Silicon-Anode Lithium-Ion Electrolyte for Stable SEI Formation
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Solution Overview
Problem
The expansion and contraction of silicon-based negative electrode active materials in lithium-ion secondary batteries cause the solid-electrolyte interface (SEI) to crack, leading to continuous decomposition of the electrolyte and growth of the SEI, which reduces coulombic efficiency.
Innovation Solution
A lithium-ion secondary battery design that includes a silicon-based negative electrode active material layer, a separator layer, and a positive electrode active material layer impregnated with an electrolyte solution containing an ionic liquid and lithium ions, where the ionic liquid comprises phosphonium ions and bis(fluorosulfonyl)imide ions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If silicon-based negative electrode active material is used to increase capacity, then energy density is improved, but SEI cracks and continuous decomposition occur reducing coulombic efficiency
Solution Approach 1:
The patent applies preliminary action by pre-forming a stable SEI layer using an ionic liquid electrolyte containing phosphonium ions and bis(fluorosulfonyl)imide ions before normal battery operation. This pre-formed SEI layer is designed to accommodate silicon expansion and contraction without cracking, preventing continuous electrolyte decomposition during subsequent charge-discharge cycles.
Solution Approach 2:
The patent changes the chemical composition parameters of the electrolyte by introducing specific ionic liquids with phosphonium ions and bis(fluorosulfonyl)imide ions. This parameter change modifies the SEI formation characteristics, creating a more stable and flexible protective layer that can handle silicon's volume changes while maintaining low electrolyte decomposition.
2Reliability
If SEI layer grows to protect electrode material, then protection is improved, but electrolyte continues to decompose reducing coulombic efficiency
Solution Approach 1:
The patent modifies the electrolyte composition parameters by incorporating ionic liquids with specific phosphonium ions and bis(fluorosulfonyl)imide ions. This changes the SEI formation mechanism to produce a stable protective layer that prevents further electrolyte decomposition, simultaneously achieving good protection and high coulombic efficiency.
Solution Approach 2:
The patent creates a composite SEI layer through the interaction of multiple ionic liquid components (phosphonium ions and bis(fluorosulfonyl)imide ions) with the silicon-based electrode material. This composite structure provides enhanced protective properties while maintaining stability and minimizing continuous electrolyte consumption.
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 inclusion of phosphonium ions in the electrolyte solution forms a stable SEI that effectively manages the expansion and contraction of the silicon-based negative electrode active material, thereby improving coulombic efficiency and reducing SEI overformation.
Implementation Method 1
it is known that a solid-electrolyte interface (SEI) is formed at an interface between an electrode-active material and an electrolyte solution
Implementation Method 2
SEI functions as a protective layer that protects the electrode active material and the electrolyte solution from corroding and other undesirable side reactions
Implementation Method 3
an electrolyte solution, wherein the electrolyte solution comprises an ionic liquid and a lithium ion
Data Source
AI summary
A lithium-ion secondary battery having improved coulombic efficiency. A lithium ion secondary battery comprises, a negative electrode active material layer, a separator layer, and a positive electrode active material layer in the order mentioned, wherein the negative electrode active material layer comprises a silicon-based negative electrode active material, and wherein the negative electrode active material layer, the separator layer, and the positive electrode active material layer are impregnated with an electrolyte solution, wherein the electrolyte solution comprises an ionic liquid and a lithium ion, wherein the ionic liquid comprises a phosphonium ion and a bis(fluorosulfonyl)imide ion.