The main performance requirements for lithium battery separators currently include four major performance indicators: thickness uniformity, mechanical properties (including tensile strength and puncture resistance), air permeability, and physicochemical properties (including wettability, chemical stability, thermal stability, and safety).
The technological development of lithium battery separators has been driven by changes in the application of lithium-ion batteries. Currently, the prominent feature is the trend of lithium batteries becoming smaller and larger, and lithium batteries becoming larger and larger.
Let's look at it from a "small" perspective.
This is primarily reflected in lithium batteries used in portable consumer electronics, such as mobile phones, digital cameras, and electronic dictionaries. The aesthetic and miniaturization requirements of lithium battery design necessitate increasingly thinner separators for these applications. High energy density means accommodating more electrode material in a smaller volume. Given fixed positive and negative electrode materials, superior separator performance becomes essential. This necessitates maintaining the original battery capacity and cycle life while achieving thinner separators.
Looking at it from a broader perspective
This is mainly reflected in the lithium-ion batteries used in electric bicycles and electric vehicles. The numerous electric vehicle fires reported in China clearly demonstrate that safety performance is currently the bottleneck restricting the use of lithium-ion batteries. The main reasons for this are threefold:
1. Safety is the core of the physical and chemical properties of lithium-ion battery separators; any defect in any of the other three properties can lead to unstable safety performance.
2. The larger the capacity of a single lithium-ion battery cell, the fewer cells need to be connected in series. This objectively requires the use of larger capacity cells in power lithium-ion batteries. The larger the capacity, the more refined the manufacturing process is needed to ensure the performance of the cells.
3. Due to the safety hazards brought about by the consistency and combination technology of series-connected cells, the manufacturing of lithium battery separators needs to be more precise.
The superior performance of lithium batteries and lithium battery packs cannot solely rely on individual separators; comprehensive matching of the positive and negative electrodes and electrolyte components is essential to achieve this goal. Lithium battery packs also present complex assembly technology challenges. However, separator technology, as the most valuable lithium battery technology, is undeniably crucial.
