Are Lithium-ion Power Banks Safe?

To understand the safety hazards of power banks, we must first delve into their core – the world of lithium-ion batteries. From mobile phones and laptops to power banks, the battery life of modern electronic devices relies on this intricate yet energy-intensive device. Its creation was a revolution in battery technology, but its inherent characteristics also sowed the seeds of risk.

1. The Three Core Components of Lithium-ion Batteries

The structure of a lithium-ion battery is not complex. Its core consists of three parts: the positive electrode, the negative electrode, and the electrolyte, along with a separator and casing, forming a closed "energy cycle system."

The positive electrode is the "reservoir" for lithium ions, playing a crucial role in storing and releasing them. Currently, the two most common positive electrode materials on the market are lithium cobalt oxide and lithium iron phosphate. Lithium cobalt oxide has a higher energy density, allowing power banks to be smaller and lighter, and is therefore widely used in consumer electronics; however, its thermal stability is relatively poor, and it is prone to decomposition under high temperatures or abnormal conditions. Lithium iron phosphate (LFP) materials, on the other hand, exhibit extremely high thermal stability and a higher safety factor, but have lower energy density and require a larger volume for the same capacity. They are primarily used in applications with extremely high safety requirements, such as new energy vehicles and large-scale energy storage devices.

The negative electrode, the "temporary residence" for lithium ions, is mainly made of graphite. Graphite has a layered structure, like neatly arranged "cells." During charging, lithium ions can easily embed themselves in these "cells" for storage; during discharging, they can orderly detach from the "cells" and return to the positive electrode. However, if the charging method is improper, lithium ions can abnormally deposit on the graphite surface, forming dendritic lithium metal crystals, or "dendrites," which pose a significant safety risk.

The electrolyte, the "shuttle channel" for lithium ions, is usually an organic solvent, such as carbonate compounds. Its function is to allow lithium ions to move freely between the positive and negative electrodes, completing the conversion of electrical energy into chemical energy. However, this organic solvent is highly flammable. Once exposed to high temperatures or open flames, it will burn rapidly and may even decompose to produce large amounts of flammable gases. This is a key reason why lithium batteries burn so intensely.

Furthermore, inside the battery is a separator only micrometers thick, acting as a "firewall" between the positive and negative electrodes, preventing direct contact. The separator is typically made of polypropylene or polyethylene, with a microporous structure that allows lithium ions to pass through but blocks electrons. However, this "firewall" is very fragile and can lose its insulating function if subjected to physical damage or high temperatures.

2. Energy Density: A Double-Edged Sword of Convenience and Risk

The core advantage of lithium-ion batteries as the preferred power source for modern electronic devices lies in their ultra-high energy density-the ability to store far more electrical energy per unit volume or weight than traditional batteries. For example, a palm-sized power bank can have a capacity of 10,000mAh, enough to charge a mobile phone 2-3 times, while a nickel-cadmium battery of the same capacity can be more than three times larger and heavier.

The convenience brought by this high energy density is self-evident: there's no need to carry bulky power banks when going out; power banks can easily be slipped into a backpack or pocket, allowing you to replenish your devices anytime, anywhere. However, the more concentrated the energy, the higher the risk. Like explosives, a small amount of explosive is relatively safe, but if highly concentrated, even a small spark can trigger a violent explosion. The high energy density of lithium-ion batteries essentially compresses a large amount of chemical energy into a small space. Once this chemical energy is accidentally triggered, it will be released at an extremely rapid rate, creating an uncontrollable disaster.

3. Battery Management System (BMS): A Safe "Smart Manager"

Reputable manufacturers' lithium battery power banks are equipped with a Battery Management System (BMS), which acts as the power bank's "smart manager," monitoring and protecting the battery's operating status.

The core functions of the BMS include overcharge protection, over-discharge protection, short-circuit protection, and over-temperature protection. During charging, when the battery is fully charged, the BMS automatically cuts off the charging circuit to prevent excessive lithium ions from embedding into the negative electrode. During discharging, when the charge level falls below a safe threshold, it stops discharging to prevent the positive electrode material structure from collapsing. If a short circuit is detected between the positive and negative electrodes, it immediately cuts off the current. When the battery temperature exceeds the safe range, it initiates a cooling program or stops operating.

