Silicon Composite Anode Powder for Lithium-Ion Batteries
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Solution Overview
Problem
Lithium-ion batteries face performance limitations due to the large volume expansion of silicon-based anode materials during charging and discharging, leading to mechanical degradation and excessive Solid-Electrolyte Interface (SEI) formation, which reduces cycle performance and energy density.
Innovation Solution
A composite powder with silicon-based domains dispersed in a matrix material, where at least 98% of the silicon-based domains are present as agglomerates with a maximum size of 3µm or less, or are not agglomerated at all, to improve dispersion and reduce SEI formation, enhancing electrochemical performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If silicon-based materials are used as anode active material to improve energy density, then theoretical capacity increases to 4200mAh/g, but large volume expansion of 300% during charging occurs leading to mechanical degradation
Solution Approach 1:
The silicon-based material is divided into small domains with average size smaller than 500nm and preferably smaller than 150nm. This segmentation reduces the overall volume expansion stress and prevents catastrophic mechanical failure while maintaining high theoretical capacity.
Solution Approach 2:
The invention uses composite particles where silicon domains are mixed with a matrix material, usually a carbon-based material. This composite structure provides mechanical support to the silicon domains, accommodating the 300% volume expansion during lithiation without causing mechanical degradation.
2Reliability
If silicon domains are reduced to submicron or nanosized to alleviate volume change effects, then mechanical degradation is reduced, but particle aggregation and dispersion issues arise
Solution Approach 1:
The submicron or nanosized silicon domains are combined with a matrix material to form composite particles. This composite approach prevents aggregation of the fine silicon domains while maintaining their small size benefits, solving the dispersion control issue.
3Use of energy by moving object
If thick SEI forms on the anode during lithiation, then initial capacity is achieved, but lithium availability is reduced leading to poor cycle performance
Solution Approach 1:
The SEI layer that forms on the silicon surface acts as a passivation layer. While it initially consumes lithium, it subsequently protects the silicon domains from further unwanted reactions. The small domain size ensures that this initial SEI formation does not completely deplete available lithium.
Solution Approach 2:
The harmful SEI formation process is converted into a beneficial protective mechanism. The SEI layer, while initially consuming lithium, subsequently protects the silicon domains from further degradation and unwanted reactions, improving long-term cycle performance.
4Reliability
If thick SEI forms on silicon surface, then passivation is achieved, but electrical resistance increases limiting charging and discharging rates
Solution Approach 1:
Dividing silicon into small domains reduces the total surface area requiring SEI formation, thereby reducing the overall electrical resistance impact while maintaining adequate passivation protection.
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 results in improved cycle performance and reduced SEI formation, leading to increased electrochemical performance and energy storage capacity of lithium-ion batteries.
Implementation Method 1
one drawback of using a silicon based electrochemically active material in an anode is its large volume expansion during charging, which is as high as 300% when the lithium ions are fully incorporated, e.g. by alloying or insertion, in the anode's active material - a process often called lithiation
Implementation Method 2
a thick SEI, a Solid-Electrolyte Interface, may be formed on the anode. An SEI is a complex reaction product of the electrolyte and lithium
Data Source
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AI summary
Powder comprising particles comprising a matrix material and silicon-based domains dispersed in this matrix material, whereby either part of the silicon-based domains are present in the form of agglomerates of silicon-based domains whereby at least 98% of these agglomerates have a maximum size of 3μm or less, or the silicon-based domains are not at all agglomerated into agglomerates.