Nickel-metal hydride (NiMH) batteries and lithium-ion batteries are both widely used in the market. They are both pollution-free and environmentally friendly batteries, representing important areas of new energy development. So, which is better, NiMH or lithium-ion batteries?
Nickel-metal hydride (NiMH) batteries are currently the primary choice for hybrid electric vehicles (HEVs) due to their mature technology and good safety profile, but they struggle to meet the demands for higher levels of electrification. The current dominance of NiMH batteries stems primarily from the fact that existing hybrid vehicles have battery capacities of only 1-2 kWh, insufficient for pure electric driving or offering a pure electric range of less than 3 km. In the longer term, NiMH batteries are unsuitable for use in PHEVs and EVs, mainly because:
Nickel-metal hydride (NiMH) batteries cannot meet the specific energy and energy density requirements of PHEVs and EVs; the raw material Ni(OH) is expensive, which will increase the cost of manufacturing high-energy batteries; and the technology of NiMH batteries is basically mature, leaving very limited room for improvement in battery performance and reduction in cost.
Like nickel-cadmium (NiCd) batteries, nickel-metal hydride (NiMH) batteries also have a memory effect, but it is much smaller than that of NiCd batteries. Therefore, it is unnecessary to discharge the battery after every charge (as improper operation can damage the battery); a full charge-discharge cycle every three months is sufficient to mitigate the memory effect. NiMH batteries have a self-discharge rate of 25-35% per month, while lithium-ion batteries have a self-discharge rate of 2-5% per month. NiMH batteries have a high self-discharge rate, while lithium-ion batteries have an extremely low self-discharge rate.
Currently, nickel-metal hydride (NiMH) batteries typically have a capacity of up to 2900 mAh (milliampere-hour, commonly referred to as mAh in mainland China). After prolonged periods of non-use, they may leak slightly corrosive and harmful liquids (which can be harmful to humans or damage the device using the battery). Lithium-ion batteries, on the other hand, may burn or explode if not used properly. Relatively speaking, NiMH batteries are considered the safest type of battery.
Nickel-metal hydride (NiMH) batteries have a voltage of 1.2V, while lithium-ion batteries have a voltage of 3.7V. Lithium-ion batteries offer better discharge performance. NiMH batteries cause less environmental pollution, mainly producing acidic and alkaline waste gases. The most harmful component is HCl. With proper environmental protection measures, there should be no problem.
Compared with nickel-metal hydride batteries, the advantages of lithium-ion batteries are mainly reflected in:
1. High specific energy and energy density, approximately twice that of nickel-metal hydride batteries, significantly improving the driving range of electric vehicles; higher power, lower self-discharge, and no memory effect, all of which enhance the ease of use of electric vehicles;
2. Low raw material costs;
3. There is significant room for technological improvement and cost reduction.
4. Size: Rechargeable lithium batteries are widely used in many new mobile devices due to their advantages over ordinary nickel-cadmium/nickel-metal hydride batteries, including smaller size (relatively), lighter weight, lower self-discharge rate, and no memory effect. The batteries in our everyday mobile phones, laptops, PDAs, and other mobile devices have been gradually replaced by lithium batteries.
Nickel-metal hydride batteries don't have a very noticeable memory effect, though there is a slight one. When you need to use them urgently, you don't necessarily need to fully discharge them before recharging; however, for normal use, it's best to fully discharge them before fully charging.
5. Capacity: Lithium batteries have high energy density and are compact; the voltage of a single lithium battery is three times that of a nickel-metal hydride battery; they have no memory effect and can be charged whenever needed. However, they should not be charged after only a short period of use, as excessive charge-discharge cycles will affect battery life. Lithium batteries are not suitable for long-term storage, as they will permanently lose some capacity over time. It is best to charge them to 40% and then store them in the refrigerator.
6. Charging Method: The charging requirements for lithium batteries differ from those for nickel-cadmium/nickel-metal hydride batteries. A single rechargeable lithium battery cell has a voltage of 3.6V (some battery packs may be labeled as single-cell lithium batteries). Lithium batteries are generally charged using a voltage-limiting and current-limiting method. If you wish to charge a lithium battery independently, be aware that its charging method differs from the constant-current charging method used for nickel-cadmium/nickel-metal hydride batteries; you cannot use a standard nickel-cadmium/nickel-metal hydride battery charger.
Although nickel-metal hydride (NiMH) batteries and lithium batteries are different, they are both new-era energy batteries that have played an irreplaceable role in the progress of human life! Objectively speaking, when weight is a key factor affecting product performance and battery maintenance can be done in a timely manner, lithium batteries are the obvious choice. However, when high power, good safety, high reliability, and economic practicality are required, NiMH batteries have more advantages.
In lithium batteries, regardless of the type of lithium-ion battery, a battery protection board is required, which integrates functions such as overcurrent protection, overvoltage protection, and over-discharge protection. Furthermore, prolonged exposure of lithium-ion batteries to high temperatures can lead to irreversible capacity loss, a factor that must be considered when calculating project costs and ensuring project safety.
