Nickel metal hydride ni mh battery. All about Ni-MH batteries: device, characteristics, pros and cons

The main difference between Ni-Cd batteries and Ni-Mh batteries is their composition. The base of the battery is the same - it is nickel, it is the cathode, and the anodes are different. For a Ni-Cd battery, the anode is metal cadmium, for a Ni-Mh battery, the anode is a hydrogen metal hydride electrode.

Each type of battery has its pros and cons, knowing them, you can more accurately select the battery you need.

Will the old charger fit the new battery if I change from Ni-Cd to Ni-Mh or vice versa?

The principle of charging for both batteries is exactly the same, so the charger can be used from the previous battery. The basic rule for charging these batteries is that they can only be charged after they have been completely discharged. This requirement is due to the fact that both types of batteries are subject to the "memory effect", although with Ni-Mh batteries this problem is minimized.

How to properly store Ni-Cd and Ni-Mh batteries?

The best place to store the battery is in a cool dry place, as the higher the storage temperature, the faster the battery will self-discharge. The battery can be stored in any condition other than full discharge or full charge. The optimal charge is 40-60 %%. Once every 2-3 months, additional charge should be carried out (due to the self-discharge present), discharge and again charge up to 40-60 %% of the capacity. Storage for up to five years is acceptable. After storage, the battery should be discharged, recharged and then used normally.

Can I use batteries with a larger or smaller capacity than the original set?

Battery capacity is the amount of time your power tool has been running on battery power. Accordingly, for a power tool, there is absolutely no difference in battery capacity. The actual difference will only be in the charging time of the battery and the operating time of the power tool on battery power. When choosing a battery capacity, you should start from your requirements, if you need to work longer using one battery - the choice is in favor of more capacious batteries, if the complete batteries are completely satisfactory, then you should stay on batteries of equal or similar capacity.

Nimh batteries are power supplies that are classified as alkaline batteries. They are similar to nickel-hydrogen batteries. But the level of their energy capacity is higher.

The internal composition of ni mh batteries is similar to that of nickel-cadmium power supplies. To prepare a positive conclusion, such a chemical element, nickel, is used, a negative one - an alloy that includes absorbing type hydrogen metals.

There are several typical designs of nickel metal hydride batteries:

• Cylinder. To separate the conductive leads, a separator is used, which is given the shape of the cylinder. An emergency valve is concentrated on the cover, which opens slightly when the pressure rises significantly.
• Prism. In such a nickel metal hydride battery, the electrodes are concentrated alternately. A separator is used to separate them. To accommodate the main elements, a body made of plastic or a special alloy is used. To control the pressure, a valve or a sensor is introduced into the cover.

Among the advantages of such a power source are:

• Specific energy parameters of the power source increase during operation.
• No cadmium is used in the preparation of conductive elements. Therefore, there are no problems with battery disposal.
• Lack of a kind of "memory effect". Therefore, there is no need to increase the capacity.
• In order to cope with the discharge voltage (reduce it), specialists discharge the unit to 1 V 1-2 times a month.

Among the restrictions that are related to nickel metal hydride batteries, there are:

• Compliance with the established range of operating currents. Exceeding these indicators leads to a rapid discharge.
• Operation of this type of power supply in severe frosts is not allowed.
• Thermal fuses are introduced into the battery, with the help of which the overheating of the unit is determined, the temperature rise to a critical indicator.
• Self-discharge tendency.

Charging the NiMH battery

The charging process of nickel metal hydride batteries is associated with certain chemical reactions. For their normal flow, part of the energy is required, which is supplied by the charger, from the network.

The efficiency of the charging process is the part of the energy received by the power supply that is stored. The value of this indicator may vary. But at the same time, it is impossible to obtain 100% efficiency.

Before charging metal hydride batteries, study the main types, which depend on the magnitude of the current.

Drip type charging

It is necessary to use this type of charging for batteries with caution, as it leads to a decrease in the operating period. Since the disconnection of this type of charger is carried out manually, the process needs constant monitoring and regulation. In this case, the minimum current indicator is set (0.1 of the total capacity).

