Silicate Weakly Coordinating Anions for Stable Mg Electrolytes
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Solution Overview
Problem
Existing weakly-coordinating anions (WCAs) face challenges such as decomposition in the presence of highly electrophilic cations, limited redox stability, and synthetic reproducibility issues, which hinder their application in coordination chemistry and battery science.
Innovation Solution
Development of a new class of silicate anions with varied ligands and R1 groups, allowing for facile tuning of sterics and solubility, which are used as weakly coordinating anions in electrochemical cells.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional weakly-coordinating anions such as [PF6]−, [BF4]−, and [N(O3SCF3)]− are used, then redox stability is improved, but decomposition occurs in the presence of highly electrophilic cations
Solution Approach 1:
The patent employs composite anion structures combining borate cores with fluorinated alkoxide ligands (e.g., [B(O(CH(CF3)2)2]−, [Al(O(CH(CF3)2)2]−) to achieve both redox stability and resistance to electrophilic cations. The fluorinated groups provide electrochemical stability while the bulky alkoxide ligands prevent decomposition by highly electrophilic cations through steric protection.
Solution Approach 2:
The patent systematically varies parameters including the central atom (B, Al), ligand types (alkoxide, fluorinated groups), and substitution patterns to optimize both redox stability and electrophilic cation compatibility. This parameter tuning enables the anions to maintain stability across diverse electrochemical conditions.
2Reliability
If bulkier, less nucleophilic WCA-supported electrolytes are used, then ionic conductivity and stability are improved, but synthetic reproducibility becomes difficult
Solution Approach 1:
The patent optimizes the balance between bulkiness and synthetic tractability by carefully selecting ligand sizes and configurations. The fluorinated alkoxide ligands provide sufficient bulk for stability while maintaining synthetic reproducibility through well-defined structures that avoid the complexity issues of earlier bulky anions.
Solution Approach 2:
The patent applies bulk and electron-withdrawing characteristics locally at specific positions on the anion structure (fluorinated alkoxide ligands on the borate/aluminate core) rather than uniformly throughout, achieving the necessary stability and conductivity while maintaining synthetic feasibility.
3Reliability
If anions with highly-fluorinated and bulky alkoxide ligands are used, then support for reversible metal deposition and stripping is improved, but anodic stability is severely limited
Solution Approach 1:
The patent creates composite anions combining the metal-deposition-supporting alkoxide ligands with highly electronegative fluorinated groups. This composite structure allows the alkoxide portion to facilitate reversible Mg and Ca deposition while the fluorinated groups extend the anodic stability window through their electron-withdrawing effects and high oxidation resistance.
Solution Approach 2:
The patent merges the functional benefits of different ligand types (alkoxide for metal deposition, fluorinated groups for anodic stability) into a single integrated anion structure, achieving both reversible metal electrochemistry and extended voltage stability.
4Reliability
If monocarboranes are used, then electrochemical performance is exceptional, but synthesis is costly and involved
Solution Approach 1:
The patent replaces expensive, difficult-to-synthesize monocarborane anions with more accessible borate and aluminate analogs that can be prepared from commercially available starting materials through straightforward synthesis routes, achieving comparable electrochemical performance at lower cost and complexity.
Solution Approach 2:
The patent changes the core structure from monocarborane to borate/aluminate while maintaining the fluorinated alkoxide ligand framework, achieving similar electrochemical performance with significantly improved synthetic accessibility and reduced cost.
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 new silicate anions provide enhanced stability, solubility, and redox window, supporting reversible metal deposition and stripping, particularly for Mg and Ca, while also enabling diverse coordination chemistry applications.
Implementation Method 1
Weakly-coordinating anions (WCAs) facilitate diverse chemistry stemming from access to highly electrophilic centers... Weak cation-anion interaction
Implementation Method 2
Bulkier, less nucleophilic WCA-supported electrolytes impart higher ionic conductivity, stability, and reversibility
Data Source
AI summary
A new class of weakly coordinating anions (WCA) based on silicates is disclosed. Facile tuning of sterics and solubility of the disclosed WCA may be achieved via variation of R groups. The anions support a range of cations employed in chemical reactivity, including ether-free alkali cations, Ag+, Ph3C+, Fc+, [NiI(COD)2]+. In one aspect, [Pd(dppe)(NCMe)Me]+ may be generated by salt metathesis or protonation of a metal-alkyl bond, showcasing the ability of the anions to support applications in coordination chemistry and catalysis. Electrochemical studies on the [Bu4N]+ variant show an exceptionally wide stability window for the MeSiF24<sup2>−</sup2> anion of 7.5 V in MeCN. CV experiments demonstrate reversible Mg deposition and stripping.