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after the official launch of the iphone 16, disassembly reports from all sides also began as expected, and many bloggers discovered that the iphone 16 pro used a battery with a steel casing.

combined with the recent high heat of the lebanese incident, a large number of conspiracy theories about the iphone 16 battery have appeared on the internet. some people believe that the steel shell battery will seal the internal heat and pressure in the battery for a longer time, and the accumulated pressure will make the explosion more violent; others believe that the steel shell of the battery may produce more dangerous fragments in the explosion, becoming "shrapnel" that hurts people...

but that is clearly not the case.

full metal jacket or full metal bomb

before discussing the controversy over steel-cased batteries, we need to understand the possibility of mobile phone explosions and the reasons behind them.

lithium batteries are the only components in mobile phones with high energy density. due to their high chemical activity and the susceptibility to short circuits, thermal runaway and other problems during the charging and discharging process, they are the components most likely to cause explosions.

in contrast, other components of mobile phones do not involve energy storage or complex chemical reactions, and the risk is relatively small. a large number of mobile phone explosion cases also further prove that battery problems are the main cause of explosions.

in addition to factors such as external damage, overcharging or over-discharging, in general, the short circuit of lithium batteries is caused by the uneven deposition of lithium ions on the negative electrode during the charging and discharging process, forming lithium dendrites.

these slender lithium metal structures extend like branches, slowly accumulate, and may eventually pierce the separator inside the battery. the separator is the only physical barrier between the positive and negative electrodes. once pierced by lithium dendrites, the positive and negative electrodes are in direct contact, causing abnormal discharge inside the battery.

as a large current passes through the battery, the battery generates a lot of heat, which cannot be dissipated in time and can only accumulate inside the battery, causing the internal temperature to rise sharply. as the temperature rises, the chemical reaction inside the battery becomes extremely active, and the chemicals begin to decompose and release more heat and combustible gases.

the battery structure begins to expand due to the accumulation of gas and heat, which is manifested externally as a bulging battery. if this process continues, the physical strength of the battery shell will gradually be unable to withstand the internal pressure, which may eventually cause the battery to rupture or even burn. this series of processes is the thermal runaway phenomenon caused by a short circuit.

in order to deal with possible problems, apple has taken several "insurance" measures for the safety of the steel shell battery of the iphone 16. the physical properties of steel materials are stable, and the pressure resistance is much higher than other materials such as aluminum. it can prevent the battery from deforming or cracking to the greatest extent. even if there is a problem, it is difficult to break into a large number of fragments directly as some netizens speculate.

the newly added "pressure relief valve" design can release excess pressure immediately when the pressure inside the battery increases, reducing the thermal runaway phenomenon caused by short circuit. since thermal runaway of lithium batteries requires a process, even if danger really occurs, it can leave people a certain amount of reaction time.

although the cause of the lebanon explosion remains inconclusive, the energy of the battery alone is unlikely to cause such a huge force. many people suspect that there was a problem with the production chain of the equipment or that it was "tampered with" during transportation.

such things may still happen in the fields of bp machines and walkie-talkies where the production chain is unclear and the brand authorization is confusing, but for mobile phones with a clear production chain and tight structure, it may be extremely difficult to modify any link in the process.

as we all know, most of the iphone 16 production lines are in china. in order to achieve standardization as much as possible, its production process has been highly transparent. from component procurement, production and assembly to transportation and sales, each link is subject to strict monitoring and review; in order to maximize the use of internal space, the layout of the iphone has been carefully designed. during the assembly process, some dust may affect the final effect, not to mention the situation of stuffing dozens of grams of high explosives.

in addition, at this year's apple conference, we also saw apple's protection measures at the software level. the iphone 16 has a built-in intelligent battery management system. by monitoring the battery's temperature, voltage, and current in real time, it can promptly trigger the power protection mechanism when an abnormality is detected, further reducing the possibility of overheating and short circuits. the person in charge of the relevant mobile phone manufacturer said:

4g and 5g mobile phones have a lot of privacy and security policies at the communication level, operating system level, application level, and battery management level. in addition, at the battery management level, if the phone gets hot, for example, over 80 degrees, it will be hard shut down. hardware sensors plus hardware switches can achieve hard shutdown, which is not software logic and cannot be hacked by hackers.

