What is the difference between nickel-cadmium battery and nickel-hydrogen battery?

What is the difference between nickel-cadmium battery and nickel-hydrogen battery?

Difference between rechargeable battery and ordinary battery: besides difference terminal voltages,there are still two differences: First, internal resistance of rechargeable battery is much lower than that of ordinary battery, such as measuring a section number 5 with a digital multimeter. The short-circuit current of ordinary batteries is generally below 3A, and the short-circuit current of a No. 5 nickel-cadmium or nickel-hydrogen battery is generally above 4A. It is because of this that we are judging true and false nickel-cadmium and nickel-hydrogen. When charging battery, you can use a digital meter to measure its instantaneous short-circuit current to distinguish. Second, discharge characteristics of nickel-cadmium and nickel-hydrogen rechargeable batteries are different from those of ordinary batteries, especially when discharge terminated. In discharge process of ordinary batteries, terminal voltage gradually reduced by 1.5V with increase of discharge amount, and there is no sudden change of the terminal voltage, while nickel-cadmium and nickel-hydrogen batteries are different, during tdischarge process. The terminal voltage hardly changes with the amount of discharge, but once the discharge is completed. Terminal voltage reduced from about 1.2V to about 1.0V, and the discharge current reduced by a factor of two. Continued discharge at a voltage drop of 1.0 V or less called overdischarge, which is harmful to the battery and affects the life.

The rechargeable batteries we use today generally classified into four categories according to their chemical composition: nickel-cadmium batteries (NiCd), nickel-hydrogen batteries (NiMH), lead-acid batteries (PbSO4), and lithium-ion batteries (Li+). ). Here is a brief introduction to these four types of rechargeable batteries:

(1) Lead-acid battery: It a kind of rechargeable battery that appeared earlier, which is a common car battery. There are two types of ordinary lead-acid batteries and valve-pull sealed lead-acid batteries. The former gradually replaced by the latter due to inconvenient use and serious environmental pollution. The emergency lights we use are generally such batteries, with a normal cycle life of 1000 to 1200 times.

(2) Nickel-cadmium battery: It is also an early battery. That is, the portable battery that is commonly used by people at present. The nominal voltage of a single battery is 1.25V, and its capacity (the capacity of the rechargeable battery is expressed by the current (mA) multiplied by the hour (h). If the capacity of a battery is 500MA, it means that the battery can discharge at a current of 500MA. Hour) For the general 5th battery (AA type) between 450 and 800MA, the normal cycle charging frequency is more than 500 times, but if it is used incorrectly, it will greatly shorten the number of uses. Nickel-cadmium batteries have a phenomenon called "memory effect". When people charge a nickel-cadmium battery that has not been discharged, the battery automatically "records" a point that is not fully discharged. When the next charge reaches this point, it will exhibit the same characteristics as the battery discharged. In this way, although the battery has not completely discharged, the capacity reduced at the same time. This is the so-called "memory effect". The essence is that a dendritic crystal structure generated in the electrode. This "memory effect" is unique to the nickel-cadmium battery. Of. It will seriously affect the capacity of the battery and reduce the battery life. Therefore, nickel cadmium should completely discharged before the battery charged, so that it can recharged after the discharge, and you should not repeat it when using this battery. Charging the battery, most of the commercially available chargers that are automatically charged will have a small charging current. The battery will fully charged for at least 15 hours, and the battery will not fully discharged. Some chargers with better functions will enter the pre-processing stage when they confirmed to be able to charge quickly. At this stage, the charger completely discharges the battery, so that each battery completely discharged, so that the voltage of each battery drops to about 1.0v. To eliminate the "memory effect" of nickel-cadmium batteries. After pretreatment of the nickel-cadmium battery, it directly enters the fast charging phase, and after the rapid charging completed, it transferred to the trickle charging, and the time required is generally 2-3 hours.

