Lithium-ion batteries should not be stored at full charge. The primary reason is that, in a fully charged state, the battery's interior is subjected to continuous high-voltage stress. This stress inflicts irreversible damage upon the electrode materials and electrolyte, ultimately drastically shortening the battery's cycle life and potentially creating latent safety hazards.
When fully charged, a large number of lithium atoms deintercalate from the positive electrode and migrate to the negative electrode. This leaves the positive electrode material in a highly oxidized state, causing a sharp decline in the stability of its crystal lattice structure. Maintaining this state over extended periods directly leads to the cracking and pulverization of positive electrode particles, triggering a permanent decline in battery capacity. Concurrently, when fully charged, the lithium intercalation level at the negative electrode approaches saturation. If the storage environment temperature is elevated, lithium ions are prone to precipitating on the negative electrode surface, forming needle-like lithium dendrites. These dendrites continue to grow and may eventually puncture the internal separator, triggering an internal short circuit. This, in turn, leads to battery swelling and overheating, and in severe cases, poses a significant risk of fire. Furthermore, the high voltage associated with a fully charged state accelerates the oxidative decomposition of the electrolyte; the gases and impurities generated by this decomposition increase the battery's internal resistance, thereby further exacerbating capacity degradation and swelling issues.
The optimal strategy for storing lithium-ion batteries centers on stabilizing their chemical state and slowing down internal reaction rates. Specifically, the following key guidelines should be observed:
First and foremost, strictly control the charge level during storage. Mainstream lithium-ion battery types-such as ternary lithium and lithium iron phosphate (LiFePO4)-are best stored within a moderate charge range of 40% to 60%. Within this range, the chemical state of the electrodes is most stable; this prevents stress-induced damage caused by high voltage while simultaneously avoiding negative electrode passivation which can impair subsequent charging and discharging performance-that typically occurs when the charge level drops below 20%.
If a battery is to remain idle for an extended period, it is recommended to first charge it to approximately 50% before disconnecting the power and storing it; under no circumstances should a battery be stored for long periods in a low-charge state (below 20%).
Storage temperature is another critical factor; the ideal environment is a cool, dry space maintained at a temperature between 0°C and 25°C. High temperatures (above 35°C) drastically accelerate internal chemical reactions within the battery, leading to rapid capacity degradation. Conversely, while low temperatures (below 0°C) may temporarily slow down these reactions, they cause a temporary increase in the battery's internal resistance and can potentially damage the electrolyte, making such conditions unsuitable for long-term storage.
Given that lithium batteries experience a slight degree of self-discharge even when in a dormant state, it is recommended that for devices intended for long-term storage-such as electric vehicles or backup battery systems-the remaining charge level be actively checked once every 1 to 3 months. If the charge level drops below 40%, it should be promptly recharged to a range of 40% to 60% before resuming storage.
Additional precautions for storage include: maintaining a dry environment to prevent damage from moisture or corrosive gases; protecting the battery from physical damage such as crushing or impact; and strictly refraining from unauthorized disassembly of the battery or modification of its protection circuitry, as doing so may compromise the battery's safety mechanisms and create significant safety hazards.
