Silicon Negative Electrode Separator Modulus Optimization
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Solution Overview
Problem
Lithium-ion secondary batteries using silicon or silicon oxide as negative electrode materials face significant volume expansion issues, leading to decreased charging/discharging cycle characteristics due to friction at the separator interface and peeling of active materials, which limits their capacity and durability.
Innovation Solution
A lithium-ion secondary battery design where the average 3% modulus strength of the separator is optimized to be 0.079 or less compared to the negative electrode, using a negative electrode active material layer with silicon and silicon oxide as the main component, and maintaining an arithmetic average surface roughness of 1 to 4 μm to prevent peeling and enhance mechanical conformity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If silicon or silicon oxide is used as negative electrode active material to achieve high capacity, then the theoretical capacity increases significantly, but volume expansion occurs during lithium intercalation causing active material detachment and decreased cycle characteristic
Solution Approach 1:
The invention changes the mechanical parameter (modulus strength) of the separator to match the expansion characteristics of the silicon-based negative electrode. By setting the separator's modulus strength to 0.039 N/50mm or less, the separator can elastically expand and contract with the negative electrode during charging/discharging cycles, preventing detachment and maintaining cycle stability while preserving high capacity.
2Quantity of substance
If silicon or silicon oxide is used as negative electrode active material, then high capacity is achieved, but friction occurs at separator interface causing peeling and reduced cycle characteristic
Solution Approach 1:
The invention modifies the mechanical parameter of the separator by controlling its modulus strength to be 0.039 N/50mm or less. This parameter change allows the separator to flexibly accommodate the volume changes of the silicon-based active material during lithium insertion/extraction, thereby reducing friction at the separator interface and preventing peeling of active material or conductive auxiliary agents.
3Strength
If the separator modulus strength is increased to maintain structural stability, then mechanical strength is improved, but friction increases causing active material peeling and decreased cycle characteristic
Solution Approach 1:
The invention optimizes the separator's modulus strength parameter to a specific range (0.039 N/50mm or less) that balances mechanical stability with flexibility. This optimized parameter allows the separator to maintain sufficient structural integrity while simultaneously accommodating the expansion and contraction of the silicon-based negative electrode, thereby preventing active material peeling and improving cycle characteristic.
4Quantity of substance
If the negative electrode expands during charging, then high capacity is achieved, but the separator cannot conform to the expansion causing friction and peeling
Solution Approach 1:
The invention changes the mechanical parameter of the separator (modulus strength ≤ 0.039 N/50mm) to enable it to conform to the expansion of the negative electrode during charging. The low modulus strength allows the separator to elastically deform and follow the volume changes of the silicon-based active material, maintaining intimate contact and preventing friction-induced peeling while preserving high capacity.
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
This design improves the charging/discharging cycle characteristics by suppressing friction and peeling, allowing for higher capacity retention and reduced resistance, thereby enhancing the battery's overall performance and longevity.
Implementation Method 1
When the value (M3s/M3a) obtained by dividing M3s by M3a is 0.079 or less, since the separator conforms to the expansion of the negative electrode accompanying the charging/discharging, friction at an interface between the negative electrode and the separator is suppressed
Implementation Method 2
Silicon is electrochemically intercalating and deintercalating lithium-ions, and is capable of realizing charging/discharging of a very large capacity compared to graphite
Implementation Method 3
since these alloy-based material forms a lithium-silicon alloy during intercalation of lithium, and is changed from an original crystal structure, very large volume expansion is accompanied
Data Source
AI summary
In the invention, a lithium-ion secondary battery, in which a value obtained by dividing average 3% modulus strength of a separator by average 3% modulus strength of a negative electrode including a negative electrode active material layer containing silicon and silicon oxide as a main component is 0.079 or less, is used.