Silicon Oxide Negative Electrode with Heat Expandable Microcapsules
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Solution Overview
Problem
Silicon oxide-based negative electrodes in non-aqueous electrolyte secondary batteries are prone to internal short circuits, leading to heat generation and thermal runaway due to the high expansion and contraction coefficients, causing the electrolyte solution to react with the active material and result in further temperature rise.
Innovation Solution
Incorporating heat expandable microcapsules with a thermoplastic resin shell and thermal expansion agents into the negative electrode composite material layer, ensuring a ratio of silicon oxide to total active material of 30% or less and heat expandable microcapsules of 0.5% or more, with 70% or more in contact with silicon oxide, to prevent electrolyte solution reaction and suppress temperature rise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If silicon oxide is used as negative electrode active material to increase capacity, then battery capacity is improved, but thermal runaway risk increases due to high expansion/contraction coefficients causing void formation and electrolyte infiltration
Solution Approach 1:
Heat expandable microcapsules are incorporated into the negative electrode composite material layer before battery assembly. These microcapsules remain dormant during normal operation but automatically expand when exposed to heat from internal short circuits, filling voids formed by silicon oxide contraction and preventing electrolyte infiltration, thereby suppressing thermal runaway before it can develop
Solution Approach 2:
Heat expandable microcapsules act as an intermediary substance between the silicon oxide active material and the electrolyte solution. When activated by heat, they physically block the interface between these two components, preventing direct contact and the exothermic reactions that would otherwise occur between electrolyte and active material
2Reliability
If heat expandable microcapsules are added to prevent thermal runaway, then safety is improved, but device complexity increases
Solution Approach 1:
Heat expandable microcapsules are selectively placed in specific locations within the negative electrode composite material layer, particularly in regions where silicon oxide is present and void formation is most likely. This localized approach provides safety enhancement only where needed, minimizing the overall impact on electrode structure and avoiding uniform complexity throughout the entire electrode
3Object-affected harmful factors
If microcapsules are used to fill voids and prevent electrolyte contact, then thermal runaway is suppressed, but manufacturing precision requirements increase
Solution Approach 1:
The negative electrode composite material layer contains heat expandable microcapsules at a blending ratio of 0.5 mass % or more relative to the total amount of negative electrode active material. This excessive inclusion ensures that sufficient microcapsules are present to fill voids and suppress thermal runaway, compensating for variations in microcapsule distribution and activation during battery operation
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 heat expandable microcapsules effectively fill voids caused by silicon oxide contraction during internal short circuits, preventing electrolyte solution contact with the active material and reliably suppressing temperature rise, thereby enhancing battery safety.
Implementation Method 1
heat expandable microcapsules expand due to the heat generated from an internal short circuit or the like so as to fill the voids resulted from the contraction of silicon oxide
Implementation Method 2
silicon oxide 3 contracts greatly due to quick discharge. Thus, voids are formed in the negative electrode composite material layer
Data Source
AI summary
A negative electrode for a non-aqueous electrolyte secondary battery of the present disclosure includes a negative electrode current collector, a negative electrode composite material layer formed on the surface of the negative electrode current collector. The negative electrode composite material layer includes a negative electrode active material containing silicon oxide and heat expandable microcapsules. The ratio of silicon oxide to the total amount of the negative electrode active material is 30 mass % or less. The blending ratio of the heat expandable microcapsules to the total amount of the negative electrode active material is 0.5 mass % or more. The ratio of the heat expandable microcapsules in contact with silicon oxide to the amount of the heat expandable microcapsules contained in the negative electrode composite material layer is 70 mass % or more.