Since with such a charge of ni mh batteries, the maximum voltage is not established, they are guided only by the time indicator. To estimate the time interval, the capacitance parameters that the discharged power source has are used.

The efficiency of a power supply charged in this way is about 65–70 percent. Therefore, manufacturers do not advise using such chargers, since they affect the performance of the battery.

Fast recharge

When determining what current can be used to charge ni mh batteries in fast mode, the recommendations of the manufacturers are taken into account. The magnitude of the current is from 0.75 to 1 of the total capacity. It is not recommended to exceed the set interval, since the emergency valves are activated.

To charge nimh batteries in fast mode, the voltage is set from 0.8 to 8 volts.

The efficiency of fast charging ni mh power supplies reaches 90 percent. But this parameter decreases as soon as the charging time ends. If you do not turn off the charger in a timely manner, then the pressure inside the battery will begin to increase, the temperature indicator will increase.

In order to charge ni mh battery, perform the following actions:

• Pre-charge

This mode is entered when the battery is completely discharged. At this stage, the current is between 0.1 and 0.3 times the capacity. It is forbidden to use high currents. The time interval is about half an hour. As soon as the voltage parameter reaches 0.8 volts, the process stops.

• Switch to fast mode

The current build-up process is carried out within 3-5 minutes. The temperature is monitored throughout the entire time period. If this parameter reaches a critical value, then the charger is turned off.

Fast charging of NiMH batteries sets the current to 1 of the total capacity. In this case, it is very important to quickly disconnect the charger so as not to harm the battery.

A multimeter or voltmeter is used to monitor the voltage. This helps to eliminate false alarms, which have a detrimental effect on the performance of the device.

Some chargers for ni mh batteries work not with a constant, but with a pulse current. The supply of current is carried out at a specified frequency. The supply of a pulsed current contributes to the uniform distribution of the electrolytic composition and active substances.

• Additional and maintenance charging

To replenish the full charge ni mh of the battery at the last stage, the current indicator is reduced to 0.3 of the capacity. Duration is about 25-30 minutes. It is forbidden to increase this time period, since this helps to minimize the battery life.

Accelerated charging

Some nickel cadmium battery chargers are equipped with a boost charge mode. For this, the charging current is limited by setting the parameters at a level of 9-10 of the capacity. Reduce the charge current as soon as the battery is charged to 70 percent.

If the battery is charged in an accelerated mode for more than half an hour, then the structure of the conductive leads is gradually destroyed. Experts recommend using such a charge if you have some experience.

How to properly charge power supplies and eliminate the possibility of overcharging? To do this, follow these rules:

1. Temperature control of ni mh batteries. It is necessary to stop charging nimh batteries as soon as the temperature level rises rapidly.
2. There are time limits for nimh power supplies that allow you to control the process.
3. The ni mh rechargeable batteries must be discharged and charged at a voltage of 0.98. If this parameter is significantly reduced, then the chargers are turned off.

Recovery of nickel metal hydride power supplies

The process of restoring ni mh batteries is to eliminate the consequences of the "memory effect" associated with the loss of capacity. This effect is more likely to occur if the unit is not fully charged frequently. The device fixes the lower limit, after which the capacity decreases.

Before restoring the power source, the following items are prepared:

• Light bulb of required power.
• Charger. Before use, it is important to clarify whether the charger can be used for discharging.
• Voltmeter or multimeter to establish voltage.

A light bulb or a charger, which is equipped with the appropriate mode, is supplied to the battery with their own hands in order to completely discharge it. After that, the charging mode is activated. The number of recovery cycles depends on how long the battery has not been used. The training process is recommended to be repeated 1-2 times during the month. By the way, I restore in this way those sources that have lost 5-10 percent of the total capacity.

A fairly simple method is used to calculate the lost capacity. So, the battery is fully charged, after which it is discharged and the capacity is measured.

This process will be greatly simplified if you use a charger with which you can also control the voltage level. It is also beneficial to use such units because the likelihood of a deep discharge is reduced.

If the state of charge of the nickel metal hydride batteries has not been established, then the lamp must be connected carefully. The voltage level is monitored with a multimeter. This is the only way to prevent the possibility of a complete discharge.

