What is the difference between a nickel-metal hydride battery and a lithium battery?

Rechargeable batteries mainly include lead-acid batteries and alkaline batteries. Currently used nickel-cadmium (NiCd), nickel-hydrogen (NiMH) and lithium-ion (Li-Ion) batteries are alkaline batteries.

The basic structure of the valve-regulated maintenance-free lead-acid battery for lead-acid batteries is shown in Figure 1. It consists of positive and negative plates, separators, electrolytes, safety valves, gas plugs, and outer casings. The active material on the positive electrode plate is lead dioxide (PbO 2 ), and the active material on the negative electrode plate is spongy pure lead (Pb). The electrolyte is prepared from distilled water and pure sulfuric acid in a certain ratio. After a certain density of electrolyte is charged into the battery cell, an electromotive force of about 2.1 V is generated between the positive and negative plates due to the electrochemical reaction.

When using a new lead-acid battery for the first time, it must be fully charged. If charging at a charge rate of 0.1 C, it takes about 55 to 75 hours. After the battery is used normally, it should be charged immediately. Commonly used methods are: (1) grading constant current charging method; (2) low voltage constant voltage charging method (with load charging); (3) fast charging method. The initial charge time of fast charging is less than 5 hours, and the normal charging time can be shortened to about 1 hour.

Nickel-cadmium battery The active material on the positive plate of NiCd battery consists of nickel oxide powder and graphite powder. Graphite does not participate in chemical reaction, and its main function is to enhance conductivity. The active material on the negative electrode plate is composed of cadmium oxide powder and iron oxide powder. The function of the iron oxide powder is to make the cadmium oxide powder have high diffusibility, prevent agglomeration, and increase the capacity of the electrode plate. The active materials are respectively wrapped in the perforated steel strip, and become the positive and negative plates of the battery after press molding. The plates are separated by an alkali-resistant hard rubber insulating rod or a perforated polyvinyl chloride corrugated board. The electrolyte is usually a potassium hydroxide solution. The self-discharge rate of the NiCd battery (ie, the rate at which the battery loses its charge when not in use) is moderate compared to other batteries. When the NiCd battery is in use, if the discharge is not complete, it will be charged again. When it is discharged again, it will not be able to discharge all the power. For example, after releasing 80% of the power and then fully charging, the battery can only emit 80% of the power. This is the so-called memory effect. Of course, several complete discharge/charge cycles will return the NiCd battery to normal operation. Due to the memory effect of the NiCd battery, if it is not completely discharged, each battery should be discharged below 1V before charging.

The nickel-hydrogen battery NiMH battery positive plate material is NiOOH, and the negative electrode plate material is hydrogen absorbing alloy. The electrolyte is usually a 30% aqueous KOH solution with a small amount of NiOH added. The separator is made of a porous vinylon nonwoven fabric or a nylon nonwoven fabric. NiMH batteries are available in both cylindrical and square sizes. The structure of the cylindrical sealed NiMH battery is shown in Figure 2.

Nickel-metal hydride batteries are a good battery. Nickel-metal hydride batteries are classified into high-voltage nickel-hydrogen batteries and low-voltage nickel-hydrogen batteries. The positive electrode active material of the nickel-hydrogen battery is Ni(OH)2 (called NiO electrode), the negative electrode active material is metal hydride, also called hydrogen storage alloy (electrode called hydrogen storage electrode), and the electrolyte is 6 mol/L potassium hydroxide solution. Nickel-hydrogen batteries are increasingly attracting attention as an important direction for hydrogen energy applications.

Since fossil fuels have become less and less in the case of large-scale development and utilization of human beings, the development and utilization of hydrogen energy has received increasing attention in recent years. Nickel-hydrogen batteries have become more and more important as an important direction for hydrogen energy applications. Although nickel-metal hydride batteries are indeed a good performance battery,special nickel-metal hydride batteries are high-voltage nickel-hydrogen batteries (hydrogen pressure up to 3.92 MPa, or 40 kg/cm2) such high-pressure hydrogen is stored in thin-walled containers. It is easy to explode, and nickel-metal hydride batteries also need precious metals as catalysts, making its cost very expensive, which is difficult to accept for civilian use. Therefore, foreign low-voltage nickel-metal hydride batteries have been explored since the 1970s. Nickel-metal hydride batteries are classified into high-voltage nickel-hydrogen batteries and low-voltage nickel-hydrogen batteries. High-voltage nickel-metal hydride batteries were first developed in the early 1970s by M. Klein and J. F. Stockel of the United States. The trend of replacing nickel-hydrogen batteries with nickel-hydrogen batteries and applying them to variousspecials has been formed.

