Jul 18, 2019 Pageview:535
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 variousspecials.
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 [1] :
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. [1]
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. As an alternative to the earlier nickel-cadmium batteries, ni-mhbatteries are the most environmentally friendly batteries at present. The toxic cadmium can be eliminated before the heavy metal elements can be used. Nickel-metal hydride batteries have a high energy density ratio, which means that the use of nickel-metal hydride batteries can effectively extend the working time of the equipment without adding extra weight to the digital equipment. Another advantage of nickel-metal hydride batteries is that it greatly reduces the "memory effect" existing in nickel-metal hydride batteries, which makes nickel-metal hydride batteries more convenient to use.
Nimh battery is the most mature secondary battery in the field of HEV. However, from an objective point of view, nickel-metal hydride battery also has some "constraints" : the refining technology is not mature, the cost is too high. There is also a big hidden danger is once the large-scale promotion, the future will face the recycling problem. In the long run, ni-mh battery will face the strong challenge of lithium ion battery, but in the short run, ni-mh battery is still promising in the coming new energy era.
Lithium battery future star
Since its commercialization in 1991, the entire lithium ion battery industry has developed rapidly. Among them, polymer lithium ion battery is superior to liquid lithium ion battery in safety, volume, mass, capacity and discharge performance, with a wider range of applications.
At the 5th Beijing international exhibition of electric vehicles and clean energy vehicles held recently, the reporters found that almost all the pure electric buses that the bus manufacturers brought to the exhibition used lithium batteries. Faw bus USES lithium battery, zhongdaqingshan pure electric bus and shandong yixing use lithium iron phosphate battery, and a variety of lithium batteries including lithium ion phosphate group electron and lithium ion phosphate group have been fully demonstrated.
Song jian, executive vice President of automotive engineering research institute of tsinghua university, said that at present, 99% of the global market share of hybrid battery is ni-mh battery, and the development of ni-mh battery technology in China is relatively mature. But nickel is expensive and nimh batteries cost much more to produce than lithium batteries. Compared with nickel-metal hydride batteries, the new generation of lithium batteries will be reduced by half in weight, the storage capacity will be more than doubled, and the driving range will be greatly improved after a single charge. And the life of nimh batteries will reach its limit in the next three to five years. In the long run, lithium battery will become a more reliable power source for the development of new energy vehicles in the future.
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