Pyrocarbonate Electrolytes for Silicon Anode SEI Stability
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Solution Overview
Problem
High capacity active materials in lithium ion batteries, such as silicon, exhibit poor cycle life due to mechanical instability and unstable solid electrolyte interphase (SEI) layers, leading to rapid capacity fading and reduced performance.
Innovation Solution
The use of novel electrolytes containing pyrocarbonates, such as dimethyl pyrocarbonate, and fluorinated carbonates, which improve the stability of the SEI layer and reduce capacity fading, with specific formulations like dimethyl pyrocarbonate and mono-fluoroethylene carbonate enhancing the cycle life of lithium ion batteries.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If high capacity active materials like silicon are used in lithium ion batteries, then energy density is improved, but cycle life deteriorates due to mechanical instability and unstable SEI layers
Solution Approach 1:
The patent changes the chemical composition parameters of the electrolyte by introducing pyrocarbonates (specifically dimethyl pyrocarbonate or DMPC) and fluorinated carbonates (specifically mono-fluoroethylene carbonate or FEC) into the electrolyte formulation. These chemical parameter changes modify the SEI layer formation and stability characteristics, enabling high capacity silicon-based electrodes to maintain stable cycle life while achieving high energy density.
2Quantity of substance
If conventional electrolytes are used with high capacity active materials, then initial capacity is achieved, but capacity fading increases rapidly over cycles
Solution Approach 1:
The patent introduces pyrocarbonates and fluorinated carbonates as intermediary substances in the electrolyte that mediate between the high capacity active materials and the conventional electrolyte components. These intermediaries facilitate the formation of stable SEI layers that prevent rapid capacity fading while maintaining high initial capacity, effectively acting as a bridge that reconciles the incompatibility between high capacity materials and conventional electrolytes.
3Quantity of substance
If high capacity active materials are used, then battery capacity is improved, but mechanical stress on SEI layer increases leading to instability
Solution Approach 1:
The patent creates a composite electrolyte system by combining pyrocarbonates (DMPC), fluorinated carbonates (FEC), and conventional carbonate solvents (EC, DMC, DEC, EMC). This composite electrolyte formulation produces a composite SEI layer with enhanced mechanical strength and stability that can withstand the mechanical stress generated by high capacity active materials, thereby maintaining both high battery capacity and SEI layer 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
These electrolyte formulations significantly improve the cycle life of lithium ion batteries with high capacity active materials, maintaining Coulombic efficiency above 99.8% after 100 cycles and reducing mechanical stress on the SEI layer, thereby extending the battery's operational life.
Implementation Method 1
The selection of electrolytes may impact formation of solid electrolyte interphase (SEI) layers, ionic mobility, and various other factors that collectively impact the cycle life of a cell.
Data Source
AI summary
Provided are novel electrolytes for use in rechargeable lithium ion cells containing high capacity active materials, such as silicon, germanium, tin, and/or aluminum. These novel electrolytes include one or more pyrocarbonates and, in certain embodiments, one or more fluorinated carbonates. For example, dimethyl pyrocarbonate (DMPC) may be combine with mono-fluoroethylene carbonate (FEC). Alternatively, DMPC or other pyrocarbonates may be used without any fluorinated carbonates. A weight ratio of pyrocarbonates may be between about 0% and 50%, for example, about 10%. Pyrocarbonates may be combined with other solvents, such as ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), diethyl carbonate (DEC), and/or ethyl-methyl carbonate (EMC). Alternatively, pyrocarbonates may be used without such solvents. Experimental results conducted using electrochemical cells with silicon based electrodes demonstrated substantial improvements in cycle life when pyrocarbonate containing electrolytes were used in comparison with pyrocarbonate free electrolytes.