Why can't lithium batteries be stored fully charged? What is the correct storage method?

The core reason why lithium batteries should not be stored fully charged is that when fully charged, the battery is continuously subjected to high-voltage stress. This stress can cause irreversible damage to the electrode materials and electrolyte, ultimately significantly shortening the battery's cycle life and even creating safety hazards.

When fully charged, a large number of lithium atoms in the positive electrode will be extracted and migrate to the negative electrode, resulting in the positive electrode material being in a high oxidation state. Its crystal structure stability decreases sharply, and maintaining this state for a long time will directly cause the positive electrode particles to crack and pulverize, leading to permanent capacity decay. At the same time, the lithium insertion amount in the negative electrode is close to saturation when fully charged. If the storage environment temperature is high, lithium ions are prone to precipitate on the surface of the negative electrode, forming needle-like lithium dendrites. These lithium dendrites will continue to grow and may eventually pierce the internal separator of the battery, causing an internal short circuit, leading to battery bulging, overheating, and in severe cases, even a fire risk. In addition, the high voltage when fully charged will accelerate the oxidation and decomposition of the electrolyte. The gases and impurities produced by decomposition will increase the battery's internal resistance, further exacerbating capacity decay and bulging problems.

The optimal storage solution for lithium batteries focuses on stabilizing the battery's chemical state and slowing down internal reaction rates. Specifically, the following key points should be considered: First, strictly control the stored charge. Mainstream lithium batteries, such as ternary lithium and lithium iron phosphate batteries, are best stored in a medium charge range of 40% to 60%. Within this range, the electrode chemical state is most stable, preventing stress damage from high voltage and avoiding negative electrode passivation caused by a charge level below 20%, which would affect subsequent charge and discharge performance. If the battery is to be stored for an extended period, it is recommended to charge it to approximately 50% before disconnecting it for storage. Never store batteries at a low charge level (<20%) for extended periods.

Storage temperature is also a crucial factor. The ideal environment is a dry, room-temperature space between 0°C and 25°C. High temperatures (>35°C) will drastically accelerate internal chemical reactions, causing rapid capacity decay; while low temperatures below 0°C, although temporarily slowing the reaction, will temporarily increase the battery's internal resistance and may damage the electrolyte, making them unsuitable for long-term storage. Considering that lithium batteries exhibit slight self-discharge even in dormant mode, it is recommended to proactively check the remaining charge every 1-3 months for devices such as electric vehicles and spare batteries that are stored for extended periods. If the charge level drops below 40%, it should be replenished to the 40%-60% range before continuing storage.

When storing, also pay attention to the following: keep the environment dry and avoid moisture or corrosive gases; prevent the battery from being squeezed, bumped, or subjected to other physical damage; never disassemble the battery or modify the protection circuit yourself, as this may damage the battery's safety protection mechanism and cause safety risks.