Silicon Negative Electrode Crystallite Size Control
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Solution Overview
Problem
Conventional lithium secondary batteries using silicon as the negative electrode active material face challenges in achieving high energy density and maintaining cycle performance due to expansion and shrinkage, leading to deterioration and increased battery thickness.
Innovation Solution
The use of silicon or silicon alloy particles with a crystallite size of 100 nm or less, having a cleavage plane in the (111) plane, which fractures along this plane during charge and discharge, preventing extensive surface exposure and reaction with the electrolyte, thereby improving cycle performance and preventing thickness increase.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If silicon particles are used as negative electrode active material to achieve high energy density, then battery capacity increases, but cycle performance deteriorates due to expansion and shrinkage causing surface exposure and electrolyte reaction
Solution Approach 1:
The silicon particles are segmented into multiple crystallites with sizes of 100 nm or less within each particle. This segmentation prevents catastrophic fracture during expansion and shrinkage, as the smaller crystallites can accommodate volume changes independently, reducing surface exposure and electrolyte reaction, thereby maintaining cycle performance while preserving high capacity
Solution Approach 2:
The crystallite size parameter is changed to 100 nm or less, which fundamentally alters the mechanical behavior of silicon during lithiation and delithiation. This parameter change enables the material to withstand repeated expansion and shrinkage cycles without catastrophic failure, resolving the contradiction between high capacity and cycle performance
2Quantity of substance
If silicon particles are used as negative electrode active material to achieve high energy density, then battery capacity increases, but battery thickness increases due to expansion
Solution Approach 1:
Segmenting silicon into small crystallites (100 nm or less) allows the material to expand and shrink in a more controlled manner. The segmented structure accommodates volume changes with less overall expansion compared to large monocrystalline silicon, thereby preventing excessive battery thickness increase while maintaining high capacity
Solution Approach 2:
Changing the crystallite size to 100 nm or less modifies the expansion behavior of silicon during charging. The smaller crystallite size enables more efficient volume accommodation, reducing the net expansion and preventing excessive battery thickness increase while preserving the high capacity benefits of silicon
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 approach enhances the cycle performance and prevents battery thickness increase by controlling the crystallite size of silicon or silicon alloy particles, ensuring uniform reaction and improved adhesion, leading to better charge-discharge characteristics.
Implementation Method 1
the negative electrode active material particles include silicon particles and/or silicon alloy particles having a crystallite size of 100 nm or less; the single crystal of the silicon/silicon alloy particles has a cleavage plane in the (111) plane, and therefore, the expansion and shrinkage of the negative electrode active material during the charge and discharge causes the particles to fracture along the cleavage plane
Implementation Method 2
When silicon is used as the negative electrode active material, however, the negative electrode active material undergoes expansion and shrinkage, and consequently, each time the charge and discharge are performed
Data Source
AI summary
[Problem] An object of the invention is to provide a lithium secondary battery that shows good cycle performance and at the same time prevents a battery thickness increase due to charge-discharge cycles, and a method of manufacturing such a battery.[Means for Solving the Problem] A lithium secondary battery includes a negative electrode (2) having a negative electrode current collector (11) and a negative electrode active material layer (12) disposed on the negative electrode current collector (11), a positive electrode (1) having a positive electrode active material, a separator (3), and a non-aqueous electrolyte. The negative electrode active material layer includes negative electrode active material particles and a negative electrode binder, and the negative electrode active material particles include silicon particles and/or silicon alloy particles. The silicon particles and the silicon alloy particles have a crystallite size of 100 nm or less.