Metal hydride element. From operating experience

Federal agency of Education

State educational institution of higher professional education

"TOMSK POLYTECHNIC UNIVERSITY"

Electrotechnical Institute

Direction 551300 – Electrical engineering, electromechanics and electrical technology

Department – Electric drive and electrical equipment

Abstract on the discipline

“Sources of guaranteed and uninterrupted power supply for industrial enterprises”

on the topic of NICKEL-METAL HYDRIDE BATTERIES

Students of group 7M142

Krupina N.V._______________

Kondrashov S.A._____________

«_____»________________

Head Professor, Doctor of Technical Sciences

Garganeev A.G._______________

"_____"___________2009

Tomsk – 2009

Introduction

1. Terminology

3. Nickel-metal hydride batteries

4. Basic Ni-MH processes batteries

5. Design of electrodes of Ni-MH batteries

6. Ni-MH battery design

7. Characteristics of Ni-MH batteries

8. Charging Ni-MH battery

9. Advantages and disadvantages of Ni-MH batteries

10. Standards and designations of NM batteries

11. Storage and operation of Ni-MH batteries

12. Manufacturers and prospects of NM batteries

13. Disposal

Conclusion

List of sources used

Introduction

Almost impossible to imagine modern world without any kind of electronic equipment. Digital technologies have fit into our lives so well, making it more convenient and interesting, that we simply cannot refuse them.

However, we should not forget that for the operation of mobile devices, portable power sources are needed that could meet the ever-increasing needs of modern electronics. We've gained WiFi and Bluetooth, freeing ourselves from data cables, but we still remain tied to electrical networks.

Applied science, however, does not stand still, offering more and more new types of electricity sources. On the other hand, it’s still strange that despite the presence of so many new technologies, the batteries of our phones, smartphones, PDAs and other gadgets are still dying. This happens because people think about proper handling of the battery only when it has completely failed and can be scrapped with peace of mind. It should be understood that replacing a battery can cost a pretty penny. We don’t argue that few people like to strictly follow the operating rules, but, unfortunately, only in this way can the battery life be maximized.

Today, batteries of five different electrochemical schemes are common: nickel-cadmium (Ni-Cd), nickel-metal hydride (Ni-MH), lead-acid (Sealed Lead Acid, SLA), lithium-ion (Li-Ion) and lithium-polymer (Li-Polymer). The determining factor for all of the listed batteries is not only portability (i.e. small volume and weight), but also high reliability, and big time work. The main parameters of a battery are energy density (or specific energy by mass), number of charge/discharge cycles, charging and self-discharge rates. A lead-acid battery usually consists of two plates (electrodes) placed in an electrolyte ( water solution sulfuric acid). U nickel-cadmium element the negative and positive plates are rolled together and placed in a metal cylinder. The positive plate is made of nickel hydroxide and the negative plate is made of cadmium hydroxide. The two plates are insulated by a separator, which is moistened with electrolyte.

A nickel-metal hydride battery is structurally similar to a nickel-cadmium battery, but has a different chemical composition electrolyte and electrodes. In a lithium-ion battery, the electrodes and separator are placed in a lithium salt electrolyte.

Exists great amount myths and legends about the supposedly ideal mode of operation, about methods of “training”, storage, methods and modes of charging and restoring batteries, but let’s try to figure it out.

1.Terminology

A battery (from Latin accumulator - collector, accumulo - collecting, accumulating) is a device for storing energy for the purpose of its subsequent use. An electric battery converts electrical energy into chemical energy and provides the reverse conversion as needed. The battery is charged by passing electric current through it. As a result of the chemical reactions caused, one of the electrodes acquires a positive charge, and the other - a negative one.

A battery, as an electrical device, is characterized by the following basic parameters: electrochemical system, voltage, electrical capacity, internal resistance, self-discharge current and service life.

