Inorganic Battery Electrolytes for Stable SEI and Low Flammability
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Solution Overview
Problem
Lithium ion batteries face issues with the flammability, volatility, and thermal instability of organic electrolytes, leading to cell degradation and safety concerns, particularly due to the formation of lithium dendrites and unstable solid electrolyte interphases (SEI) in lithium metal anodes.
Innovation Solution
An all-inorganic electrolyte system comprising a mixture of phosphoranimine (PA) and phosphazene (Pz) derivatives, with optional monomeric phosphorus (MP) compounds, is used to reduce or eliminate organic components, forming a stable SEI rich in phosphorus-nitrogen compounds that enhances safety and performance by controlling volatility, flammability, and thermal stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If organic electrolyte solvents (ethylene carbonate, ethyl methyl carbonate) are used in lithium ion batteries, then the electrolyte provides good solubility for lithium salts and acceptable charge carrier transport, but the electrolyte becomes highly flammable and volatile with flash points as low as 30°C or less
Solution Approach 1:
The patent changes the chemical composition parameters of the electrolyte by replacing organic carbonate solvents with inorganic phosphazene solvents containing P=N bonds. This fundamental parameter change transforms the electrolyte from flammable organic compounds to non-flammable inorganic compounds, while maintaining adequate lithium salt solubility and charge carrier transport properties through the unique chemical structure of phosphazenes
Solution Approach 2:
The patent employs sacrificial phosphazene additives that form stable SEI layers on electrode surfaces. These additives are consumed during initial cycling to create protective interfaces, preventing subsequent decomposition of the main electrolyte. This sacrificial mechanism eliminates the need for continuous electrolyte replacement due to degradation, effectively making the electrolyte system durable despite the consumable nature of certain components
2Productivity
If organic electrolyte solvents are used to achieve high current density through good solubility, then charge carrier transport is sufficient, but the electrolyte degrades under current draw and high temperature causing cell rupture
Solution Approach 1:
The patent changes the thermal stability parameter by substituting organic solvents with inorganic phosphazene solvents. The P=N bond structure and inorganic nature of phosphazenes provide inherent thermal stability that prevents decomposition at elevated temperatures, allowing the battery to operate at high current densities without electrolyte degradation or cell rupture
Solution Approach 2:
The patent implements preliminary formation of stable SEI layers through initial cycling or pre-treatment steps. This preliminary action creates protective interfaces on electrode surfaces before high current operation begins, preventing subsequent electrolyte decomposition and enabling sustained high current density operation with improved reliability
3Device complexity
If conventional organic electrolytes are used, then the electrolyte system is simple and well-established, but lithium dendrites form and SEI layers are unstable leading to catastrophic failure
Solution Approach 1:
The patent changes the chemical composition parameter from organic to inorganic phosphazene solvents, which fundamentally alters SEI formation and stability characteristics. The inorganic phosphazene molecules form more stable and conductive SEI layers that prevent lithium dendrite formation, improving reliability without significantly increasing system complexity
Solution Approach 2:
The patent creates composite electrolyte systems combining phosphazene solvents with lithium salts and potentially other additives. This composite approach leverages the beneficial properties of each component: phosphazenes provide thermal stability and SEI formation, lithium salts provide charge carriers, and the combination achieves both stability and functionality
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 PA/Pz solvent system improves the stability and safety of lithium ion batteries by forming a protective SEI that prevents bulk electrolyte degradation, allowing efficient charge carrier transport while reducing the risk of catastrophic failures and enhancing high-energy electrode compatibility.
Implementation Method 1
the electrolyte should be chemically inert with respect to the battery chemistry, with the exception of the formation of a stable solid electrolyte interphase (SEI) layer near the reactive surface of the electrode
Implementation Method 2
A considerable limitation of lithium ion batteries containing lithium salts in organic solvents
Implementation Method 3
permits flow of the charge carrier ions between the bulk electrolyte solution and the electrode surfaces
Implementation Method 4
solubility for a supporting salt which yields a charge carrier ion in sufficient concentration to permit high current density
Data Source
AI summary
An all-inorganic electrolyte formulation for use in a lithium ion battery system comprising at least one of each a phosphoranimine, a phosphazene, a monomeric organophosphate and a supporting lithium salt. The electrolyte preferably has a melting point below 0° C., and a vapor pressure of combustible components at 60.6° C. sufficiently low to not produce a combustible mixture in air, e.g., less than 40 mmHg at 30° C. A solid electrolyte interface layer formed by the electrolyte with an electrode is preferably thermally stable ≥80° C.