Isocyanate Electrolytes for Ni-Rich Silicon Li-Ion Cell Stability
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Solution Overview
Problem
Lithium-ion batteries with silicon-based negative electrodes face challenges due to volume expansion during lithiation and delithiation, leading to particle pulverization, loss of electrical contact, and unstable solid-electrolyte interface formation, resulting in capacity fading.
Innovation Solution
Incorporating a nickel-rich positive electroactive material with a silicon-based negative electroactive material and an electrolyte containing isocyanate functional groups, such as cyclopentyl isocyanate, to enhance the stability of the electrolyte interface and reduce side reactions, thereby improving cycling stability and discharge rate performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If silicon-based negative electroactive material is used to achieve high specific capacity, then capacity capability is improved, but volume expansion during lithiation and delithiation causes particle pulverization and unstable solid-electrolyte interface formation
Solution Approach 1:
An electrolyte additive containing isocyanate functional groups is introduced as an intermediary substance between the silicon-based negative electrode and the electrolyte. This additive forms a stable solid-electrolyte interface layer that mediates the interaction, preventing direct contact between the electrolyte and silicon surface, thereby reducing side reactions and stabilizing the interface during volume expansion and contraction cycles.
Solution Approach 2:
The chemical composition and properties of the solid-electrolyte interface are changed by introducing isocyanate-containing additives. These additives modify the interface parameters (chemical stability, mechanical properties) to accommodate the volume expansion of silicon during lithiation, transforming the unstable interface into a stable one that can withstand mechanical stress.
2Quantity of substance
If nickel-rich positive electroactive material is used to improve capacity capability, then energy density is improved, but transition metal migration occurs leading to performance degradation
Solution Approach 1:
The isocyanate-containing electrolyte additive acts as an intermediary that forms protective interface layers on both electrodes. At the nickel-rich positive electrode, this intermediary layer prevents transition metal ions from migrating into the electrolyte and depositing on the negative electrode, thereby maintaining electrochemical performance while preserving the high capacity benefits of nickel-rich materials.
3Device complexity
If conventional electrolyte composition is used to maintain simplicity, then device complexity is reduced, but side reactions at the electrode interface increase causing capacity fading
Solution Approach 1:
The electrolyte composition is modified by incorporating a small concentration (1-10 wt.%) of isocyanate-containing additive. This parameter change in composition fundamentally alters the interface chemistry, reducing side reactions and capacity fading without significantly increasing device complexity, as the additive integrates into the existing electrolyte system.
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 proposed electrolyte system improves the cycling stability and discharge rate performance of lithium-ion batteries by reducing surface activity and mitigating transition metal migration, resulting in higher capacity retention and improved electrochemical performance.
Implementation Method 1
an unstable solid-electrolyte interface (SEI) formation
Implementation Method 2
The electrolyte may include one or more isocyanate functional groups... to enhance the stability of the electrolyte interface
Implementation Method 3
The electrolyte is suitable for conducting lithium ions between the electrodes
Implementation Method 4
nickel-rich electroactive materials... capable of providing improved capacity capability... while allowing for additional lithium extraction
Data Source
AI summary
An electrochemical cell that cycles lithium ions includes a first electrolyte, a second electrode, a separating layer disposed between the first layer and the second layer. The first electrolyte includes a nickel-rich positive electroactive material that includes greater than or equal to about 80 mass % of nickel (Ni). The second electrode includes a silicon-based negative electroactive material. The electrochemical cell also includes an electrolyte in contact with at least one of the nickel-rich positive electroactive material in the first electrode and the silicon-based negative electroactive material in the second electrode. The electrolyte includes greater than or equal to about 1.5 wt. % to less than or equal to about 5 wt. % of an electrolyte additive. The electrolyte includes one or more isocyanate functional groups.