Aromatic Phosphite Stabilizer for Lithium Battery Electrolytes
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Solution Overview
Problem
Nonaqueous electrolytes in lithium and lithium ion batteries face thermal instability due to the decomposition of lithium hexafluorophosphate (LiPF6) caused by phosphorus pentafluoride (PF5), which leads to hydrolysis and corrosion, reducing battery performance.
Innovation Solution
Incorporating an aromatic phosphite compound as a stabilizer in the electrolytic solution, which forms complexes with PF5, thereby reducing decomposition and hydrolysis of halogenated lithium salts, enhancing thermal stability and shelf life at high temperatures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If LiPF6 is used as the electrolyte salt, then electrochemical stability and conductivity are improved, but thermal stability deteriorates due to decomposition at elevated temperatures
Solution Approach 1:
A Lewis base additive is introduced as an intermediary substance that selectively reacts with PF5 to form stable complexes. This mediator prevents PF5 from catalyzing the decomposition of LiPF6 and reacting with solvents, thereby protecting the electrolyte system from thermal degradation while maintaining the electrochemical benefits of LiPF6
Solution Approach 2:
The harmful PF5 decomposition product is converted into a beneficial complex through reaction with the Lewis base. Instead of allowing PF5 to cause decomposition and polymerization, it is transformed into a stable complex that prevents further harmful reactions, turning the source of thermal instability into a protective mechanism
2Reliability
If LiPF6 is used as the electrolyte salt, then conductivity is improved, but hydrolysis resistance deteriorates due to reaction with moisture and protic impurities
Solution Approach 1:
The Lewis base acts as a protective intermediary that preferentially reacts with PF5 to form stable complexes, preventing PF5 from reacting with moisture and protic impurities. This shielding effect protects LiPF6 from hydrolysis while maintaining the desired conductivity properties
3Temperature
If PF5 is removed or deactivated to prevent decomposition, then thermal stability is improved, but the ability to maintain conductivity may deteriorate
Solution Approach 1:
The Lewis base selectively complexes with PF5, removing its harmful catalytic activity while the complex itself remains electrochemically stable and conductive. This approach maintains ionic conductivity through the complexed species while eliminating the decomposition pathways associated with free PF5
Solution Approach 2:
The chemical state of PF5 is changed from a free, highly reactive species to a complexed, stable species. This parameter change (from free PF5 to Lewis base-PF5 complex) fundamentally alters the thermal stability and reactivity profile while maintaining electrochemical 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 aromatic phosphite stabilizes electrolytic solutions containing halogenated lithium salts, increasing their stability and reducing decomposition, resulting in improved thermal stability and long-term performance of lithium and lithium ion batteries.
Implementation Method 1
Zhang et al. found that tris(2,2,2-trifluoroethyl)phosphite, which has a Lewis basic P(III) center, can stabilize an electrolyte of 1.2M LiPF6 in EC/PC/EMC (3:3:4) for two weeks at 60° C.
Implementation Method 2
This deactivation or removal of PF5 can be achieved by complexing PF5 with a Lewis base.
Implementation Method 3
LiPF6+H2O→2HF+LiF+POF3 (2) Hydrolysis of LiPF6 (Reaction 2) generally occurs due to the presence of protic impurities such as moisture, alcohols and acidic impurities in the electrolytic solution.
Implementation Method 4
The charge flow between electrodes is maintained by an ionically conducting solute, i.e., a salt.
Data Source
AI summary
The invention relates to the use of aromatic phosphite compounds as stabilizers for nonaqueous electrolytic solutions containing halogenated salts such as LiPF6 and LiBF4. The electrolyte containing such a phosphite exhibits excellent shelf life storage at ambient and high temperatures. The electrolytic solution is suitable for use in electrochemical cells such as lithium (ion) rechargeable batteries and supercapacitors.