Experienced specialists carry out both the restoration of one element and the whole block. During the charging period, the existing charge is equalized.

Restoring a power source that has been in operation for 2–3 years with a full charge or discharge does not always bring the expected result. This is because the electrolytic composition and the conductive leads are gradually changing. Before using such devices, the electrolytic composition is restored.

Watch a video about recovering such a battery.

NiMH Battery Guidelines

The service life of ni mh batteries largely depends on whether overheating or significant overcharging of the power source is not allowed. Additionally, the masters are advised to consider the following rules:

• Regardless of how long power supplies are stored, they must be charged. The percentage of charge must be at least 50 of the total capacity. Only in this case there will be no problems during storage and maintenance.
• Rechargeable batteries of this type are sensitive to overcharging and excessive heat. These indicators have a detrimental effect on the duration of use, the magnitude of the current output. These power supplies require special chargers.
• Training cycles for NiMH power supplies are optional. With the help of a proven charger, the lost capacity is restored. The number of recovery cycles largely depends on the state of the unit.
• Between recovery cycles, they must take breaks, and also learn how to charge the battery in use. This time period is required in order for the unit to cool down, the temperature level dropped to the required value.
• The recharging procedure or the training cycle is carried out only in an acceptable temperature regime: + 5- + 50 degrees. If this indicator is exceeded, then the likelihood of a rapid failure increases.
• When recharging, make sure that the voltage does not drop below 0.9 volts. After all, some chargers do not charge if this value is minimal. In such cases, it is allowed to connect an external source to restore power.
• Cyclic recovery is carried out on condition that there is some experience. After all, not all chargers can be used to discharge the battery.
• The storage procedure includes a number of simple rules. It is not allowed to store the power supply outdoors or in rooms where the temperature level drops to 0 degrees. This provokes solidification of the electrolyte composition.

If not one, but several power sources are charged at the same time, then the state of charge is maintained at the set level. Therefore, inexperienced consumers carry out battery recovery separately.

Nimh batteries are efficient power supplies that are actively used to complete various devices and assemblies. They stand out for certain advantages and features. Before using them, it is mandatory to take into account the basic rules of use.

Video about Nimh batteries

Rechargeable batteries have become the main power source for modern electronic devices. Ni-MH batteries are considered the most popular, as they are practical, durable and can have increased capacity. But for the safety of technical characteristics during the entire service life, you should find out some features of the operation of drives of this class, as well as the correct charging conditions.

Standard Ni-MH batteries

How to properly charge Ni-MH batteries

When you start charging any autonomous storage device, be it a battery of a simple smartphone or a high-capacity battery of a truck, a number of chemical processes begin in it, due to which the accumulation of electrical energy occurs. The energy received by the storage device does not disappear, part of it is spent on charging, and a certain percentage is spent on heat.

The parameter by which the efficiency of battery charging is determined is called the efficiency of an autonomous storage device. Efficiency allows you to determine how the ratio of useful work and its unnecessary losses spent on heating. And in this parameter, nickel-metal hydride batteries and batteries are much inferior to Ni-Cd storage devices, since too much of the energy spent on charging them is simultaneously spent on heating.

Nickel-metal hydride storage can be rebuilt by yourself

To charge the NiMH battery quickly and correctly, the correct current must be set. This value is determined based on such a parameter as the capacity of an autonomous power source. You can increase the current strength, but this should be done at certain stages of charging.

Three types of charging have been identified specifically for nickel-metal hydride batteries:

• Drip. It leaks to the detriment of the durability of the battery, does not stop even after reaching 100% charge. But with trickle charging, the minimum amount of heat is generated.
• Fast. Following the name, we can say that this type of charging is a little faster, due to this input voltage within 0.8 Volts. At the same time, the level of efficiency increases to 90%, which is considered a very good indicator.
• Charge mode. Required to charge the drive to its full capacity. This mode is carried out using a low current for 30-40 minutes.

This is where the features of the charge end, now you should consider each mode in more detail.

Drip charging features

The main feature of the drop charging of NiZn, as well as Ni-MH batteries, is to reduce its heating during the entire process, which can last until the full capacity of the drive is restored.

