Nickel-metal hydride (NiMH) batteries and lithium-ion batteries are both widely used in the market. They are both environmentally friendly, pollution-free batteries and important areas for the development of new energy sources. So, which is better, NiMH or lithium-ion batteries?
The difference between lithium-ion batteries and nickel-metal hydride batteries
Structurally, nickel-metal hydride batteries use Ni(OH) as the positive electrode and a metal hydride as the negative electrode, with a 6 mol/L potassium hydroxide solution as the electrolyte. Lithium-ion batteries, on the other hand, embed lithium ions into petroleum coke and graphite to form the negative electrode. Common positive electrode materials include LixCoO2, LixNiO2, or LixMnO4. The electrolyte composition is more complex, consisting of a mixture of LiPF6, diethylene carbonate, and dimethyl carbonate in specific proportions.
Nickel-metal hydride (NiMH) batteries are an important choice for hybrid electric vehicles (HEVs) due to their mature technology and good safety, but they are difficult to meet the requirements for higher levels of electrification. The main reason why lithium-ion batteries currently dominate the market is that the battery energy of existing hybrid vehicles is only 1-2 kWh, which is not enough for pure electric driving or has a pure electric range of less than 3 km.
In the longer term, nickel-metal hydride (NiMH) batteries cannot be used in PHEVs and EVs. This is mainly because the specific energy and energy density of NiMH batteries cannot meet the requirements of PHEVs and EVs; the raw material Ni(OH) is expensive, which would increase the cost of manufacturing high-energy batteries; and NiMH battery technology is basically mature, leaving very limited room for improvement in battery performance and cost reduction.
Like nickel-metal hydride (NiMH) batteries, nickel-cadmium (NiCd) batteries also have a memory effect, but it is much smaller than that of NiCd batteries. Therefore, it is not necessary to discharge the battery with every charge (as improper operation can damage the battery). A full charge and discharge cycle every three months is sufficient to mitigate the memory effect.
Nickel-metal hydride (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 my country). 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, have the potential to burn or explode if not used properly. Relatively speaking, NiMH batteries are considered the safest type of battery.
Nickel-metal hydride batteries have a voltage of 1.2V, while lithium-ion batteries have a voltage of 3.7V. Lithium-ion batteries have better discharge performance.
Nickel-metal hydride batteries have relatively low environmental pollution, mainly consisting of some acidic and alkaline waste gases. The most harmful component is HCl. If environmental protection measures are in place, there should be no problem.
Compared to nickel-metal hydride batteries, lithium-ion batteries have several key advantages:
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-ion 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 gradually been replaced by lithium-ion 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-ion batteries have high energy density and are compact; the voltage of a single lithium-ion 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 too frequently after each use, as excessive charge-discharge cycles will affect battery life. Lithium-ion 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-ion batteries differ from those for nickel-cadmium/nickel-metal hydride batteries. A single rechargeable lithium-ion battery cell has a voltage of 3.6V (some battery packs may be labeled as single-cell lithium-ion batteries). Lithium-ion batteries are generally charged using a voltage-limiting and current-limiting method. If you wish to charge a lithium-ion 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-ion batteries differ, they are both new-era energy batteries that play an irreplaceable role in advancing human life. Objectively speaking, when weight is a key factor affecting product performance and timely battery maintenance is possible, using lithium-ion batteries is the obvious choice. However, when high power, safety, reliability, and cost-effectiveness are required, NiMH batteries have a greater advantage.
