and thermal stability deteriorate
Solution Approach 1:
The patent changes the chemical composition parameters of the electrolyte by incorporating phosphorus-nitrogen compounds (such as phosphazenes and phosphoramidites) into the electrolyte system. These compounds modify the physical and chemical properties of the electrolyte, specifically reducing flammability while maintaining ionic conductivity through their unique molecular structure and interaction with lithium salts.
Solution Approach 2:
The patent creates a composite electrolyte system by combining phosphorus-nitrogen compounds with traditional carbonate solvents and lithium salts. This composite approach allows the electrolyte to benefit from both the high ionic conductivity of organic solvents and the thermal stability and flame resistance of phosphorus-nitrogen compounds, resolving the contradiction between productivity and safety.
2Object-affected harmful factors
If organic solvents are replaced with inorganic compounds, then flammability is reduced, but viscosity increases affecting charge carrier transport
Solution Approach 1:
The patent optimizes the molecular structure and concentration parameters of phosphorus-nitrogen compounds to achieve the right balance between viscosity and flame resistance. By selecting specific compounds with appropriate molecular weights and functional groups, and by controlling their concentration in the electrolyte (typically 5-50 wt%), the patent reduces viscosity while maintaining safety benefits.
Solution Approach 2:
The phosphorus-nitrogen compounds act as intermediary substances between fully organic electrolytes and purely inorganic alternatives. They provide the thermal stability and flame resistance of inorganic compounds while maintaining the fluidity and ionic conductivity characteristics of organic electrolytes, effectively mediating the trade-off between safety and transport efficiency.
3Reliability
If phosphorus-nitrogen compounds are added to electrolyte, then thermal stability and SEI formation improve, but device complexity increases
Solution Approach 1:
The phosphorus-nitrogen compounds perform multiple functions simultaneously: they act as flame retardants, SEI formers, and viscosity modifiers. This multi-functionality reduces the need for separate additives for each function, thereby simplifying the overall electrolyte formulation despite the introduction of new compounds. A single additive achieves what would traditionally require multiple components.
Solution Approach 2:
The patent utilizes the local chemical reactivity and structural properties of phosphorus-nitrogen compounds at the electrode-electrolyte interface to form stable SEI layers. The compounds concentrate their action at this critical interface region, providing localized protection and stability without requiring complex bulk electrolyte formulations. The SEI formation is a localized phenomenon that benefits from the specific chemical properties of phosphorus-nitrogen compounds at the interface.
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 approach significantly reduces the risk of thermal runaway and dendrite formation, enhancing the safety and energy density of lithium-ion batteries by stabilizing the electrolyte and improving lithium metal anode performance.
Implementation Method 1
the formation of a stable solid electrolyte interphase (SEI) layer near the reactive surface of the electrode, which permits flow of the charge carrier ions between the bulk electrolyte solution and the electrode surfaces, while protecting the bulk electrolyte solution from large-scale decomposition
Implementation Method 2
One approach to improve the safety performance of the electrolyte is to use additives and co-solvents to reduce the flammability of the organic carbonate and ester electrolytes
Implementation Method 3
A variety of additives and co-solvents have been proposed, including sulfones, ionic liquids, phosphates, phospholanes, phosphazenes (PZs), siloxanes, fluorinated carbonates, and fluorinated ethers and mixtures thereof. In addition to flammability suppression, additives have also been used to improve SEI formation, and to provide overcharge protection and thermal stability
Implementation Method 4
These electrolyte blends are highly volatile and highly flammable, with typical flash points as low as 30° C. or less. This presents serious safety concerns especially when utilized in large format cells or when the cells come under undue stress or physical damage
Data Source
AI summary
A solid electrolyte, comprising a solid polymer, ceramic, and/or polymer/ceramic composite materials and a phosphorus-containing plasticizer selected from the group consisting of a phosphazene and a phosphoranimine, which lacks hydroxyl and unstable phosphorus-halogen bonds, is electrochemically stable at a voltage of at least 3.5 V (vs. Li/Li+), and has a flash point of at least 100° C., wherein the solid electrolyte has a lithium ion conductivity of at least 1×10−6 S/cm.