Battery capacity is the amount of energy that a fully charged battery should have. In practical calculations, capacity is usually expressed in ampere-hours (

). The number of amp hours indicates the period of time that a given battery will operate at 1 amp of current. It is worth adding, however, that in modern mobile devices much lower currents are used, therefore battery capacity often measured in milliamp-hours (or , or mAh). The nominal capacity (as it should be) is always indicated on the battery itself or on its packaging. However, the actual capacity does not always coincide with the nominal capacity. In practice, the actual battery capacity ranges from 80% to 110% of the nominal value.

Specific capacity is the ratio of the battery capacity to its dimensions or weight.

A cycle is one sequence of charging and discharging a battery.

Memory effect is the loss of battery capacity during its operation. It manifests itself in the tendency of the battery to adapt to the duty cycle in which the battery has been operating for a certain period of time. In other words, if you charge a battery several times without completely discharging it first, it seems to “remember” its state and next time simply will not be able to discharge completely, therefore, its capacity decreases. As the number of charge-discharge cycles increases, the memory effect becomes more pronounced.

Under such operating conditions, an increase in crystals on the plate occurs inside the battery (the structure of batteries will be discussed below), which reduce the surface of the electrode. With small crystalline formations of the internal working substance, the surface area of the crystals is maximum, therefore, the amount of energy stored by the battery is also maximum. When crystalline formations become larger during operation, the surface area of the electrode decreases and, as a result, the actual capacity decreases.

Figure 1 shows the effect of the memory effect.

Figure 1 – Memory effect.

Self-discharge is the spontaneous loss of stored energy by a battery over time. This phenomenon is caused by redox processes that occur spontaneously and is inherent in all types of batteries, regardless of their electrochemical system. To quantify self-discharge, the value is used lost battery for a certain time of energy, expressed as a percentage of the value obtained immediately after charging. Self-discharge is maximum in the first 24 hours after charging, so it is estimated both for the first day and for the first month after charging. The amount of battery self-discharge depends largely on the ambient temperature. Thus, when the temperature rises above 100°C, self-discharge can double.

2. Batteries: types and origin

The leading positions in the battery production market are occupied by Japan, Taiwan, China, and South Korea, and they are constantly increasing the scale of their “modest” presence in the world market.

There are dozens of different battery designs on the market today, and each manufacturer is trying to achieve the optimal combination of characteristics - high capacity, small size and weight, performance over a wide range of applications. temperature range and in extreme conditions.

At the same time, studies show that more than 65% of mobile and portable technology users want even more capacious batteries, and they are willing to pay a lot of money for the ability to use their “car” (or phone) for several days without recharging. That is why, in most cases, it is necessary to purchase a more capacious battery than the one included in the kit.

According to the electrochemical system, batteries are divided into several types:

Lead-acid (Sealed Lead Acid, SLA);

Nickel-cadmium (Ni-Cd);

Nickel metal hydride (Ni-MH);

Lithium-ion (Li-Ion);

Lithium polymer (Li-Pol);

Fuel.

In modern portable electronics lead acid batteries are no longer used, so we will start our excursion with nickel batteries, still used in batteries for cameras, laptops, video cameras and other devices.

The ancestor of nickel batteries were nickel-cadmium (Ni-Cd) batteries, invented back in 1899 by the Swedish scientist Waldmar Jungner. The principle of their operation was that nickel acts as a positive electrode (cathode), and cadmium acts as a negative electrode (anode). At first, it was an open battery, in which the oxygen released during charging went straight into the atmosphere, which prevented the creation of a sealed case and, coupled with the high cost necessary materials, the start of mass production has noticeably slowed down.

And they were undertaken as an attempt to overcome shortcomings. However, the metal hydride compounds used at that time were unstable and the required characteristics were not achieved. As a result, the development of NiMH batteries has stalled. New metal hydride compounds, stable enough for battery use, were developed in 1980. Since the late 1980s, NiMH batteries have been continuously improved, mainly in terms of energy density. Their developers noted that NiMH technology has the potential to achieve even higher energy densities.

Options

Theoretical energy content (Wh/kg): 300 Wh/kg.
Specific energy intensity: about - 60-72 Wh/kg.
Specific energy density (Wh/dm³): about - 150 Wh/dm³.
EMF: 1.25.
Working temperature: −60…+55 °C .(-40… +55)
Service life: about 300-500 charge/discharge cycles.