steel-shell batteries can be found everywhere

in fact, steel-shell batteries are widely used. currently, most laptop batteries, new energy vehicle batteries and daily household batteries are steel-shelled: tesla's 4680 battery shell uses a nickel-plated stainless steel shell of about 635μm.

most of the no. 5 and no. 7 batteries used in daily household use also use stainless steel thin shells; steel-shell button batteries have become standard for many wearable devices and small electronic products.

if we simply associate steel shells with explosions and believe that steel shell batteries will turn into "fragmentation grenades" when they explode, we are obviously ignoring the reality that we are already surrounded by steel shell batteries.

this is not the first time that apple has used steel-cased batteries. techinsights discovered that apple used metal-cased batteries on apple watch during a disassembly in 2019. in the same year, apple applied for a patent for a metal-cased battery, which showed that there was an isolation layer between the metal casing and the battery. the metal casing could be connected to a common ground, allowing other components to contact the metal casing without short circuiting, and optimizing the available space of the device by reducing the spacing between the battery casing and other components.

techinsights compared the apple watch series 7 battery with a larger version of the battery, showing that the steel-cased battery reduced the coverage area by about 10% without reducing the capacity per unit area. the 41mm version of the watch has a larger battery because it uses a steel-cased battery.

ming-chi kuo previously revealed that the new battery density will increase by 5-10%. blogger @楼斌robin also disassembled the iphone 16 pro and found that the battery capacity is 3582mah, an increase of 308mah compared to the previous generation. it uses atl batteries, and its internal batteries basically fill the entire space. the energy density reaches 764wh/l, which is a significant improvement over the previous generation. obviously, the metal shell battery used in the iphone 16 pro is likely to be the technology used in previous watches, and its safety has been verified by time.

in addition to the improvement in product experience brought by the steel shell itself, apple's change of shell this time is largely due to the influence of "external forces".

in 2023, the eu passed the eu batteries and waste batteries regulation, requiring that batteries in all household appliances and consumer electronics should be easily removable and replaceable to improve product repairability and reduce electronic waste.

during the disassembly, we can also see that in order to improve "repairability", apple has also improved the bonding technology between the battery and the motherboard for some models of the iphone 16 series.

ifixit found that using a 20v voltage can debond the iphone 16 battery in 5 seconds, which is much more convenient than the previous generation. at 5v voltage, it only takes a little more than 6 minutes, which is equivalent to using another battery to complete the iphone 16 battery disassembly.

the related technology public paper "unraveling the mechanism of electrically induced adhesive debonding: a spectro-microscopic study" introduces:

when electricity is applied, the molecular chains in this new adhesive will rearrange themselves, thereby enhancing its adhesion ability, and under the action of the electric field, the self-healing process can be completed faster, further improving the durability and reusability of the material.

obviously, the introduction of this material is to improve the repairability of the iphone battery, making it the most repairable generation of iphone in history.

not only has the adhesive been upgraded, but apple has also specially processed the grooves of the frame to create a rough surface in order to increase the contact area of ​​the adhesive for better performance. in the microscope close-up of evident scientific, we can see that the craftsmanship is very beautiful.

however, some disassembly bloggers pointed out that currently only the iphone 16 pro uses a stainless steel shell, and the iphone 16&plus still uses an aluminum-plastic soft-pack battery, which requires us to mention some of the shortcomings of stainless steel batteries.

stainless steel casings are stronger, more durable, and more impact-resistant than aluminum alloys, but they are also heavier. according to the dismantler, the iphone 16 pro is 7.1g heavier than the previous generation. aluminum alloy is not only lighter, but also relatively inexpensive, so it is often used in standard iphones to control production costs and attract a wider user base.

the stronger corrosion resistance and hardness of the stainless steel casing also means higher processing costs. apple's favoritism this time may be based on cost and cost-effectiveness considerations.

electronic products are indispensable in modern life, and it cannot be overemphasized that we should pay attention to product safety. however, whether from the perspective of materials, technical principles, maturity, strict supervision, or management of the production chain, we can see that changing the material of the battery casing will not turn the mobile phone into a "bomb" as the rumors say.

more importantly, even if we don’t use the iphone 16 pro, we are still exposed to a variety of products that use steel shell batteries every moment.

perhaps it is because our trust has been consumed too much that the lebanon incident has become a "trigger point" for public sentiment.