Silicon Anode Electrolyte Additives for Stable SEI Formation
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Solution Overview
Problem
Lithium-silicon alloys in silicon-based negative electrode materials for electrochemical apparatuses are highly reactive, leading to rapid electrolyte consumption and poor cycling stability due to the formation of lithium-silicon alloys that attack solvent molecules, causing cracking and poor performance.
Innovation Solution
Incorporating a compound of formula I, such as NO2-R1-R2, with fluoroethylene carbonate (FEC) in the electrolyte to form an interfacial film rich in inorganic substances like Li3N and Li2O, which mitigates electrolyte decomposition and enhances the stability of the solid electrolyte interface (SEI) film, along with dinitrile and sulfur-oxygen double bond-containing cyclic compounds to improve film integrity and ion transport.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If silicon-based materials are used as negative electrode material to increase specific capacity, then energy density is improved, but cycling stability deteriorates due to rapid electrolyte consumption and SEI film instability
Solution Approach 1:
The patent introduces a mediator substance (cyclic carboxylate compound) that acts as an intermediary between the silicon-based negative electrode material and the electrolyte. This compound preferentially reacts with lithium ions to form a stable interfacial film that prevents direct contact between the reactive lithium-silicon alloys and the electrolyte solvent molecules, thereby reducing electrolyte consumption and improving cycling stability while maintaining high energy density
Solution Approach 2:
The patent changes the chemical composition parameters of the electrolyte interface by introducing cyclic carboxylate compounds (such as γ-butyrolactone, γ-valerolactone, or δ-valerolactone) at specific concentrations (0.1-5 wt%). This parameter change modifies the interfacial chemistry to form a more stable SEI film that can accommodate the expansion and contraction of silicon particles during cycling, resolving the contradiction between high capacity and cycling stability
2Use of energy by moving object
If silicon-based materials are used to achieve ultra-high specific capacity, then energy density is improved, but electrolyte consumption increases due to high reactivity of lithium-silicon alloys
Solution Approach 1:
The cyclic carboxylate compound serves as a protective intermediary that forms a stable interfacial layer between the highly reactive lithium-silicon alloys and the electrolyte. This intermediary film prevents the direct attack of solvent molecules on the alloy surface, significantly reducing electrolyte decomposition and consumption while allowing the high-capacity silicon material to function effectively
Solution Approach 2:
The patent applies preliminary action by having the cyclic carboxylate compound react first with lithium ions during the initial charging cycles to form a pre-stabilized interfacial film. This preliminary film formation occurs before the electrolyte can be attacked by the reactive lithium-silicon alloys, preventing subsequent electrolyte consumption and establishing a protective barrier that persists throughout cycling
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 cycling stability and energy density of electrochemical apparatuses by reducing electrolyte consumption and maintaining ion transport, thereby enhancing the performance and longevity of the apparatus.
Implementation Method 1
Incorporating a compound of formula I, such as NO2-R1-R2, with fluoroethylene carbonate (FEC) in the electrolyte to form an interfacial film rich in inorganic substances like Li3N and Li2O
Implementation Method 2
which mitigates electrolyte decomposition and enhances the stability of the solid electrolyte interface (SEI) film
Implementation Method 3
lithium-silicon alloys are highly reactive, readily attacking solvent molecules in the electrolyte. This leads to rapid electrolyte consumption... the compound of formula I lowers the consumption rate of fluoroethylene carbonate
Implementation Method 4
Controlling the mass percentage of the silicon element within the foregoing range can enable the electrochemical apparatus to provide the space required for the expansion of silicon particles in the process of charging and discharging. This effectively mitigates issues such as cracking of the negative electrode active material
Data Source
AI summary
An electrochemical apparatus includes a negative electrode plate and an electrolyte. The negative electrode plate includes a negative electrode material layer. The negative electrode material layer includes a silicon-based material. The silicon-based material includes silicon element, and based on a total mass of the negative electrode material layer, a mass percentage of the silicon element is 30% to 60%. The electrolyte includes fluoroethylene carbonate and a compound of formula I. R1 and R2 are each independently selected from hydrogen atom, fluorine atom, substituted or unsubstituted C1-C5 alkyl group, substituted or unsubstituted C6-C10 aryl group, and substituted or unsubstituted C2-C6 carboxylate group, and when substituted, the substituents on the carboxylate group, the alkyl group, and the aryl group are fluorine atoms.