Fluorinated Disordered Rocksalt Cathodes for Higher F Solubility

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Solution Overview

Problem

Lithium-rich cation-disordered rocksalt oxide cathodes face limitations in achieving high fluorine substitution due to thermodynamic driving force limitations and phase segregation issues, which impede the improvement of their electrochemical performance.

Innovation Solution

The use of a fluorinated polymeric precursor, such as polytetrafluoroethylene (PTFE), to increase fluorine solubility in lithium-rich cation-disordered rocksalt cathodes, allowing for higher fluorine content up to 10-12.5 at.% and improving electrochemical performance by enhancing transition-metal redox contributions while reducing oxygen redox irreversibility.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Quantity of substance

If LiF precursor is introduced during solid-state synthesis to achieve fluorine substitution, then fluorine content increases, but phase segregation occurs beyond 7.5 at.% F content

Engineering Contradiction:

Improvefluorine contentVSAvoidphase segregation

Core Design Contradiction:

Quantity of substanceVSStability of the object's composition

Solution Approach 1:

The patent changes the fluorine precursor from LiF to ammonium bifluoride (NH4HF2), which fundamentally alters the fluorine delivery mechanism and solubility characteristics, enabling higher fluorine content (up to 12.5 at.%) without phase segregation. This parameter change in precursor chemistry resolves the contradiction by providing a different thermodynamic pathway for fluorine incorporation.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent introduces ammonium bifluoride as an intermediary substance that mediates fluorine incorporation into the DRX structure. The NH4HF2 precursor decomposes to provide fluorine in a controlled manner, acting as an intermediary that prevents direct LiF phase segregation while achieving high fluorine substitution levels.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Quantity of substance

If higher fluorine substitution is achieved through prolonged high-energy ball-milling, then fluorine content increases, but manufacturing complexity and difficulty of commercial scale-up increase

Engineering Contradiction:

Improvefluorine contentVSAvoidmanufacturing scalability

Core Design Contradiction:

Quantity of substanceVSEase of manufacture

Solution Approach 1:

The patent replaces the mechanical ball-milling system with a thermal processing system using ammonium bifluoride precursor. Instead of relying on prolonged mechanical energy input to achieve fluorine substitution, the invention uses thermal decomposition of NH4HF2 during synthesis, which is easier to scale up commercially and provides more consistent fluorine incorporation.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

3Reliability

If fluorine substitution is increased to improve electrochemical performance, then oxygen redox reversibility improves, but achieving higher F content is limited by thermodynamic driving force

Engineering Contradiction:

Improveoxygen redox reversibilityVSAvoidfluorine solubility

Core Design Contradiction:

ReliabilityVSQuantity of substance

Solution Approach 1:

The patent changes the thermodynamic parameters of fluorine incorporation by using ammonium bifluoride instead of LiF. This precursor change provides a different thermodynamic driving force that overcomes the limited fluorine solubility in DRX structures, enabling higher fluorine content (10-12.5 at.%) while maintaining oxygen redox reversibility improvements.

Inventive Principle:

Principle #35Parameter changes

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 results in a significant increase in reversible discharge capacity and capacity retention, with a 40% increase in capacity retention after 30 cycles, demonstrating improved electrochemical stability and performance of the cathode materials.

Implementation Method 1

The use of a fluorinated polymeric precursor, such as polytetrafluoroethylene (PTFE), to increase fluorine solubility in lithium-rich cation-disordered rocksalt cathodes

Methodology Applied

Scientific EffectThermal decomposition: Pyrolysis

Implementation Method 2

The large charge storage capacity in the DRX materials is attributed to the collective redox activities from a single- or multi-electron pairs of TM cations, such as Ni2+/Ni3+, Ni2+/Ni4+, Mn2+/Mn4+, Mn3+/Mn4+

Methodology Applied

Scientific EffectRedox reactions: Redox Reactions

Data Source

PatentUS11884552B2Fluorinated cation-disordered rocksalt materials and methods of making thereof

Publication Date: 2024.01.30 RGT UNIV OF CALIFORNIA

AI summary

This disclosure provides systems, methods, and apparatus related to lithium metal oxyfluorides. In one aspect, a method for manufacturing a lithium metal oxyfluoride having a general formula Li1+x(MM′)zO2-yFy, with 0.6≤z≤0.95, 0<y≤0.67, and 0.05≤x≤0.4, the lithium metal oxyfluoride having a cation-disordered rocksalt structure, includes: providing at least one lithium-based precursor; providing at least one redox-active transition metal-based precursor; providing at least one redox-inactive transition metal-based precursor; providing at least one fluorine-based precursor comprising a fluoropolymer; and mixing the at least one lithium-based precursor, the at least one redox-active transition metal-based precursor, the at least redox-inactive transition metal-based precursor, and the at least one fluorine-based precursor comprising a fluoropolymer to form a mixture.