The “Invisible Guardian” of Lithium Battery Safety: The Diaphragm.

Schematic diagram of battery thermal runaway causes：

Recently, a storm has been set off in the mobile power industry - brands such as Anker Innovations and ROMOSS have recalled more than 1.2 million power banks, involving three ROMOSS models (such as PAC20-272, PAC20-392, and PLT20A-152), with a recall of up to 490,000 units. The reason behind this? Lithium battery safety hazards! The announcement mentioned "battery raw material defects" and "diaphragm insulation failure", but for ordinary users, these terms are confusing. But in fact, the problem stems from the core component of lithium batteries: the diaphragm. When this thin guardian fails, it may turn from a protector to a "trigger point", causing internal short circuits, bloating and even combustion in the battery. As the key to lithium battery safety, the failure mechanism of the diaphragm is complex - for example, melting and shrinking at high temperatures (PE materials soften at 135°C) or pore blockage triggers electrolyte decomposition, producing gases such as CO₂ and H₂. This recall storm exposed the defect that low-cost diaphragms are prone to aging during circulation.

In the lithium battery safety system, the role of the diaphragm seems simple: physically isolating the positive and negative electrodes to prevent short circuits. But it is also the "invisible guardian" of lithium batteries. If the diaphragm material is improperly selected (such as using low-grade PE materials), or the process is out of control (impurities remain or tension is uneven), a chain reaction may be triggered. Imagine that during the charging and discharging of the lithium battery, if the diaphragm is corroded by electrolyte byproducts, the pore blockage aggravates the uneven ion transmission, and eventually causes lithium precipitation, dendrite growth, and even micro-short circuits. This is not only applicable to lithium batteries for mobile power supplies, but is also crucial in the field of energy storage batteries - whether it is a home outdoor power supply or large-scale grid storage, the lack of safety will lead to disasters.

Looking deeper, diaphragm failure is the "Achilles' heel" of lithium battery safety. This risk is particularly prominent in lithium iron phosphate batteries (lithium iron phosphate batteries are widely used in electric vehicles and renewable energy fields) because although their chemical composition is stable, diaphragm defects such as residual impurities (metals such as Fe and Cu) or moisture corrosion can still catalyze side reactions and accelerate gas production. For energy storage battery systems, diaphragm problems may be magnified - the long-term operation of energy storage solutions depends on high-durability lithium batteries. For example, if the diaphragm used in energy storage batteries has insufficient thermal stability (below 200°C), it is easy to shrink in high temperature environments (such as commercial PE softens at 135°C), causing positive and negative short circuits and Joule heating. This may lead to the collapse of the entire energy storage solution.

But hope is not far away! The industry is strengthening the safety of lithium batteries through innovative materials and technologies. For example, the use of ceramic coating (Al₂O₃/SiO₂) separators can improve heat resistance to more than 200°C, or aramid separators can withstand high temperatures of 300°C. Structural optimization (such as double-sided PVDF coating) and process control (tension balance at 5–10 N) can also reduce injection wrinkles and pore blockage. These improvements not only protect lithium batteries in mobile power supplies, but also pave the way for safety for lithium iron phosphate batteries and energy storage batteries. In energy storage solutions, optimizing the separator means a more reliable lithium battery life - through high temperature resistant design and strict Gurley value control (maintained at 300–500 s/100mL), the risk of flatulence can be significantly suppressed to ensure the smooth operation of the energy storage system.

In short, the safety issue of lithium batteries is not only about the recall storm. Every bulge is a reminder of the role of the diaphragm as a "guardian". Through material modification and process optimization, lithium batteries can improve safety from the source - whether it is the application of lithium iron phosphate batteries in distributed storage, or the integration of energy storage batteries into smart grid energy storage solutions. After all, in the future dominated by lithium batteries, the safety of each battery depends on the protection of this micron-thick diaphragm. Let us embrace technological innovation and create a safer lithium battery world.