Silicon Oxide-Graphite Anodes for Stable High-Energy Li-Ion Cells
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Lithium ion batteries face challenges with high irreversible capacity loss and poor cycling stability due to structural changes and large volume expansions in silicon-based negative electrodes, which affect the cycling efficiency and energy density.
Innovation Solution
The development of a lithium ion cell design incorporating a negative electrode with a blend of silicon oxide and graphite, combined with nanoscale conductive carbon and a polymer binder, specifically using a high tensile strength polyimide binder with a more elastic component, to stabilize the cycling performance and maintain energy density.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If silicon-based negative electrode materials are used to increase energy density, then capacity is improved, but cycling stability deteriorates due to large volume expansions and structural changes
Solution Approach 1:
The silicon-based electrode is segmented into nanoscale particles (1-100 nm diameter) to reduce the overall volume expansion impact on the electrode structure during lithiation/delithiation cycles
Solution Approach 2:
A composite material system is used comprising silicon oxide (SiOx) nanoparticles dispersed in a conductive carbon matrix, where the carbon provides structural stability while silicon oxide provides high capacity, resolving the contradiction between capacity and cycling stability
2Quantity of substance
If high capacity silicon materials are used, then energy density is improved, but irreversible capacity loss increases
Solution Approach 1:
Conductive carbon acts as an intermediary between silicon oxide particles and the electrolyte, facilitating stable lithium ion transport while preventing direct contact that would cause excessive SEI formation and irreversible capacity loss
Solution Approach 2:
The oxidation state of silicon is changed from Si(0) to SiOx where 0 < x ≤ 2, which reduces the volume expansion during lithiation from ~300% for pure silicon to ~150% for SiOx, thereby reducing irreversible capacity loss while maintaining high capacity
3Quantity of substance
If silicon oxide-based materials are used to achieve high capacity, then discharge capacity is improved, but structural integrity deteriorates due to volume changes during cycling
Solution Approach 1:
A flexible conductive carbon matrix envelops the rigid silicon oxide particles, providing a compliant structure that accommodates volume changes during cycling while maintaining electrical conductivity and structural integrity
Solution Approach 2:
Silicon oxide nanoparticles are nested within the conductive carbon matrix structure, allowing the carbon to provide structural support and accommodate the volume changes of silicon oxide during lithiation and delithiation cycles
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 achieves long-term cycling stability with over 600 charge/discharge cycles while maintaining at least 80% of the initial discharge specific capacity, and achieves a high energy density of at least 235 Wh/kg, suitable for automotive and consumer electronics applications.
Implementation Method 1
lithium intercalation/alloying
Implementation Method 2
lithium intercalation/alloying
Implementation Method 3
polymer binder with an elastic modulus of no more than about 2.4 GPa and an elongation of at least about 35%
Implementation Method 4
nanoscale conductive carbon
Data Source
AI summary
Improved negative electrodes can comprise a silicon based active material blended with graphite to provide more stable cycling at high energy densities. In some embodiments, the negative electrodes comprise a blend of polyimide binder mixed with a more elastic polymer binder with a nanoscale carbon conductive additive. The silicon-based blended graphite negative electrodes can be matched with positive electrodes comprising nickel rich lithium nickel manganese cobalt oxides to form high energy density cells with good cycling properties.