The high risk of substandard power banks is largely due to the omission of a BMS or the use of a very poor-quality BMS. Without the monitoring of this "smart manager," the battery is like a runaway horse; once an anomaly occurs, protective measures cannot be taken in time, easily leading to thermal runaway.

ACEY-BMS-1 BMS Tester Machine is used in the safety test of lithium battery protection board, to detect whether the functional indicators of the protection board are within the reasonable parameters, to provide a set of testing standards to the staff, which is conducive to improving production efficiency and facilitating quality control.

The spontaneous combustion and explosion of lithium-ion battery power banks are essentially chain reactions triggered by "thermal runaway." Thermal runaway refers to the continuous accumulation of heat inside the battery, causing the temperature to rise continuously, which in turn triggers a series of exothermic reactions, ultimately leading to an irreversible combustion and explosion process. This process typically lasts only a few seconds to tens of seconds, is extremely fast, and is difficult to interrupt manually.

1. Internal Short Circuit: A "Time Bomb" Hidden Inside the Battery

Internal short circuits are one of the main causes of thermal runaway, referring to the direct contact between the positive and negative electrodes of the battery through internal impurities or dendrites, forming a current loop.

The formation of internal short circuits mainly has two causes: First, defects in the manufacturing process. If impurities such as metal debris are mixed into the positive electrode, negative electrode, or separator during battery production, these impurities may become "bridges" between the positive and negative electrodes, leading to a short circuit. Second, dendrites formed during long-term use. During charging, lithium ions embed themselves into the layered structure of the graphite in the negative electrode. However, if the charging current is too high, the number of charging cycles is too numerous, or an incompatible charger is used, some lithium ions will fail to embed successfully and instead deposit on the surface of the negative electrode, forming dendritic lithium metal crystals (dendritices). Over time, these dendrites grow and eventually pierce the micron-sized separator, connecting the positive and negative electrodes and causing a short circuit.

Once an internal short circuit occurs, a huge current is instantly generated inside the battery. According to Joule's law, current flowing through a resistor generates a large amount of heat. Within seconds, the internal temperature of the battery can soar to hundreds of degrees Celsius. This high temperature causes the electrolyte to burn rapidly, decomposing into flammable gases such as hydrogen and carbon monoxide. The internal pressure of the battery increases dramatically, eventually causing the casing to rupture. The leaking gases mix with air and, upon contact with the high temperature, ignite a deflagration.

In a 2024 incident involving a certain brand of power bank spontaneously combusting, testing revealed that the presence of metallic impurities inside the battery, after prolonged use, caused an internal short circuit, leading to thermal runaway.

2. External Short Circuit: The Most Easily Overlooked Risk in Daily Use

An external short circuit occurs when the positive and negative terminals of a battery are directly connected through an external metal object, forming a current loop and instantly generating high temperatures.

The causes of external short circuits are very common, mostly stemming from poor usage habits. For example, placing a power bank in the same pocket or backpack compartment as keys, coins, or data cables can cause these metal objects to accidentally come into contact with the power bank's positive and negative terminals, creating a short circuit. The risk is even higher for power banks without protective covers on the ports-the sharp end of a key can easily insert into the port, simultaneously contacting the positive and negative metal contacts.

Furthermore, damaged power bank ports or broken data cable insulation can also lead to external short circuits. For example, exposed metal wires in a data cable can come into contact with the power bank port, potentially causing a short circuit. The high temperatures generated by an external short circuit can directly ignite the power bank casing or surrounding flammable materials, potentially causing a fire.

In 2023, a college student placed a power bank and keys in the side pocket of his backpack. While walking, the keys accidentally jammed the power bank's port, causing an external short circuit. A few minutes later, the backpack began to smoke. Fortunately, it was discovered in time and extinguished with a fire extinguisher, preventing serious consequences.

3. Overcharging and Over-discharging: Hidden Dangers of Improper Charging Habits

Overcharging and over-discharging refer to a battery exceeding its rated capacity during charging or falling below its minimum safe capacity during discharging. Both situations damage the battery structure and can lead to thermal runaway.