Standard charger for Ni-MH batteries

What is remarkable about this type of charging:

• A small current, respectively - the absence of a clear framework for the potential difference. The charge voltage can reach its maximum without any negative impact on the life of the drive.
• The efficiency is within 70%. Of course, this indicator is lower than the others, and the time required to fully restore capacity increases. However, this reduces the heating of the battery.

The above indicators can be classified as positive. Now you should pay attention to the negative qualities of drip charging.

• The drip recovery process does not stop even after the full capacity is restored. Constant exposure to even a small current, when the battery is fully charged, quickly renders it unusable.
• It is necessary to calculate the charging time based on factors such as amperage, voltage, etc. Not very convenient and may take too long for some users.

Today's nickel-metal hydride power supplies do not take on trickle charge as negatively as older models. But charger manufacturers are gradually abandoning the use of such a battery recovery.

Fast charge mode for Ni-MH batteries

The ratings for NiMH batteries are:

• The current strength is within 1 A.
• Voltage from 0.8 V.

The data that should be based on are given. For a fast charging mode, it is best to set the current strength equal to 0.75 A. This is quite enough to restore the drive in a short period of time and at the same time not reduce its operational life. If the current is raised more than 1 A, then the consequence may be an emergency release of pressure, at which the release valve opens.

Charger with accurate amperage readings

In order for the fast charging mode not to harm the battery, it is necessary to monitor the end of the process itself. The efficiency of the quick recovery of the capacity is about 90%, which is considered a very good indicator. But at the end of the charging process, the efficiency drops sharply, and the consequence of such a drop is not only the release of a large amount of heat, but also a sharp increase in pressure. Of course, such indicators negatively affect the longevity of the drive.

The fast charging process consists of several stages, which should be considered in more detail.

Confirmation of the availability of charge indicators

Process sequence:

1. A preliminary current is supplied to the drive poles, which is no more than 0.1 A.
2. The charge voltage is within 1.8 V. A higher value will not start charging the battery quickly.

Medium capacity nickel metal hydride cell

The logic in the chargers is programmed for no battery. This means that if the output voltage is more than 1.8 V, then the charger will perceive this as a lack of power supply. A high potential difference also occurs when the battery is damaged.

Diagnostics of the power supply capacity

Before starting the recovery of the capacity, the charger must determine the charge level of the power source, so a quick recovery process cannot begin if it is completely discharged and the potential difference is less than 0.8 V.

To restore the partial capacity of the nickel-metal hydride storage, an additional mode is provided - a preliminary charge. This is a gentle mode that allows the battery to wake up. It is used not only after full recovery of the capacity, but also during long-term storage of the battery.

It should be remembered that in order to maintain the operational life of nickel-metal hydride power supplies, they cannot be completely discharged. Or, if there is no other way out, then do it as little as possible.

What is pre-charge? Process features

To know how to properly charge a battery, you need to understand the pre-charge process.

The main feature of the preliminary capacity recovery mode is that a certain period of time is allocated for it, no more than 30 minutes. The current strength is set in the range from 0.1 A to 0.3 A. With such parameters, there is no unwanted heating, and the battery can calmly "wake up". If the potential difference exceeds 0.8 V, the pre-charge is automatically turned off and the next stage of capacity recovery begins.

Variety of nickel metal hydride products

If, after 30 minutes, the power supply voltage has not reached 0.8 V, this mode is terminated, since the charger detects the power supply as faulty.

Fast battery charging

This stage is the very one, fast charging of the power source. It proceeds with the obligatory observance of several basic parameters:

• Control over the current strength, which should be within 0.5-1 A.
• Control over time indicators.
• Continuous comparison of potential differences. Disabling the recovery process if this indicator drops by 30 mV.

It is very important to monitor the change in voltage parameters, since at the end of fast charging, the battery begins to quickly heat up. Therefore, the memory includes separate nodes responsible for monitoring the voltage of the power supply. The delta voltage control method is specially used for this. But some memory manufacturers use modern developments that turn off the device in the absence of any changes in the potential difference for a long time.

A more expensive option is to install a temperature controller. For example, when the temperature of the Ni-MH drive rises, the fast recovery mode is automatically disabled. This requires expensive temperature sensors or electronic circuits, respectively, the price of the charger itself rises.

