Ether Electrolyte Additives for Stable Sodium Battery Cycling
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Solution Overview
Problem
Sodium-ion secondary batteries face challenges due to lower energy density, volume expansion, and sodium metal's reactivity with electrolytes, leading to reduced cyclic reversibility and safety issues.
Innovation Solution
An electrolyte system with ether organic solvent and additives like phosphite or borate additives forms a protective film on the positive electrode, stabilizing the electrolyte and reducing oxidative decomposition, while a conductive substrate facilitates sodium deposition, enhancing coulombic efficiency and cycling performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If sodium metal is used as negative electrode to increase energy density, then capacity is improved, but violent reactions with electrolyte occur reducing safety
Solution Approach 1:
A protective film is introduced as an intermediary layer between the sodium metal negative electrode and the ether-based electrolyte. This film acts as a mediator that prevents direct contact and violent reactions while still allowing ion transport, thus maintaining high energy density while improving safety
Solution Approach 2:
The protective film is formed preliminarily on the sodium metal surface before the battery operates. This pre-formed layer provides preliminary protection against the electrolyte, preventing the violent reactions that would otherwise occur when sodium metal contacts the ether-based electrolyte
2Productivity
If ether organic solvent is used in electrolyte to improve ion conductivity, then coulombic efficiency is improved, but oxidative decomposition on positive electrode increases
Solution Approach 1:
The oxidative decomposition of the ether organic solvent, which initially appears harmful, is converted into a beneficial process by controlling it to form a protective film on the positive electrode. This film, while resulting from oxidation, actually protects the electrode and stabilizes the electrolyte, transforming the harmful effect into a protective mechanism
Solution Approach 2:
The chemical composition and structure parameters of the electrolyte are modified by selecting specific ether organic solvents and adding additives. These parameter changes reduce the oxidation potential and improve electrochemical stability, allowing the system to maintain high coulombic efficiency while minimizing oxidative decomposition
3Quantity of substance
If sodium-ion battery system is adopted to address lithium resource scarcity, then material availability is improved, but volume expansion during intercalation reduces cyclic reversibility
Solution Approach 1:
Protective films are introduced as flexible, thin interfaces between the electrode materials and the electrolyte. These films accommodate the volume expansion and contraction of sodium-ion materials during charging and discharging cycles without breaking or delaminating, thus maintaining cyclic reversibility despite the larger ionic radius of sodium
Solution Approach 2:
The protective films serve as a cushioning layer that is formed beforehand on the electrode surfaces. This preliminary cushioning structure absorbs and distributes the mechanical stress from volume expansion during sodium insertion, preventing structural degradation and maintaining long-term cyclic stability
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 solution improves the coulombic efficiency and cycling performance of sodium-ion batteries by stabilizing the electrolyte and preventing oxidative decomposition, thus addressing the reactivity and volume expansion issues.
Implementation Method 1
the trivalent boron atom in the borate additive has an empty P-orbital, entirely exhibits Lewis acidity, can coordinate with anions to increase the transference number of lithium/sodium ions, and can also coordinate with oxygen atoms in the ether organic solvent molecules
Implementation Method 2
the first additive is relatively stable with respect to sodium metal and can preferentially undergo oxidative decomposition on a surface of an oxide positive electrode to form a CEI film containing a boron or phosphorus compound
Implementation Method 3
the first additive forms a film on a positive electrode surface, effectively reducing the oxidative decomposition of the ether solvent on the positive electrode surface, thereby reducing the shuttling of oxidative decomposition products between positive and negative electrodes
Data Source
AI summary
A secondary battery, an electrolyte, and an electric apparatus. The secondary battery includes a positive electrode plate, an electrolyte, a separator, and a negative electrode current collector, where the electrolyte includes a non-aqueous solvent, an electrolytic salt, and an additive; the non-aqueous solvent includes an ether organic solvent; the additive includes a first additive; and the first additive includes one or more of a phosphite additive or a borate additive.