Description

Nickel-metal hydride batteries of the Krona form factor, like rule - initial voltage of 8.4 volts, gradually reduces the voltage to 7.2 volts, and then, when the battery energy is exhausted, the voltage decreases rapidly. This type of battery is designed to replace nickel-cadmium batteries. Nickel-metal hydride batteries have approximately 20% greater capacity with the same dimensions, but a shorter service life - from 200 to 300 charge/discharge cycles. Self-discharge is approximately 1.5-2 times higher than that of nickel-cadmium batteries.

NiMH batteries are practically free of the “memory effect”. This means that you can charge a battery that is not completely discharged if it has not been stored in this condition for more than a few days. If the battery has been partially discharged and then not used for a long time (more than 30 days), it must be discharged before charging.

Environmentally friendly.

The most favorable operating mode: low current charge, 0.1 rated capacity, charge time - 15-16 hours ( typical recommendation manufacturer).

Storage

Batteries should be stored fully charged in the refrigerator, but not below 0 degrees. During storage, it is advisable to check the voltage regularly (once every 1-2 months). It should not fall below 1.37. If the voltage drops, you need to charge the batteries again. The only type of battery that can be stored discharged is Ni-Cd batteries.

Low self-discharge NiMH batteries (LSD NiMH)

The low self-discharge nickel-metal hydride battery (LSD NiMH) was first introduced in November 2005 by Sanyo under the Eneloop brand. Later, many global manufacturers introduced their LSD NiMH batteries.

This type of battery has reduced self-discharge, which means it has more long term storage compared to conventional NiMH. The batteries are sold as "ready to use" or "pre-charged" and are marketed as replacements for alkaline batteries.

Compared with regular batteries NiMH, LSD NiMH are most useful when there may be more than three weeks between charging and using the battery. Conventional NiMH batteries lose up to 10% of their charge capacity during the first 24 hours after charging, then the self-discharge current stabilizes at up to 0.5% of capacity per day. For NiMH LSDs this is typically in the range of 0.04% to 0.1% capacity per day. Manufacturers claim that by improving the electrolyte and electrode, they were able to achieve the following advantages of LSD NiMH compared to classical technology:

Among the disadvantages, it should be noted that the capacity is relatively slightly smaller. Currently (2012) the maximum achieved rated capacity of LSD is 2700 mAh.

However, when testing Sanyo Eneloop XX batteries with a nameplate capacity of 2500mAh (min 2400mAh), it turned out that all of the batteries in a batch of 16 pieces (made in Japan, sold in South Korea) have an even higher capacity - from 2550 mAh to 2680 mAh . Tested with LaCrosse BC-9009 charger.

Partial list of long-life batteries (low self-discharge):

Prolife by Fujicell
Ready2Use Accu from Varta
AccuEvolution by AccuPower
Hybrid, Platinum, and OPP Pre-Charged from Rayovac
eneloop by Sanyo
eniTime by Yuasa
Infinium from Panasonic
ReCyko by Gold Peak
Instant by Vapex
Hybrio from Uniross
Cycle Energy from Sony
MaxE and MaxE Plus from Ansmann
EnergyOn from NexCell
ActiveCharge/StayCharged/Pre-Charged/Accu from Duracell
Pre-Charged by Kodak
nx-ready from ENIX energies
Imedion from
Pleomax E-Lock from Samsung
Centura by Tenergy
Ecomax by CDR King
R2G from Lenmar
LSD ready to use from Turnigy

Other benefits of low self-discharge NiMH batteries (LSD NiMH)

Low self-discharge Nickel Metal Hydride batteries typically have significantly lower internal resistance than conventional NiMH batteries. This has a very positive effect in applications with high current consumption:

More stable voltage
Reduced heat generation especially in fast charge/discharge modes
Higher efficiency
Capable of high pulse current output (Example: camera flash charges faster)
Possibility of long-term operation in devices with low power consumption (Example: remote controls, watches.)