Overcharging is particularly dangerous. When a battery is fully charged, if charging continues, excessive lithium ions are forcibly embedded in the graphite of the negative electrode, causing the graphite's layered structure to collapse and rupture. Simultaneously, excess lithium ions precipitate metallic lithium on the surface of the negative electrode, reacting violently with the electrolyte and releasing a large amount of heat. Furthermore, overcharging can increase the internal pressure of the battery, causing the separator to shrink or even rupture, leading to a short circuit between the positive and negative electrodes.

The main cause of overcharging is the use of inferior or incompatible chargers. For example, using a charger with excessively high output current to charge a power bank, or using a substandard charger without overcharge protection. Some users habitually charge their power banks overnight. Although a legitimate power bank's BMS will disconnect the power when fully charged, a malfunctioning BMS or a poor-quality charger can lead to overcharging.

Over-discharging is equally dangerous. When a battery is over-discharged, the crystal structure of the positive electrode material undergoes irreversible damage, leading to a decrease in battery capacity and the generation of a large amount of heat and unstable substances. Leaving a power bank completely depleted and idle for extended periods can trigger the risk of over-discharge.

4. High-Temperature Environments: A Catalyst for Accelerated Risk Explosions

High temperatures are the "enemy" of lithium batteries, significantly increasing the probability of thermal runaway. High-temperature environments accelerate internal chemical side reactions, reduce the stability of the separator, and make the electrolyte more prone to decomposition and gas generation.

High-temperature environments are common in daily life: Windowsills exposed to direct sunlight in summer can reach temperatures exceeding 50°C; the interior of a car parked outdoors can even exceed 60°C; placing a power bank near heat sources like radiators or microwaves will also cause its temperature to rise.

In high-temperature environments, the chemical reactions inside the battery accelerate significantly, and the movement of lithium ions becomes abnormally vigorous, easily leading to dendrite growth and separator damage. Simultaneously, the flammability of the electrolyte increases with temperature, and it will ignite immediately upon contact with even a tiny spark or the high temperature generated by a short circuit.

In the summer of 2024, a car owner placed a power bank on the dashboard inside their car. After half a day of exposure to direct sunlight, the power bank exploded, shattering the car window. Testing revealed that the temperature inside the car reached 65°C, far exceeding the safe operating temperature of the power bank (generally 0°C-45°C).

5. The Entire Chain Reaction Process of Thermal Runaway

Once thermal runaway is triggered, it forms an irreversible chain reaction. The entire process can be divided into four stages:

Stage 1: Heat Accumulation. Whether it's an internal short circuit, external short circuit, overcharging/over-discharging, or a high-temperature environment, all will cause the battery's internal temperature to rise. At this time, the battery may exhibit slight overheating, bulging, etc., which are warning signs of thermal runaway.

Stage 2: Electrolyte Combustion. When the temperature reaches the electrolyte's flash point (usually between 130℃ and 200℃), the electrolyte will begin to burn, releasing a large amount of heat and flammable gas. The battery temperature will surge rapidly to over 500℃.

Stage 3: Pressure Explosion. Flammable gas continuously accumulates inside the sealed battery casing, and the pressure continues to increase. When the pressure exceeds the casing's tolerance limit, the casing will rupture, and the gas will be ejected instantaneously.

Stage 4: Deflagration and Propagation. When the ejected flammable gas mixes thoroughly with air, it will violently explode upon encountering the high temperatures inside the battery or an open flame, producing a large amount of smoke and flames. The flame temperature can reach over 1000℃, and toxic gases are produced during the combustion process, making it extremely dangerous.

The risks of lithium battery power banks are not unavoidable. By mastering scientific usage methods, these risks can be effectively reduced. From selection and use to storage and maintenance, each step has clear safety boundaries. Adhering to these boundaries ensures that the power bank remains a safe "energy block."

1. Selection: Eliminating Risks at the Source

Selection is the first and most crucial step for safe use. Substandard power banks harbor safety hazards from the very beginning of their production.