Recharge

This stage is very similar to pre-charging a battery, in which the current is set in the range of 0.1-0.3 A, and the whole process takes no more than 30 minutes. Recharging is necessary, since it is this that allows you to equalize the electronic charges in the power source and increase its operational life. But with a longer recovery, on the contrary, there is an accelerated destruction of the battery.

Features of super fast charging

There is another important concept of Ni-MH battery recovery - ultra-fast charging. Which not only quickly restores the power source, but also extends its operational life. This is due to one interesting feature of Ni-MH batteries.

Metal hydride power supplies can be charged with increased currents, but only after reaching 70% of the capacity. If you skip this moment, then the overestimated parameter of the current strength will only lead to the rapid destruction of the battery. Unfortunately, charger manufacturers consider the installation of such control units on their products too costly, and use simpler fast charging.

Convenient finger-type power supplies

Ultra-fast charging should only be performed on new batteries. Higher currents lead to rapid heating, the next stage of which is the opening of the pressure shut-off valve. After opening the shut-off valve, the nickel accumulator cannot be recovered.

Choosing a charger for Ni-MH batteries

Some charger manufacturers are leaning towards products made specifically for charging Ni-MH batteries. And this is understandable, since these power supplies are the largest in many electronic devices.

It is necessary to consider in more detail the functionality of chargers created specifically to restore the capacity of nickel-metal hydride batteries.

• The obligatory presence of several protective functions, which are formed by a certain combination of certain radioelements.
• The presence of a manual or automatic mode for adjusting the current strength. This is the only way to set the different charging stages. The potential difference is usually taken constant.
• Automatic recharging of the battery, even when 100% capacity is reached. This allows you to constantly maintain the basic parameters of the power source, without compromising the operational life.
• Recognition of current sources operating in a different way. A very important parameter, since some types of batteries, with too much charge current, can explode.

The latter function also belongs to the category of special and requires the installation of a special algorithm. Therefore, many manufacturers prefer to abandon it.

Ni-MH power supplies are popular for their durability, ease of use, and affordable price. Many users have already appreciated the positive qualities of these products.

Nickel metal hydride (Ni-MH) batteries are alkaline. These are chemical current sources in which a hydrogen metal hydride electrode acts as the anode, nickel oxide as the cathode, and potassium hydroxide (KOH) alkali as the electrolyte. Ni-MH batteries are similar in design to Ni-Cd batteries. In terms of the processes taking place in them, they are similar to nickel-hydrogen batteries. In terms of their specific energy content, nickel-metal hydride ones are superior to both of these types. In this article, we will take a closer look at the device and characteristics of Ni-MH batteries, as well as their pros and cons.

Nickel-metal hydride began to be created in the middle of the last century. They were designed to overcome the shortcomings they had. During the ongoing research, scientists have developed new nickel-hydrogen batteries used in space technology. They managed to develop a new way to store hydrogen. In a new type of battery, hydrogen was collected in certain materials, or rather alloys of certain metals. These alloys could store a volume of hydrogen a thousand times their own volume. The composition of the alloys consisted of 2 or more metals. One of them accumulated hydrogen, and the other acted as a catalyst, which ensured the transition of hydrogen atoms into the metal lattice.

Various combinations of metals can be used in Ni-MH batteries. As a result, it is possible to change the properties of the alloy. To create nickel-metal hydride batteries, the production of alloys was launched that operate at room temperature and at low hydrogen pressure. The development of various alloys and the improvement of the technology for the production of Ni-MH batteries are ongoing. Modern samples of batteries of this type provide up to 2 thousand charge-discharge cycles. In this case, the capacity of the negative electrode is reduced by no more than 30 percent. This result is achieved by using nickel alloys with various rare earth metals.

Bill received a patent for the LaNi5 alloy in 1975. This was the first example of a nickel-metal hydride battery, where this alloy was used as an active substance. As for the earlier specimens from other metal hydride alloys, the required capacity was not provided there.

