The difference between NiMH, NiCd and Lithium batteries

Nickel-metal hydride battery Nickel Metal hydride battery is a combination of hydrogen ions and nickel metal. It has 30% more power reserve than nickel-cadmium battery, is lighter than nickel-cadmium battery, has a longer service life, is environmentally friendly, and has no memory effect. The disadvantage of nickel-metal hydride battery is that it is much more expensive than nickel-cadmium battery and has worse performance than lithium battery. Lithium-ion battery A high energy density battery made of lithium-ion battery. Lithium-ion battery is also a smart battery. It can be used with a dedicated original smart charger to achieve the shortest charging time, the longest life cycle and the largest capacity. Lithium-ion battery is currently the best performing battery. Compared with nickel-cadmium battery and nickel-metal hydride battery of the same size, it has the largest power reserve, the lightest weight, the longest life, the shortest charging time, and no memory effect.

There are two main types of rechargeable batteries: lead-acid batteries and alkaline batteries. Currently used nickel-cadmium (NiCd), nickel-metal hydride (NiMH) and lithium-ion (Li-Ion) batteries are all alkaline batteries.

The positive plate material of nickel-metal hydride batteries NiMH batteries is NiOOH, and the negative plate material is a hydrogen-absorbing alloy. The electrolyte is usually a 30% KOH aqueous solution with a small amount of NiOH added. The diaphragm is made of porous vinylon non-woven fabric or nylon non-woven fabric. NiMH batteries are available in cylindrical and square shapes.
NiMH batteries have good low-temperature discharge characteristics. Even at an ambient temperature of -20°C, the amount of electricity discharged can reach more than 85% of the nominal capacity when discharged with a large current (at a discharge rate of 1C). However, when NiMH batteries are at high temperatures (above +40°C), the storage capacity will drop by 5-10%. This capacity loss caused by self-discharge (the higher the temperature, the greater the self-discharge rate) is reversible, and the maximum capacity can be restored after several charge and discharge cycles. The open circuit voltage of NiMH batteries is 1.2V, the same as that of NiCd batteries.

The charging process of NiCd/NiMH batteries is very similar, and both require constant current charging. The difference between the two is mainly in the termination detection method of fast charging to prevent the battery from overcharging. The charger charges the battery with constant current and detects the battery voltage and other parameters at the same time. When the battery voltage slowly rises to a peak value, the fast charging of NiMH batteries is terminated, while the fast charging of NiCd batteries is terminated when the battery voltage drops by -△V for the first time. To avoid damaging the battery, fast charging cannot be started when the battery temperature is too low. When the battery temperature Tmin is lower than 10℃, it should be switched to trickle charging mode. Once the battery temperature reaches the specified value, charging must be stopped immediately. The active material on the positive plate of the nickel-cadmium battery NiCd battery is composed of nickel oxide powder and graphite powder. Graphite does not participate in chemical reactions, and its main function is to enhance conductivity. The active material on the negative plate is composed of cadmium oxide powder and iron oxide powder. The function of iron oxide powder is to make the cadmium oxide powder have higher diffusivity, prevent agglomeration, and increase the capacity of the plate. The active materials are wrapped in perforated steel strips and pressed into shape to form the positive and negative plates of the battery. The plates are separated by alkali-resistant hard rubber insulating sticks or perforated polyvinyl chloride corrugated boards. The electrolyte is usually potassium hydroxide solution. Compared with other batteries, the self-discharge rate of NiCd batteries (that is, the rate at which the battery loses charge when not in use) is moderate. During the use of NiCd batteries, if they are charged again after not being fully discharged, they will not be able to discharge all the electricity the next time they are discharged. For example, after 80% of the electricity is discharged and then fully charged, the battery can only discharge 80% of the electricity. This is the so-called memory effect. Of course, several complete discharge/charge cycles will restore the NiCd battery to normal operation. Due to the memory effect of NiCd batteries, if they are not fully discharged, each battery should be discharged to less than 1V before charging.