Charge methods

Charging is carried out by electric current at a voltage on the element up to 1.4 - 1.6 V. The voltage on a fully charged element without load is 1.4 V. The voltage under load varies from 1.4 to 0.9 V. The voltage without load is completely a discharged battery is 1.0 - 1.1 V (further discharge may damage the cell). To charge the battery, direct or pulsed current with short-term negative pulses is used (to restore the “memory” effect, the “FLEX Negative Pulse Charging” or “Reflex Charging” method).

Monitoring the end of charge by voltage change

One of the methods for determining the end of a charge is the -ΔV method. The image shows a graph of the voltage across the cell when charging. The charger charges the battery with constant current. After the battery is fully charged, the voltage begins to drop. The effect is observed only when sufficiently high currents charging (0.5C..1C). The charger should detect this drop and turn off charging.

There is also the so-called “inflexion” - a method for determining the end of fast charging. The essence of the method is that it is not the maximum voltage on the battery that is analyzed, but the maximum derivative of the voltage with respect to time. That is, fast charging will stop at the moment when the rate of voltage increase is maximum. This allows the fast charging phase to be completed earlier, when the battery temperature has not yet risen significantly. However, the method requires measuring voltage with greater accuracy and some mathematical calculations (calculating the derivative and digital filtering of the resulting value).

Monitoring the end of charge based on temperature changes

When charging a cell with direct current, most of the electrical energy is converted into chemical energy. When the battery is fully charged, the power supply Electric Energy will be converted into heat. When large enough charging current You can determine the end of the charge by a sharp increase in the temperature of the element by installing a battery temperature sensor. The maximum permissible battery temperature is 60°C.

Areas of use

Replacement of a standard galvanic cell, electric vehicles, defibrillators, rocket and space technology, autonomous power supply systems, radio equipment, lighting equipment.

Selecting battery capacity

When using NiMH batteries, you should not always strive for high capacity. The more capacious the battery, the higher (other things being equal) its self-discharge current. For example, consider batteries with a capacity of 2500 mAh and 1900 mAh. Batteries that are fully charged and not used for, for example, a month will lose part of their electrical capacity due to self-discharge. A more capacious battery will lose charge much faster than a less capacious one. Thus, after, for example, a month, the batteries will have approximately equal charge, and after even more time, the initially more capacious battery will contain less charge.

From a practical point of view, high-capacity batteries (1500-3000 mAh for AA batteries) make sense to use in devices with high consumption energy for a short time and without prior storage. For example:

In radio-controlled models;
In a camera - to increase the number of pictures taken in a relatively short period of time;
In other devices in which the charge will be generated in a relatively short period of time.

Low capacity batteries (300-1000 mAh for AA batteries) are more suitable for the following cases:

When the use of the charge does not begin immediately after charging, but after a significant period of time;
For occasional use in devices ( hand lamps, GPS navigators, toys, walkie-talkies);
For long-term use in a device with moderate power consumption.

Manufacturers

Nickel metal hydride batteries are produced different companies, including:

Camelion
Lenmar
Our strength
NIAI SOURCE
Space

Literature

Khrustalev D. A. Batteries. M: Izumrud, 2003.

Notes

Links

GOST 15596-82 Chemical current sources. Terms and Definitions
GOST R IEC 61436-2004 Sealed nickel-metal hydride batteries
GOST R IEC 62133-2004 Rechargeable batteries and batteries containing alkaline and other non-acid electrolytes. Safety requirements for portable sealed batteries and batteries made from them for portable use


Galvanic cell	Galvanic cell Daniel \| Alkaline element \| \| Dry element \| Concentration element \| Zinc air element \| Weston normal element
Electric batteries	Lead Acid \| Silver-zinc \| Nickel-cadmium \| Nickel metal hydride \| Nickel-zinc battery \| Lithium-ion \| Lithium polymer \| Lithium Iron Sulfide \| Lithium Iron Phosphate \| Lithium titanate \| Vanadium \| Iron-nickel
Fuel cells	Direct methanol \| Solid oxide \| Alkaline
Models

From operating experience

NiMH cells are widely advertised as high-energy, cold-resistant and memoryless. Having bought a Canon PowerShot A 610 digital camera, I naturally equipped it with a capacious memory for 500 high-quality photographs, and to increase the duration of shooting I bought 4 NiMH cells with a capacity of 2500 mAh from Duracell.