The industrial production of Ni-MH batteries was organized only in the mid-eighties, when an alloy of the composition La-Ni-Co was obtained. It allowed the reversible absorption of hydrogen to be carried out for more than one hundred cycles. In the future, all improvements in the design of Ni-MH batteries were reduced to increasing energy density.

Subsequently, the negative electrode was replaced, which gave an increase in the active mass of the positive electrode by 1.3-2 times. It is from the positive electrode that the capacity of this type of battery depends. Ni-MH batteries have higher specific energy parameters than nickel-cadmium batteries.

In addition to the high energy density of nickel-metal hydride batteries, they are also made of non-toxic materials, which makes them easy to use and dispose of. Thanks to these factors, Ni-MH batteries began to spread successfully. Additionally, you can read about for the car.

Nickel Metal Hydride Battery Applications

Ni-MH batteries are widely used to power various electronics operating in an autonomous mode. Most of them are made in the form of AA or AAA batteries. Although there are other designs, including industrial storage batteries. Their scope of application almost completely coincides with nickel-cadmium and even wider, since they do not contain toxic materials.

Features of charging nickel-metal hydride batteries

The number of charge-discharge cycles and the service life of a Ni-MH battery largely depend on the conditions of use. These two values ​​decrease with increasing discharge rate and depth. Also, the charge rate and control of its end have a direct effect. There are various types of NiMH batteries. Depending on the type and operating conditions, the operating time can be 500-1000 charge-discharge cycles and the service life is 3-5 years. This data is valid at 80 percent depth of discharge.

In order for a Ni-MH battery to work reliably throughout the entire service life, certain recommendations of the battery manufacturers must be followed. The temperature regime should be especially observed. Strong discharge (less than 1 volt) and short circuit should not be allowed. Do not use new NiMH batteries in combination with used ones. Do not solder wires or other elements to batteries.

Overcharging for Ni-MH batteries is much more sensitive than for Ni-Cd. For this type of battery, overcharging can cause thermal runaway. In most cases, charging is performed with a current of 0.1 * C for 15 hours. If this is a trickle charge, then the current value is 0.01-0.03C for 30 hours.

There are also accelerated (4-5 hours) and fast (one hour) charging modes. They may be used for nickel-metal hydride batteries with highly active electrodes. In the case of using such modes, it is necessary to control the process by changing the voltage, temperature and other parameters. Fast charge is used to charge Ni-MH batteries used in cell phones, laptops, power tools. But in these devices, various types of lithium batteries have already become dominant.

• First stage. Charge current 1C or more;
• Second stage. Charge with a current of 0.1C (in time from 30 minutes to one hour);
• Final recharge. Charge with a current of 0.05-0.02C (trickle charge).

As a rule, all the basic information about the method of charging nickel-metal hydride batteries is in the manufacturer's instructions. The recommended charging current is marked on the battery case. We also recommend reading a separate article about.

In the general case, the charge voltage at a charging current of 0.3-1C is in the range of 1.4-1.5 volts. Since oxygen is released at the positive electrode, the electricity transferred during charging exceeds the discharge capacity. The capacity return is defined as the discharge capacity / the amount of electricity transferred during charging. When multiplied by 100, we get the return as a percentage. For cylindrical and disk Ni-MH batteries, this value is different and is equal to 85-90 and 75-80, respectively.

How the charge and discharge of metal hydride batteries is controlled. To prevent overcharging of Ni-MH batteries, manufacturers use charge control methods with the installation of sensors in batteries or chargers. Here are the main ways:

• The charge stops at the absolute temperature. During charging, the battery temperature is constantly monitored and when the maximum permissible value is reached, the fast charge stops;
• The charge stops depending on the rate of temperature change. In this case, the slope of the battery temperature curve is monitored. When a certain threshold value is reached, charging stops;
• The charge stops when the voltage drops. When the process of charging a nickel-metal hydride battery comes to an end, the temperature increases and the voltage decreases, and this method works to lower it;
• The charge stops simply when the maximum charge time is reached;
• The charge stops at the maximum pressure. This control method is used in prismatic Ni-MH batteries. The value of the permissible pressure in such accumulators is in the range of 0.05-0.8 MPa and is determined by the design of the battery;
• The charge stops at the maximum voltage value. This method is used in batteries with high internal resistance.

