Silicon-Graphite Composite Electrode with Oxolane Electrolyte
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Solution Overview
Problem
Lithium-ion batteries face challenges with graphite electrodes due to high irreversibility and capacity loss in cycling, which silicon electrodes mitigate but are prone to mechanical damage from volume expansion, necessitating a compatible electrolyte for silicon-graphite composite electrodes to achieve high capacity retention and coulombic efficiency.
Innovation Solution
A lithium-ion battery cell with a silicon-graphite composite negative electrode and a non-aqueous electrolyte comprising a lithium salt and oxolane or oxane compounds, such as LiTFSI, which provides a compatible environment for stable cycling and high coulombic efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If graphite is used as the negative electrode material, then the electrode structure is stable, but the specific capacity is limited to 320 mAh/g and there is strong irreversibility on first charge
Solution Approach 1:
The patent employs a composite negative electrode consisting of silicon particles (5-50 wt%), graphite particles (40-90 wt%), and conductive carbon (1-10 wt%). This composite structure combines the high capacity advantage of silicon with the structural stability and conductivity of graphite, achieving both high specific capacity and good cycling stability.
2Quantity of substance
If silicon is used as the negative electrode material, then the specific capacity increases to 3580 mAh/g, but the volume expansion reaches 280% causing mechanical damage and loss of contact with current collector
Solution Approach 1:
The patent uses a composite structure where silicon particles (5-50 wt%) are embedded in a graphite matrix (40-90 wt%). The graphite component acts as a buffer that accommodates the 280% volume expansion of silicon during lithiation, preventing mechanical damage and maintaining electrode integrity while still enabling high capacity.
Solution Approach 2:
The graphite matrix surrounding silicon particles functions as a flexible buffer layer that can deform to accommodate silicon's volume expansion during cycling, preventing crack formation and maintaining electrical contact with the current collector.
3Reliability
If a conventional electrolyte is used with silicon-graphite composite electrode, then the electrode compatibility is poor, but using a specific electrolyte composition improves capacity retention and coulombic efficiency
Solution Approach 1:
The patent optimizes the electrolyte composition by specifying precise proportions: cyclic carbonate (10-30 vol%), chain carbonate (70-90 vol%), and lithium salt (0.5-2.0 M concentration). These parameter optimizations enhance the electrolyte's compatibility with silicon-graphite composite electrodes, improving capacity retention and coulombic efficiency.
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 electrolyte combination with a silicon-graphite composite material enhances electrochemical performance, maintaining high capacity retention and coulombic efficiency throughout cycles, mitigating the mechanical issues associated with silicon expansion.
Implementation Method 1
an electrolyte comprising a lithium salt and at least one compound chosen from oxolane compounds, oxane compounds and mixtures thereof
Implementation Method 2
Batteries of the lithium-ion type operate on the principle of insertion-de-insertion (or lithiation-delithiation) of lithium
Data Source
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AI summary
The invention relates to an electrochemical cell for a lithium battery comprising two electrodes of opposite polarity, one of the electrodes having, as active material, a graphite-silicon composite material and comprising an electrolyte comprising a lithium salt and at least one compound selected from oxolane compounds, oxane compounds and mixtures thereof.