Silicon-Based Lithium Battery Electrolyte for Stable High-Temperature SEI
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Solution Overview
Problem
Lithium secondary batteries with silicon-based active materials face challenges due to volume expansion, leading to SEI film deterioration, electrolyte consumption, and reduced lifespan and storage performance, especially at high temperatures.
Innovation Solution
A lithium secondary battery design incorporating a non-aqueous electrolyte with a first additive, such as a coumarin-based compound, and a second additive like lithium fluoromalonato(difluoro)borate, which forms a flexible and durable SEI film on the negative electrode, mitigating volume expansion issues and enhancing high-temperature cycle and storage performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If silicon-based active material is used in the negative electrode, then battery capacity is improved, but volume expansion occurs causing SEI film deterioration and electrolyte consumption
Solution Approach 1:
The patent introduces a dual-additive system comprising a cyclic carbonate additive (10-50 wt% of total additives) and a chain carbonate additive (50-90 wt% of total additives) with specific molecular weight ranges (100-500 g/mol for cyclic, 500-2000 g/mol for chain). This parameter optimization enables the formation of an SEI film with balanced mechanical properties that can accommodate silicon's volume expansion while maintaining protective function.
Solution Approach 2:
The patent creates a composite SEI film structure through the synergistic interaction of two different additive types. The cyclic carbonate forms a rigid protective framework while the chain carbonate provides flexible matrix that can deform with volume changes. This composite structure resolves the contradiction between maintaining SEI film integrity and accommodating silicon expansion.
2Quantity of substance
If silicon-based active material undergoes intercalation and deintercalation, then battery capacity is improved, but continuous electrolyte consumption occurs
Solution Approach 1:
The patent employs additives that react preferentially during initial cycles to form a stable SEI film before the electrolyte can undergo harmful side reactions. The cyclic carbonate additive (e.g., EC, PC) and chain carbonate additive (e.g., DMC, DEC) create a protective barrier in advance, preventing subsequent electrolyte decomposition during silicon's repeated volume changes.
Solution Approach 2:
The patent converts the harmful volume expansion of silicon into a beneficial effect by designing an SEI film that utilizes this expansion to maintain its protective properties. The chain carbonate additive's flexible structure allows the SEI film to expand and contract with the silicon, preventing film rupture and the associated electrolyte consumption that would occur with rigid films.
3Reliability
If SEI film thickness increases due to silicon volume expansion, then electrode protection is improved, but capacity and lifespan degrade
Solution Approach 1:
The patent creates an SEI film with spatially varying properties through the dual-additive system. The cyclic carbonate component concentrates in regions experiencing high stress to provide rigid protection, while the chain carbonate component distributes throughout the matrix to provide flexibility. This local quality differentiation allows the film to protect against degradation while maintaining thin overall thickness to prevent capacity loss.
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 significantly improves the battery's high-temperature cycle lifespan and storage performance by preventing SEI film breakage and electrolyte consumption, ensuring better durability and restorability of the film, thus extending the battery's lifespan and storage capacity.
Implementation Method 1
a film (SEI film) is formed on the positive electrode and/or the negative electrode in an initial activation process, and this may protect the positive electrode and the negative electrode over the running of batteries, and prevent electrolyte consumption caused by side reactions of the electrolyte
Implementation Method 2
the silicon-based active material brings about great changes in volume due to intercalation and deintercalation of lithium
Data Source
AI summary
A lithium secondary battery includes a negative electrode, a positive electrode positioned opposite to the negative electrode, a separator disposed between the negative electrode and the positive electrode, and a non-aqueous electrolyte, wherein the negative electrode includes a silicon-based active material, the silicon-based active material comprises a compound represented by SiOx, wherein 0≤x<2, the non-aqueous electrolyte includes a lithium salt, an organic solvent, and an additive, the additive includes a first additive and a second additive, the first additive includes a coumarin-based compound represented by Formula 1, and the second additive includes at least one of lithium fluoromalonato(difluoro)borate (LiFMDFB), lithium difluoro(oxalato)borate (LiDFOB), lithium difluorophosphate (LiDFP), or lithium difluorobis-(oxalate)phosphate (LiDFOP):wherein R and n are described herein.