The maximum temperature control method is not accurate enough. With it, the battery can overcharge if it is cold around, or get insufficient charge if it is hot around.

The temperature change control method shows itself well when the charging process is carried out at a low operating temperature. If used in high ambient temperatures, the battery may heat up unnecessarily before disconnecting. With this control method, at low temperatures, the battery receives a larger input capacity than at high temperatures.

During the initial and final stages of recharging Ni-MH rechargeable batteries, the temperature rises rapidly. This can trigger the sensor. Therefore, manufacturers use special timers to protect the sensor triggering.

The voltage drop method shows itself well at low operating temperatures and has much in common with temperature control.

In order to ensure that the charge stops in case the normal interruption does not work, a charge time control is used.

• by maximum temperature (limit 50-60 degrees);
• voltage reduction (5-15 mV);
• by the maximum charge time (taken in the calculation to obtain a capacity of 120 percent of the nominal);
• by maximum voltage (1.6-1.8 V).

The voltage reduction method can be changed for a temperature difference over a certain time (1-2 degrees per minute). In this case, an initial delay of about 5-10 minutes is set.
After a quick charge of the battery has been carried out, the charger can switch to the mode of recharging it with a current of 0.1C-0.2C for a certain time interval.
It is not recommended to charge Ni-MH batteries with constant voltage. This can cause damage. At the final stage of charging, the current increases. It is proportional to the delta of the battery and power supply voltages. And due to the rise in temperature at the end of charging, the battery voltage decreases. If it is kept constant, then thermal failure can occur.

Pros and cons of Ni-MH batteries

Among the advantages of nickel-metal hydride batteries, it is worth noting an increase in specific energy characteristics, but this is not the only advantage over nickel-cadmium batteries.

An important plus is that it was possible to abandon the use of cadmium. This made production more environmentally friendly. At the same time, the technology of disposal of used batteries has been greatly simplified.

Thanks to these advantages of Ni-MH batteries, the volume of their production has increased dramatically compared to nickel-cadmium batteries.

It is also worth noting that Ni-MH batteries do not have a "memory effect" like Ni-Cd batteries. In them, this phenomenon is caused by the formation of nickelate in the cadmium electrode. But problems concerning overcharging of oxide-nickel electrodes persist.

To reduce the discharge voltage during prolonged recharges, you need to periodically (once a month) discharge the battery to 1 volt. Here everything is the same as with nickel-cadmium batteries.

It is worth noting some of the disadvantages of nickel-metal hydride batteries. In some respects, they are inferior to Ni-Cd. Therefore, they cannot completely replace them. Here are some of the cons and limitations:

• Nickel-metal hydride batteries function quite efficiently in a narrow range of currents. This is due to the limited desorption of hydrogen at a high discharge rate;
• When charged, this type of battery generates more heat than nickel-cadmium batteries. Because of this, the installation of temperature relays or fuses is required. Manufacturers put them on the wall in the central part of the battery;
• The danger of polarity reversal and overheating of cells in Ni-MH batteries increases with the life and the number of charge-discharge cycles. Therefore, manufacturers limit storage batteries to ten cells;
• Ni-MH batteries have a fairly high self-discharge. This is due to the reaction of hydrogen from the electrolyte with a nickel oxide electrode. In modern models, this problem is solved by changing the composition of the negative electrode alloys. Not fully resolved, but the results are acceptable;
• Nickel-metal hydride batteries operate over a narrower temperature range. At minus 10 C, almost all of them become inoperative. The same picture is observed at temperatures above 40 C. But there are some series of batteries for which the temperature range is expanded by alloying additives;
• There is an irreversible loss of capacity of the negative electrode when the battery is discharged to zero. The one that the requirements for the discharge process are more stringent than those of Ni-Cd batteries. Manufacturers recommend a cell discharge of up to 1 volt in low voltage batteries or up to 1.1 volts in batteries of seven to ten cells.

We also advise you to read the article about.
Degradation of nickel-metal hydride batteries is determined by a decrease in the sorption of negative electrodes during operation. During the passage of the charge-discharge cycle, the volume of the crystal lattice of the electrode changes. This causes the formation of cracks, corrosion occurs when interacting with an alkaline electrolyte. In this case, the corrosion products pass with the consumption of hydrogen and oxygen from the electrolyte. As a result, the volume of electrolyte decreases and the internal resistance of the battery increases.

