The storage of lithium-ion batteries poses certain questions, especially whether should lithium ion batteries be stored fully charged. We will discuss the science behind it and derive practical guidelines.
Basic concepts of charging for lithium-ion batteries
What is lithium battery
Lithium-ion batteries are a type of rechargeable (secondary) battery that mainly relies on the movement of lithium ions between the positive and negative electrodes to work. During the charging and discharging process, Li+ is intercalated and deintercalated between the two electrodes: during charging, Li+ is deintercalated from the positive electrode and embedded into the negative electrode through the electrolyte, making the negative electrode in a lithium-rich state; the process is reversed during discharge.
Lithium-ion batteries have numerous applications, such as:
- Portable Batteries，Power Tool Batteries，Electric Vehicle Batteries，Energy Storage Batteries，High-power Batteries
Several basic units of lithium battery basic concepts
- Nominal Voltage: The potential difference between the positive and negative electrodes of a lithium battery is called the nominal voltage of the lithium battery. The nominal voltage is determined by the electrode potential of the electrode material and the concentration of the internal electrolyte.
- Open-Circuit Voltage: The end voltage of the lithium battery in the open circuit state is called the open circuit voltage. The open circuit voltage of the lithium battery is equal to the difference between the reduction electrode potential of the positive electrode and the electrode potential of the negative electrode.
- Working Voltage: The working voltage refers to the voltage that a lithium battery displays during the discharge process after the load is connected, also known as the discharge voltage. The initial working voltage of a lithium-ion battery during the discharge process is called the initial voltage.
- Storage voltage: The lithium ion storage voltage refers to the voltage when the battery is stored. the storage voltage of lithium batteries should be between 3.7V~3.9V. In addition, lithium batteries should be stored in a cool, dry and ventilated environment, far away from water, fire sources and high temperatures.
- Capacity: The amount of electricity that a lithium battery can provide under certain discharge conditions is called the capacity of the lithium battery, represented by the symbol C. The commonly used unit is ampere-hour. The capacity of a lithium battery is affected by the positive electrode material used, the temperature of the battery, the discharge rate, voltage, etc.
- Cycle Life: The cycle life of a lithium battery is usually represented in terms of usage, with one cycle representing a complete charge and discharge cycle of a lithium battery (i.e., the electricity of a lithium battery is charged from empty to full, and then discharged from full to empty).
Note: Lithium batteries have good cycle characteristics and can generally maintain about 80% of their capacity after 500 cycles.
- Charge/Discharge Rate: The charge rate refers to the current required for a battery to discharge its rated capacity within a specified time. Numerically, it is the multiple of the rated capacity of the battery and is usually represented by the letter C. Generally, 0.2~2C is a capacity lithium battery.
- The discharge rate refers to the size of the current when the lithium battery is discharged. It is generally represented by C and is expressed by the formula: Discharge Rate = Discharge Current / Rated Capacity
- Operating Temperature: The working temperature of a lithium battery refers to the environment and the temperature of the battery itself that it can adapt to while maintaining normal charging and discharging work.
- When a lithium battery is at a low temperature, the discharge platform will decrease to a certain extent. At high temperatures, it will affect the cycle performance of the battery and cause the battery to expand slightly. Therefore, batteries are generally recommended to work within the range of 0-40 degrees Celsius.
what is considered high voltage
The classification of high and low voltage batteries can be considered from two perspectives:
- The voltage of the battery cell can define it.
High-voltage batteries can be divided into high-voltage batteries (4.35V / 4.4V) and ordinary voltage batteries (4.2V) in terms of lithium polymer battery cells. The nominal voltage of an ordinary voltage lithium battery is 3.6 / 3.7V, and the upper limit of the charging voltage is generally 4.2V. The nominal voltage of lithium battery is 3.8V and 3.85V is considered high voltage. The corresponding charge cut-off voltages are 4.35V and 4.4V, respectively.
- The voltage of the battery pack can define high-voltage batteries.
High-voltage battery packs, or high-voltage storage batteries, generally refer to batteries above 48V, and they form a complete set. These types of batteries include high-voltage lead-acid batteries, high-voltage nickel-hydrogen batteries, and high-voltage lithium batteries. What needs to be noted is that they are all achieved by series connection of single cells. The higher the voltage, the more unstable the battery pack composed of single cells. Therefore, the voltage of common high-voltage battery packs is between 48V and 110V.
Whether it's a high-voltage or low-voltage battery pack, each is assembled into a battery pack via series and parallel connection of single cells. Its foundation is low-voltage battery cells that are achieved through series and parallel connections.
Best way to store lithium-ion batteries
- The charging voltage should not exceed the maximum charging voltage, and the discharging voltage should not be lower than the minimum operating voltage.
- At all times, lithium-ion batteries must maintain a voltage above the minimum operating voltage. Over-discharge or self-discharge at low voltage may lead to the decomposition and damage of the active lithium-ion material, and it may not necessarily be reducible.
- Any form of overcharge of lithium-ion batteries will cause severe damage to the battery performance, and may even cause explosions. Lithium-ion batteries must be prevented from being overcharged during the charging process.
- Avoid frequently conducting deep discharges and deep charges. However, after about 30 charging cycles, the power detection chip will automatically perform a deep discharge and deep charge once to accurately assess the battery status.
- Avoid high temperatures, as it can shorten the battery life and in severe cases can lead to an explosion. If possible, it can be stored in a refrigerator. If the laptop is using AC power, please remove the lithium-ion battery to avoid being affected by the heat generated by the computer.
- Avoid freezing, but the freezing point of the electrolyte solution in most lithium-ion batteries is -40°C, so it is not easy to freeze.
- If you do not use it for a long time, please store it at a charge of 40% to 60%. When the power is too low, it may cause over-discharge due to self-discharge.
- Since lithium-ion batteries will also naturally age when not in use, therefore, when purchasing, you should choose based on the actual demand, and it is not appropriate to buy too much.
Are there the best battery brand of lithium battery to ignore the above battery preservation and use guidelines
Indeed, there's no absolute best battery brand of lithium battery can perfectly adapt to every scenario. However, you can select the most suitable battery brand based on your use scenario.
For instance, Epoch Lithium Battery is a brand that specializes in lithium batteries. Their products are primarily aimed towards small, portable electronic devices, including but not limited to smartphones, laptops, cameras, and drones.
Icon Lithium Battery mainly serves scenarios involving motorcycle or electric bicycle batteries. Their products are designed to handle intense vibrations and harsh weather conditions, making them especially suitable for such vehicles.
While both these brands have been in the lithium-ion battery manufacturing industry for many years, it can't be said that their batteries are the absolute best as they can't satisfy all battery needs. It's also crucial to adhere to the storage and usage guidelines proposed earlier.
Conclusion: How to store lithium-ion batteries
Lithium-ion batteries should not be fully charged during storage.
In reality self-discharge is a phenomenon that exists in lithium-ion batteries. If the battery voltage is stored below 3.6V for a long time, it can lead to over-discharge of the battery, which damages the internal structure of the battery and reduces its lifespan. Therefore, lithium-ion batteries stored for a long time should be recharged every 3 to 6 months, that is, charging to a voltage of 3.8 to 3.9V (the best storage voltage for lithium-ion batteries is around 3.85V). It is not recommended to fully charge the battery.