• Look for 3C certification. 3C certification is a mandatory product certification in China. As electrical products, power banks must pass 3C certification to be sold on the market. When purchasing, check for a clear and valid 3C certification mark on the power bank's casing. The mark should include the certification number, manufacturer information, etc. Never buy products without a 3C mark, with a blurred mark, or those that have been recalled.
• Choose reputable brands. Prioritize purchasing power banks from well-known brands such as Huawei, Xiaomi, Apple, and Ugreen, as these brands have more standardized manufacturing processes. Also prioritize purchasing power banks using batteries from leading companies like ATI, EVE Energy, Changhong Energy, and Zijian Electronics, as these manufacturers strictly control raw material quality and equip their products with comprehensive BMS systems. Avoid purchasing "three-no" products (products without manufacturer's name, address, or production date), as these are usually cheap, use inferior batteries and rudimentary manufacturing processes, and offer no safety guarantees.

• Pay attention to capacity and specifications. Choose a power bank with a capacity appropriate for your needs. Generally, a 10000mAh-20000mAh power bank is sufficient for daily travel. Also, check the product specifications to ensure the output voltage and current match your electronic devices to avoid charging abnormalities due to mismatches.

• Inspect the appearance and workmanship. When purchasing, carefully check whether the power bank's casing is smooth and undamaged, whether the interfaces are secure and not loose, and whether the buttons are responsive. If the casing has obvious burrs, gaps, or loose interfaces, it indicates poor workmanship and is not recommended for purchase.

2. Usage: Develop Good Habits

Correct usage habits are key to avoiding risks. Many safety accidents stem from improper usage.

• Use original or qualified accessories. When charging, use the original charger and data cable from the power bank, or choose accessories from reputable brands that match the power bank's specifications. Avoid using inferior data cables or universal chargers, as these may have unstable current or damaged insulation, easily leading to overcharging or short circuits.

• Avoid overcharging and over-discharging. Do not charge the power bank overnight. It is recommended to unplug the power source promptly after the battery is fully charged. During daily use, do not wait until the power bank is completely depleted before recharging. It is recommended to recharge when the battery level is between 20% and 30% to avoid over-discharge.

• Keep away from extreme environments. Avoid using the power bank in high-temperature, low-temperature, or humid environments. Do not use or charge it in direct sunlight, in hot cars, or in bathrooms. In low-temperature environments, battery capacity will decrease; do not force charging in such conditions to avoid damaging the battery.

• Prevent physical damage. During use, avoid physical damage to the power bank, such as dropping, squeezing, puncturing, or bending. Do not place the power bank under heavy objects, do not disassemble it, and do not puncture the power bank's casing with sharp objects.

• Promptly handle abnormal situations. If you notice the power bank becoming hot, bulging, smoking, or emitting an unusual odor during use, stop using it immediately, unplug it, and place it in an open, non-flammable place to cool naturally. Do not use it again.

3. Storage and Maintenance: Extending Lifespan + Reducing Risk

Proper storage and maintenance not only extend the lifespan of the power bank but also further reduce safety risks.

• Maintain a suitable storage environment. Power banks not used for extended periods should be stored in a dry, ventilated, and cool place, with the temperature maintained between 10℃ and 30℃. Do not store power banks with flammable, explosive, or metal objects to avoid short circuits or fires.

• Recharge the power bank regularly. If the power bank is not used for an extended period, it is recommended to top up the charge every 1-2 months, maintaining it at around 50%-70%. This effectively protects the battery and prevents over-discharge that could damage it.

• Regularly check its condition. Regularly inspect the power bank's appearance, ports, and cables. If you find any damage to the casing, loose ports, or aging cables, stop using it immediately and contact the manufacturer for repair or replacement.

• Do not modify it yourself. Never disassemble or modify the power bank to achieve higher capacity or faster charging speeds. Modifications will damage the battery structure and BMS, significantly increasing safety risks.

The invention of lithium battery power banks has greatly facilitated our lives, freeing us from the anxiety of running out of power while traveling, working, or studying. However, behind this convenience lies a profound respect for safety boundaries. It is both a "power source" in our hands and a potential "powder keg." The key lies in whether we can understand its safety protocols and adhere to the safety boundaries of its use.

ACEY-MLW-200T Laser Spot Welding Machine applied of tab welding for power banks and mobile power supply.

Contact now