The positive electrode active material of the nickel-hydrogen battery is Ni(OH)2 (called NiO electrode), the negative electrode active material is metal hydride, also called hydrogen storage alloy (electrode called hydrogen storage electrode), and the electrolyte is 6 mol/L potassium hydroxide solution. The process of forming the electrode sheet of the active material mainly includes sintering type, slurry type, foam nickel type, fiber nickel type and inlay type. The electrodes prepared by different processes have large differences in capacity and large current discharge performance. The battery is produced according to a process using different conditions. Most of the consumer batteries such as communication use a slurry-type negative electrode and a foamed nickel-type positive electrode to form a battery. The charge-discharge chemical reaction is as follows [1]:

Positive electrode: Ni(OH)2+OH-=NiOOH+H2O+e-

Negative electrode: M+H2O+e-=MHab+OH-

Total reaction: Ni(OH)2+M=NiOOH+MH

Note: M: hydrogen alloy; Hab: adsorption of hydrogen; the process of the reaction from left to right is the charging process; the process of the reaction from right to left is the discharge process.

Ni(OH)2 and OH- of the positive electrode react to form NiOOH and H2O during charging, and release e- together to form MH and OH-. The total reaction is Ni(OH)2 and M to form NiOOH, hydrogen storage alloy hydrogen storage; discharge In contrast, MHab releases H+, H+ and OH- to form H2O and e-, NiOOH, H2O and e- regenerate Ni(OH)2 and OH-. The standard electromotive force of the battery is 1.319V.

Nickel-metal hydride batteries are classified into high-voltage nickel-hydrogen batteries and low-voltage nickel-hydrogen batteries.

The low-voltage nickel-hydrogen battery has the following characteristics: (1) the battery voltage is 1.2~1.3V, which is equivalent to the cadmium-nickel battery; (2) the energy density is high, 1.5 times or more of the cadmium-nickel battery; (3) the rapid charge and discharge, low temperature Good performance; (4) sealable, strong resistance to overcharge and discharge; (5) no dendritic crystal formation, can prevent short circuit inside the battery; (6) safe and reliable, no pollution to the environment, no memory effect. [1]

The high-voltage nickel-hydrogen battery has the following characteristics: (1) High reliability. It has better over-discharge and over-charge protection, and can withstand high charge and discharge rates and no dendrite formation. Has a good ratio characteristic. Its mass specific capacity is 60A·h/kg, which is five times that of cadmium nickel batteries. (2) The cycle life is long, up to thousands of times. (3) Fully sealed and less maintenance. (4) The low temperature performance is excellent, and the capacity does not change significantly at -10 °C.

NiMH batteries should be maintained during use.

(1) Avoid using the process of charging. Within the cycle life, the use process should not overcharge, because overcharge easily causes the positive and negative electrodes to swell, causing active material shedding and diaphragm damage, conductive network damage and battery ohmic polarization to become larger.

(2) Prevent deterioration of the electrolyte. During the cycle life of Ni-MH batteries, the hydrogen evolution of the battery should be suppressed.

(3) Storage of nickel-metal hydride batteries. The nickel-metal hydride battery should be stored in a fully charged state. If the battery is stored for a long period of time without storing electrical energy in the battery, the function of the battery negative hydrogen storage alloy will be weakened and the battery life will be shortened.

(4) Charging after the battery is exhausted. Nickel-metal hydride batteries and nickel-cadmium batteries have the same "memory effect", that is, if the battery is repeatedly charged while the battery is still in the middle of the discharge, the battery will soon be unavailable.

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