(3) Nickel-metal hydride battery: It is a newly developed rechargeable battery with similar performance to nickel-cadmium battery, but its energy density is higher. The capacity of a No. 5 Ni-MH battery is between 1000mah and 1300mah. In addition, it does not have a "memory effect" and it has no pollution to the environment. Therefore, some people call it "green battery" and certainly, the price is a little high.

(4) Lithium-ion battery: It is also a recently developed battery. The biggest advantage is that the energy density is higher, but its price is also very high. It generally used in high-end electronic products, but it should not exceed the discharge voltage during discharge. Moreover, it cannot be greater than the discharge current discharge.

In order, properly use all kinds of rechargeable batteries, it is very important fully charge the battery for the service life of the battery. If the charging method is not correct, the battery life will greatly shortened.

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 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 charged into the battery cell, an electromotive force of about 2.1 V 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 fully charge. If charging at a charge rate of 0.1 C, it takes about 55 to 75 hours. After the battery used normally, it should charge 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 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 infusibility, prevent agglomeration, and increase the capacity of the electrode plate. Active materials wrapped in perforated steel strip and become positive, negative plates of battery. The plates 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 charged again. When it 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 not completely discharged, each battery should 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 shown in Figure 2.

NiMH battery accelerates forward

As an alternative to the early nickel-cadmium battery, Ni-MHBatteries are the most environmentally friendly batteries, eliminating the use of toxic cadmium and eliminating the environmental pollution caused by heavy metals. NiMH batteries have a large energy density ratio, which means that nickel-hydrogen batteries can effectively extend the operating time of equipment without adding extra weight to digital equipment. Another advantage of nickel-metal hydride batteries is that they greatly reduce the "memory effect" present in nickel-cadmium batteries, which makes nickel-hydrogen batteries more convenient to use.

Why do nickel-metal hydride batteries replace the most favored lithium batteries? In fact, it makes no sense. First, nickel-metal hydride batteries have been on the market since the 1990s, and have tested for a longer period. Secondly, nickel-hydrogen mineral resources are sufficient; once again, there are many domestic manufacturers, and there more than 100 private enterprises that make nickel-hydrogen batteries in Guangdong alone. Fourth, compared with lithium batteries, nickel-metal hydride batteries characterized by high safety and not easy to explode. .

Nickel-metal hydride batteries are currently the most mature secondary batteries in the HEV automotive field. However, objectively, there are also some "depressions" in nickel-metal hydride batteries: the refining technology is not mature enough and the cost is too high. There is also a big hidden danger that once it is widely promoted, it will face the problem of recycling in the future. In the end, nickel-metal hydride batteries will face the strong challenge of lithium-ion batteries, but in the short term, nickel-metal hydride batteries are still promising in the upcoming new energy era.

Lithium- battery future star

Since the commercialization in 1991, the entire lithium-ion battery industry has developed rapidly. Among them, polymer lithium-ion batteries are superior to liquid lithium-ion batteries in terms of safety, volume, quality, capacity and discharge performance, and have a wider application range.

At the fifth Beijing International Electric Vehicle Clean Energy Vehicle Exhibition held recently, the reporter found that almost all of the pure electric buses exhibited by the major bus manufacturers used lithium batteries. FAW Bus uses lithium-powered batteries, Zhongda Qingshan pure electric bus, Shandong Haoxing adopts lithium -iron phosphate battery, and a variety of lithium batteries including phosphoric acid-based lithium ion electrons and lithium lanthanum phosphate have been fully demonstrated.

Song Jian, executive vice president of the Automotive Engineering Research Institute of Tsinghua University, said that 99% of global market share for hybrid battery is nickel-metal hydride batteries, and development of nickel-hydrogen battery technology in China is mature. However, price of nickel is expensive, and nickel-hydrogen battery is much higher in production cost than lithium battery. Compared with nickel-metal hydride batteries, weight of new-generation lithium battery will reduced by half, and storage capacity will more than doubled. Mileage will greatly improve after one charge. Moreover, life of nickel-metal hydride batteries will reach its limit in the next three to five years. In the end, lithium batteries will become a more powerful source of power for development of new energy vehicles in the future.

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