Sodium-Ion Battery Electrolyte for Wettability and Pressure Stability
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Solution Overview
Problem
Sodium-ion batteries face performance issues such as poor cycling and self-discharge at elevated temperatures, high viscosity leading to poor wettability with commercial separators, and increased cell pressure causing circuit failure, due to the differences in solubility of Na-based products compared to Li-based counterparts.
Innovation Solution
A non-aqueous electrolyte composition comprising a mixture of ethylene carbonate, dimethyl carbonate, and additives like tris(trimethylsilyl)phosphite (TMSPi), succinonitrile, and difluoro(oxalato)borate (NaODFB) is developed, which improves the stability of the solid electrolyte interphase and cathode electrolyte interphase, reducing oxidation of the electrolyte solvent and gaseous by-product formation, while maintaining good wettability and power performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a specific electrolyte based on EC-PC and NaPF6 with additives (NaODFB, SN, PS, VC) is implemented, then the power rate and cycle life are improved, but the wettability with commercial polyolefin separators deteriorates and viscosity increases
Solution Approach 1:
The patent changes the chemical composition parameters of the electrolyte by replacing VC with TMSPi and adjusting additive concentrations. This parameter modification maintains the protective film-forming capability while improving wettability and reducing viscosity, allowing the electrolyte to effectively wet commercial polyolefin separators without sacrificing cycle life performance
Solution Approach 2:
The patent copies the successful film-forming mechanism from VC (vinylene carbonate) but uses TMSPi (tris(trimethylsilyl)phosphite) as an alternative additive that provides similar protective interphase formation while having superior wettability properties. This substitution preserves the beneficial effects of film-forming additives while eliminating their negative impact on separator wetting
2Ease of operation
If another specific electrolyte based on EC and DMC with NaPF6 and additives (NaODFB, VC, TMSPi) is implemented, then the wettability with commercial separators is improved, but cell pressure continuously increases leading to CID break and cell failure
Solution Approach 1:
The patent introduces SN (succinonitrile) as an intermediary substance that mediates between the electrolyte components and electrode surfaces. SN forms a stable protective layer that prevents excessive gas generation and pressure buildup during cycling, while also maintaining good wettability properties. This intermediary additive acts as a pressure-regulating agent that eliminates the harmful pressure effects
3Reliability
If classical mixtures of EC, PC and DMC with 1 mol/L NaPF6 are used, then the performance at room temperature is excellent, but the cycling and self-discharge performance at 55°C deteriorates
Solution Approach 1:
The patent creates a composite electrolyte system combining multiple components (EC, PC, DMC, NaPF6, NaODFB, SN, TMSPi) that work synergistically. The composite formulation provides thermal stability at elevated temperatures while maintaining room temperature performance, as each component contributes specific properties that compensate for temperature-related degradation
Solution Approach 2:
The patent modifies the electrolyte composition parameters by adding specific additives (NaODFB, SN, TMSPi) in optimized concentrations. These parameter changes enhance the thermal stability of the electrolyte system, preventing the deterioration of cycling and self-discharge performance at 55°C while preserving excellent room temperature operation
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 electrolyte composition enhances the power rate, cycle life, and specific energy of sodium-ion batteries while preventing pressure increases and maintaining effective wettability with commercial separators, leading to stable operation across varying temperatures.
Implementation Method 1
succinonitrile helps in protecting the positive electrode by forming stable CEI and reduce the oxidation of electrolyte solvent
Implementation Method 2
reduce the oxidation of electrolyte solvent
Implementation Method 3
the combination of additives comprises at least tris(trimethylsilyl)phosphite (TMSPi) and succinonitrile (SN)
Implementation Method 4
an electrolyte composition comprising at least one sodium salt dissolved in a solvent
Implementation Method 5
at least one sodium salt dissolved in a solvent
Data Source
AI summary
An electrolyte composition including at least one sodium salt dissolved in a solvent and a combination of additives, wherein: the solvent includes at least one compound selected from the group consisting of ethylene carbonate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, propylene carbonate, a carboxylate ester such as methyl acetate, ethyl acetate, ethyl propionate and methyl propionate, 4-fluorotoluene, 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether, di-fluoro ethylene carbonate, ethyl difluoroacetate and diglyme, and the combination of additives comprises at least tris(trimethylsilyl)phosphite (TMSPi) and succinonitrile (SN).