Research on a common lithium-ion cathode has found that repeated charging to the upper end of its range creates mechanical stress and lasting microcracks, while heat can accelerate the damage.
Keeping a smartphone battery at 100% for long periods can shorten its useful life, according to research from the University of Warsaw and the Warsaw University of Technology published in the journal Small Structures. The study focused on NMC622, a common cathode material used in lithium-ion batteries, and found that pushing the cell to full charge increases mechanical stress inside the material. That stress does not vanish when the battery is discharged; instead, it leaves behind damage that accumulates over time.
The researchers tracked what happens inside the cathode as lithium ions move in and out of the structure during charging and use. In NMC622, those ions sit between layers of oxygen and metal atoms, and repeated cycling changes the spacing within the crystal lattice. At high states of charge, the movement became uneven across the electrode surface, and the layers began to bend, twist and shift. The scientists used X-ray methods, electron microscopy and light-scattering analysis to observe the process directly.
The most serious harm appeared when the battery was charged to the upper end of its range. After around 50 cycles at 4.3 volts, cracks began forming along grain boundaries. When the voltage rose to 4.7 volts, the damage spread into the grains themselves. Some of the structural distortion was reversible once the lithium returned, but the microcracks remained and gradually reduced the cathode’s ability to store and release current. Polish reports on the study described the effect as irreversible wear to the battery material.
The practical lesson is less dramatic than the headline suggests, but still important. Experts quoted by TechRadar said charging to 100% occasionally is not a problem, because modern batteries and phones include safety margins and charge-management systems. The greater risk comes from making full charging a routine and from heat, which can accelerate chemical ageing even more quickly than high voltage alone. For that reason, many specialists recommend keeping day-to-day charging within roughly 20% to 80% where possible, using adaptive charging if the phone offers it, and avoiding conditions that make the device hot.
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