Phosphate Electrolyte Composition for Stable Lithium-Metal Cycling
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Solution Overview
Problem
The incompatibility between phosphate-based electrolytes and lithium metal in lithium-metal batteries leads to poor cycle life and stability, along with safety hazards due to high reactivity and dendrite formation.
Innovation Solution
A phosphate-based non-flammable electrolyte system using dimethyl (2-methoxyethoxy)methylphosphonate or diethyl (2-methoxyethoxy)methylphosphonate as the main solvent, combined with a fluorine-containing lithium salt and a local high concentration, which inhibits lithium dendrite growth and improves compatibility with the lithium metal anode.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If phosphate solvent is used as flame-retardant electrolyte, then safety is improved through non-flammability and free radical capture mechanism, but compatibility with lithium metal deteriorates leading to poor cycle life and dendrite formation
Solution Approach 1:
The patent changes the concentration parameter of phosphate solvent from traditional low concentration (5-20%) to local high concentration (60-90%) near the lithium metal surface. This parameter change transforms the electrolyte's behavior: at local high concentration, phosphate forms a stable protective interface layer that prevents dendrite growth while maintaining flame-retardant properties. The transition from low to high concentration resolves the contradiction between safety and cycle life.
Solution Approach 2:
The patent creates a local high concentration zone of phosphate solvent specifically at the lithium metal surface, rather than uniformly distributing it throughout the electrolyte. This local quality approach allows the phosphate to form a protective interface layer where it is most needed (at the anode surface) while maintaining overall electrolyte functionality. The local concentration gradient resolves the contradiction by providing flame-retardant protection and dendrite suppression at the critical interface without compromising bulk electrolyte performance.
2Reliability
If traditional carbonate-based electrolyte is used, then compatibility with lithium metal is improved, but safety deteriorates due to high reactivity, side reactions, and dendrite formation
Solution Approach 1:
The patent creates a composite electrolyte system combining phosphate solvent (for safety and stability) with lithium salt (for ionic conductivity). This composite approach integrates the beneficial properties of both components: phosphate provides flame-retardant capability and interface stability, while lithium salt ensures adequate conductivity. The composite electrolyte resolves the contradiction between interface stability and safety by synergistically combining materials with complementary functions.
Solution Approach 2:
The patent converts the traditionally harmful high reactivity of phosphate with lithium metal into a beneficial protective interface layer. By using local high concentration, the phosphate's reactivity is directed toward forming a stable solid electrolyte interphase (SEI) that prevents further unwanted reactions and dendrite growth. The harmful reactivity is thus transformed into a protective mechanism that simultaneously improves interface stability and safety.
3Reliability
If film-forming additive is used to improve phosphate compatibility, then cycle life is improved, but battery performance deteriorates and dosage control becomes difficult
Solution Approach 1:
The patent extracts the film-forming function from separate additive components and integrates it directly into the phosphate solvent itself by using local high concentration. Instead of adding trace amounts of film-forming additives (which cause performance degradation), the phosphate at 60-90% local concentration performs the film-forming function inherently. This extraction of the film-forming role from additives to the main solvent resolves the contradiction between cycle stability and battery performance.
4Reliability
If electrolyte system with local high concentration is used, then irreversible decomposition of phosphate is inhibited and reversible electrochemical cycle is achieved, but most phosphate molecules are complexed with Lit leaving no free solvent molecules
Solution Approach 1:
The patent applies preliminary action by forming a stable protective interface layer of phosphate complex before irreversible decomposition can occur. The local high concentration ensures that phosphate molecules are pre-organized at the lithium surface to create a stable SEI layer, preventing subsequent decomposition reactions. This preliminary protective layer formation resolves the contradiction by enabling reversible cycling while managing the complexation of phosphate molecules.
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 proposed electrolyte system significantly enhances the coulombic efficiency and cycle life of lithium-metal batteries, while also improving safety by preventing dendrite growth and reducing reactivity with the lithium metal.
Implementation Method 1
Free radical capture mechanism of phosphate is that: when the temperature rises, the phosphate is gasified by heating to release phosphorus-containing free radicals, and the phosphorus-containing free radicals capture hydrogen free radicals and hydroxyl free radicals in the system, thus preventing combustion.
Implementation Method 2
When the electrolyte system with the local high concentration is used, most phosphate solvent molecules are complexed with Lit, and almost none of free solvent molecules exist.
Data Source
AI summary
The invention belongs to the technical field of batteries, and discloses a phosphate-based flame-retardant electrolyte and a lithium-metal battery, and the phosphate-based flame-retardant electrolyte consists of a lithium salt, a phosphate solvent and a diluent. According to the invention, dimethyl (2-methoxyethoxy)methylphosphonate or diethyl (2-methoxyethoxy)methylphosphonate is used as a novel phosphate solvent, an electrolyte system with local high salt concentration is adopted, most phosphate solvent molecules are complexed with Li+ at the local high salt concentration by adjusting dosages of the lithium salt, the phosphate solvent and the diluent, so almost none of free solvent molecules exist, thus inhibiting irreversible decomposition of phosphate molecules on a surface of a li-anode, and meanwhile, the flame retardancy of the phosphate solvent greatly improves the safety of the lithium-metal battery.