Jun 25, 2019 Pageview：25
Nickel metal hydride battery is a kind of battery with good performance. Nickel-metal hydride batteries are divided into high voltage nickel-metal hydride batteries and low voltage nickel-metal hydride batteries. The positive active material of nickel hydrogen battery is Ni (OH) 2 (NiO electrode), the negative active material is metal hydride, also known as hydrogen storage alloy (electrode is called hydrogen storage electrode), and the electrolyte is 6mol/L potassium hydroxide solution. As an important direction of hydrogen energy application, nickel-metal hydride batteries are attracting more and more attention.
In recent years, more and more attention has been paid to the development and utilization of hydrogen energy because the fossil fuels are less and less in the large-scale development and utilization of human beings. As an important direction of hydrogen energy application, nickel-metal hydride batteries are attracting more and more attention. Although nimh batteries is indeed a good battery performance, but the space with nickel metal hydride batteries are the nimh batteries (hydrogen pressure of 3.92 MPa, 40 kg/cm2), such as high pressure hydrogen storage in the thin wall container used easily, and the nimh batteries need noble metal catalyst, make it become very expensive, the cost of it is acceptable for civil, therefore, abroad since the 70 s began to explore civil low-voltage nimh batteries. Nickel-metal hydride batteries are divided into high voltage nickel-metal hydride batteries and low voltage nickel-metal hydride batteries. High pressure nickel metal hydride battery was first developed by m.k. lein and j.f. stokkel in the United States in the early 1970s. Nickel-metal hydride (nimh) batteries are replacing cdni batteries and are being used on various satellites.
The positive active material of nickel hydrogen battery is Ni (OH) 2 (NiO electrode), the negative active material is metal hydride, also known as hydrogen storage alloy (electrode is called hydrogen storage electrode), and the electrolyte is 6mol/L potassium hydroxide solution. The process of active material forming electrode sheet mainly includes sintering type, pulping type, foam nickel type, fiber nickel type and infiltration type, etc. There are great differences in capacity and large current discharge performance of electrodes prepared by different processes. Generally, batteries are produced by different processes according to different operating conditions. Communication and other civil batteries are mostly composed of pulp-type negative electrode and nickel-foam positive electrode. Charge-discharge chemical reactions are as follows  :
Positive electrode: Ni (OH) 2+OH-=NiOOH+H2O+e-
Negative: M + H2O + e = MHab + OH -
Total reaction: Ni (OH) 2+M=NiOOH+MH
Note: M: hydrogen alloy; Hab: adsorbed hydrogen; The reaction equation from left to right is the process of charging; The reaction equation from right to left is the process of discharge.
When charging, Ni (OH) 2 and OH- in the positive electrode react to form NiOOH and H2O, and at the same time release e- to form MH and OH- together. On the contrary, MHab releases H+, H+ and OH- to form H2O and e-, and NiOOH, H2O and e- to form Ni (OH) 2 and OH-. The standard electromotive force of the battery is 1.319V. 
Nickel-metal hydride batteries are divided into high voltage nickel-metal hydride batteries and low voltage nickel-metal hydride batteries.
The low-voltage nickel-metal hydride battery has the following characteristics :(1) the battery voltage is 1.2~1.3V, which is similar to that of cadmium nickel battery; (2) high energy density, more than 1.5 times higher than that of cadmium nickel battery; (3) it can be charged and discharged quickly with good performance at low temperature; (4) it can be sealed and has strong resistance to overcharge and discharge; (5) no dendritic crystal formation can prevent short circuit in the battery; (6) safe and reliable environment without pollution, no memory effect. 
High - voltage nickel - hydrogen batteries have the following characteristics :(1) strong reliability. It has better over discharge and over charge protection, can bear high charge and discharge rate and no dendrite formation. Has good specific characteristics. Its mass ratio capacity is 60A·h/kg, which is 5 times higher than that of cadmium nickel battery. (2) long cycle life, up to thousands of times. (3) full sealing, less maintenance. (4) the low temperature performance is good, in - 10 ℃, the capacity has no apparent change. 
Nimh batteries should be maintained when in use.
(1) avoid overcharging during use. During the cycle life, overcharge should be avoided in the use process. This is because overcharge is likely to cause the positive and negative electrodes to expand, causing the active matter to fall off and the diaphragm to be damaged, damaging the conductive network and increasing the ohmic polarization of the battery.
(2) prevent electrolyte deterioration. During the cycle life of nickel metal hydride batteries, hydrogen evolution should be inhibited.
(3) storage of nimh batteries. Nickel metal hydride battery storage should be in full power, if there is no power storage in the battery to preserve the battery for a long time, will make the battery cathode hydrogen storage alloy function weakened, and lead to short battery life.
(4) charge after the power is exhausted. Nickel-metal hydride batteries and nickel-cadmium batteries are the same, have a "memory effect", that is, if the battery is still in the state of residual electrical energy during the discharge of repeated charging use, the battery will not be used soon
Nickel-metal hydride batteries have become a mature product. At present, the number of nickel-metal hydride batteries produced in the international market last year is about 700 million. The scale and output of Japan's nickel-metal hydride battery industry has always been among the highest in the world. China is rich in rare earth metals, which are the raw materials of nickel metal hydride batteries. At present domestic research and development of nickel hydrogen battery raw material processing technology is becoming mature. Nickel-metal hydride batteries can be used interchangeably with zn-mn batteries and cd-ni batteries. In the future, circular batteries are mainly developed towards the diversity and commercialization of product specifications, while square batteries are mainly developed as the power source of vehicles. 
The operating voltage of nimh and nicad batteries is 1.2v. But nimh has a higher volume to energy ratio than nicd cells. According to the different factors of the process of making batteries, nickel-cadmium batteries have strong memory effect, while nickel-hydrogen batteries have little memory effect. Nickel-cadmium batteries, meanwhile, contain the heavy metal cadmium, which has been banned. However, ni-mh batteries cannot replace ni-cd batteries in many power tools due to their excellent discharge performance at high rates. So in the ROSH standard nickel-cadmium batteries are temporarily allowed to be used in power tools.
Difference between lithium battery and nickel metal hydride battery:
At the same volume, lithium battery has a larger capacity than nimh battery, so its talk time and standby time are longer than nimh battery, and its price is higher than nimh battery. Also, in general, nimh batteries can not be used with charge, greatly reduced convenience.
The development of lithium ion battery is first lithium battery, then lithium ion battery. Early lithium batteries used pure lithium wafers for the negative electrode. This kind of lithium can easily catch fire and cause danger. On this basis, lithium ion batteries are developed. The cathode of a lithium-ion battery is graphite. Ions conduct lithium ions, not lithium metal. Security is greatly improved.
The working voltage of lithium ion battery is 3.7v. Higher volume than nimh. At present, lithium ion battery has aluminum shell, steel shell and flexible packaging. Market share in their respective areas. Some markets are common, such as lithium batteries for mobile phones.
However, since the operating voltage of the previous disposable battery and nimh battery was 1.2-1.5v, the two tandem batteries were 2.4v ~ 3.0v. Most of the electrical appliances have set this working voltage standard. Such as walkman, radio, etc. Therefore, in the civilian battery, lithium battery can not replace nimh battery. However, in the later development of new electrical appliances, such as MP3,MP4, etc., lithium battery as a mobile power supply.
Therefore, ni-mh, ni-cd and li-ion batteries cannot be replaced by other batteries in their respective fields.
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