The parameters of Ni-MH batteries largely depend on the alloy composition of the negative electrode. Also, the alloy processing technology has a strong influence, which determines the stability of its composition and structure. Therefore, battery manufacturers are serious about choosing alloy suppliers for their products.

Nickel metal hydride batteries replaced nickel-cadmium and nickel-hydrogen batteries. IN Ni-MH batteries, the positive electrode, as in a nickel-cadmium battery, is made of an oxide-nickel alloy, and the negative electrode is made of an alloy nickel with rare earth metals absorbing hydrogen. The main material that determines the characteristics of a Ni-MH battery is precisely hydrogen absorbing alloy which can absorb 1000 times its own volume of hydrogen.

These alloys are composed of two or more metals, one of which absorbs hydrogen, and the other is a catalyst that promotes the diffusion of hydrogen atoms into the metal lattice. The number of possible combinations of metals used is practically unlimited, which makes it possible to optimize the properties of the alloy. The use of these materials for the manufacture of a negative electrode made it possible to increase the loading of active masses of the positive electrode by 1.3-2 times, which determines the capacity of the battery.

therefore nickel metal hydride rechargeable batteries features high energy density compared to its predecessors. Since their production uses non-toxic materials, then the problem of disposal of used batteries is also easier to solve. Ni-MH batteries, unlike Ni-Cd, no "memory effect".

The operating time (number of discharge-charging cycles) and service life are largely determined by the operating conditions. The operating time decreases with increasing depth and rate of discharge and depends on the rate of charge. Accelerated (in 4 - 5 hours) and fast (in 1 hour) charges are possible for Ni-MH batteries with highly active electrodes. Depending on the type, operating mode and operating conditions, the batteries provide from 500 to 1000 discharge-charging cycles at a discharge depth of 80% and have service life from 3 to 5 years... FROM increased load(decrease in discharge time) and at As the temperature decreases, the capacity of the Ni-MH battery decreases... The effect of lowering the temperature on the capacitance is especially noticeable at high discharge rates.

Operating and storage conditions

During storage occurs self-discharge of Ni-MH battery... For a month at room temperature, the loss of capacity is 20-30%, and with further storage, the losses decrease to 3-7% per month. Self-discharge rate rises with increasing temperaturesensitive to overcharge... During the charging of Ni-MH batteries, heat is generated, therefore, in order to prevent overheating of the battery from Ni-MH batteries during fast charging and / or significant overcharging, thermal fuses or thermal relays are installed in them. Ni-MH batteries have a comparatively narrow operating temperature range: most of them are inoperative at temperatures below -10 degrees and above +40 degrees.

Hybrid Vehicle Applications

Hybrid vehicles use rectangular designs. In them, positive and negative electrodes are placed alternately, and a separator is placed between them. The electrode block is inserted into a metal or plastic housing and covered with a sealing cover. Ni-MH batteries use alkaline electrolyte consisting of KOH with the addition of LiOH. While most experts are confident that the future is with lithium-ion batteries, many hybrid vehicles use nickel-metal hydride batteries. They essentially cheaper, and their production is technologically advanced. Are losing they are in weight quality (the ratio of stored energy to mass) and charging range(from 40 to 60%) - only 20% of the total capacity.

History of creation

The first work on the creation of nickel-cadmium batteries began in the 50s. However, it was not until the mid-1970s that alloys were created that made it possible to absorb hydrogen in fairly large volumes. True, the batteries created on their basis had insufficient capacity compared to nickel-cadmium ones.

However, the research did not stop, as a result of which the La-Ni-Co alloy was created, which allows the electrochemically reversible absorption of hydrogen for more than 100 cycles. Ni-MH batteries entered industrial production in the mid-80s. Since then, their design has been constantly improved through the use of new alloys. Nickel alloys with rare-earth metals can provide up to 2000 charge-discharge cycles of the battery with a decrease in the capacity of the negative electrode by no more than 30%.