Phosphate Triester Electrolytes for Thermally Stable Lithium-Ion Cycling
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Solution Overview
Problem
Batteries that cycle lithium ions face issues with thermal and electrochemical stability, particularly at elevated temperatures, leading to gasification, swelling, and reduced capacity retention due to the use of low-boiling-point solvents like ethers and organic carbonates.
Innovation Solution
Formulating electrolytes with phosphate triester solvents having high boiling points and high LiNO3 concentrations to stabilize the battery, promoting the formation of stable solid electrolyte interphases and preventing gasification, while using a mixture of solvents to enhance ion conductivity and electrochemical performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If low-boiling-point solvents like ethers and organic carbonates are used in electrolytes, then ion conductivity and electrochemical performance are improved, but thermal stability deteriorates leading to gasification and swelling at elevated temperatures
Solution Approach 1:
The patent changes the boiling point parameter of the electrolyte solvent from low (ethers and organic carbonates) to high (phosphate triesters with boiling points ≥150°C). This parameter change resolves the contradiction by maintaining thermal stability and preventing gasification while the patent ensures ion conductivity is maintained through the specific molecular structure of the phosphate triester and optimal LiNO3 concentration (0.5-4.0 M).
Solution Approach 2:
The patent creates a composite electrolyte system combining phosphate triester solvents with lithium nitrate salts. This composite material approach allows the electrolyte to simultaneously achieve high thermal stability (preventing gasification) and good ion conductivity, resolving the contradiction between thermal stability and harmful gas generation at elevated temperatures.
2Reliability
If high concentrations of lithium nitrate are used in the electrolyte, then thermal stability and SEI formation are improved, but viscosity increases reducing ion mobility
Solution Approach 1:
The patent optimizes the lithium nitrate concentration parameter within the range of 0.5-4.0 M to achieve the desired balance. At these concentrations, the phosphate triester electrolyte forms stable SEI layers improving electrochemical stability while maintaining sufficient ion mobility for battery operation.
3Temperature
If phosphate triester solvents with high boiling points are used, then thermal stability is improved, but manufacturing complexity increases due to purification requirements
Solution Approach 1:
The patent specifies a boiling point parameter of ≥150°C for the phosphate triester solvent to ensure thermal stability and prevent gasification. This parameter change improves thermal performance while the patent addresses manufacturing considerations through the inherent stability of the phosphate triester structure that reduces degradation and purification complexity.
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 electrolytes improve thermal stability, inhibit gasification, and enhance cycling stability and capacity retention by forming uniform SEI layers, reducing dendrite formation, and maintaining efficient lithium ion conduction.
Implementation Method 1
The electrolyte comprises an organic solvent and a lithium salt in the organic solvent. The organic solvent comprises a primary solvent component and a secondary solvent component. The primary solvent component comprising a phosphate triester... The lithium salt comprises lithium nitrate (LiNO3).
Implementation Method 2
an ionically conductive electrolyte that provides a medium for the conduction of lithium ions between the positive and negative electrodes during discharge and charge of the batteries
Implementation Method 3
ability to form stable ionically conductive solid electrolyte interphases on surfaces of the positive electrode and/or the negative electrode... promoting the formation of stable solid electrolyte interphases
Data Source
AI summary
An electrolyte for a battery that cycles lithium ions includes an organic solvent and a lithium salt in the organic solvent. The organic solvent includes a primary solvent component and a secondary solvent component. The primary solvent component includes a phosphate triester having the formula R1O—P(═O)(OR2)(OR3), wherein R1, R2, and R3 are each individually a fluorinated or nonfluorinated organic group selected from the group consisting of hydrocarbyl, heterohydrocarbyl, silyl, siloxy, alkoxysilyl, cyano, and alkylcyano. The lithium salt includes lithium nitrate (LiNO3). The lithium nitrate is present in the organic solvent at a concentration of greater than or equal to 0.5 moles per liter and less than or equal to 4 moles per liter. The electrolyte is configured to provide a medium for the conduction of lithium ions between a negative electrode including a lithium-based electroactive negative electrode material and a positive electrode including an olivine-type lithium transition metal oxide.