Let's compare the characteristics of industrially produced elements:

Options		Lithium ion Li-ion	Nickel-cadmium NiCd	Nickel- metal hydride NiMH	Lead-acid Pb
Duration of service charge/discharge cycles		1-1.5 years	500-1000		3 00-5000
Energy capacity, W*h/kg
Discharge current, mA*battery capacity
Voltage of one element, V
Self-discharge rate		2-5% per month	10% for the first day, 10% for each subsequent month	2 times higher NiCd	40% in year
Range permissible temperatures, degrees Celsius	charging
Range permissible temperatures, degrees Celsius	détente		-20... +65
Permissible voltage range, V		2,5-4,3 (coke), 3,0-4,3 (graphite)			5,25-6,85 (for batteries 6 V), 10,5-13,7 (for batteries 12 V)

Table 1.

From the table we see NiMH elements have a high energy capacity, which makes them preferable when choosing.

To charge them, a DESAY Full-Power Harger smart charger was purchased, which provides charging of NiMH cells with their training. The elements were charged efficiently, but... However, on the sixth charge, it died for a long time. Electronics burned out.

After replacing the charger and several charge-discharge cycles, the batteries began to run out in the second or third ten shots.

It turned out that despite the assurances, NiMH cells also have memory.

And most modern portable devices those using them have built-in protection that turns off the power when a certain minimum voltage is reached. This does not allow you to perform complete discharge battery This is where the memory of elements begins to play its role. Cells that are not fully discharged receive an incomplete charge and their capacity decreases with each recharge.

High-quality chargers allow you to charge without losing capacity. But I couldn’t find something like this on sale for elements with a capacity of 2500mAh. All that remains is to periodically train them.

Training NiMH cells

Everything written below does not apply to battery cells with strong self-discharge . They can only be thrown away; experience shows that they cannot be trained.

NiMH training elements consists of several (1-3) discharge-charge cycles.

Discharge is performed until the voltage on the battery cell drops to 1V. It is advisable to discharge the elements individually. The reason is that the ability to accept charge may vary. And it intensifies when charging without training. Therefore, the voltage protection of your device (player, camera, ...) is triggered prematurely and the undischarged element is subsequently charged. The result of this is an increasing loss of capacity.

Discharge must be performed in a special device (Fig. 3), which allows it to be performed individually for each element. If there is no voltage control, then the discharge was carried out until the brightness of the light bulb noticeably decreased.

And if you time the light bulb burning time, you can determine the battery capacity, it is calculated by the formula:

Capacity = Discharge current x Discharge time = I x t (A * hour)

A battery with a capacity of 2500 mAh is capable of delivering a current of 0.75 A to the load for 3.3 hours, if the time obtained as a result of discharging is less, and accordingly the residual capacity is less. And when the required capacity decreases, you need to continue training the battery.

Now, to discharge battery cells, I use a device made according to the circuit shown in Fig. 3.

It is made from an old charger and looks like this:

Only now there are 4 light bulbs, as in Fig. 3. We need to say something about light bulbs separately. If the light bulb has a discharge current equal to the rated one for of this battery or slightly smaller, it can be used as a load and an indicator, otherwise the light bulb is only an indicator. Then the resistor must be of such a value that the total resistance of El 1-4 and the parallel resistor R 1-4 is about 1.6 Ohms. Replacing a light bulb with an LED is unacceptable.

An example of a light bulb that can be used as a load is a 2.4 V krypton flashlight light bulb.

A special case.

Attention! Manufacturers do not guarantee normal work batteries at charging currents exceeding the current accelerated charging I charge must be less than the battery capacity. So for batteries with a capacity of 2500mAh it should be below 2.5A.

It happens that NiMH cells after discharge have a voltage of less than 1.1 V. In this case, it is necessary to apply the technique described in the above article in the PC WORLD magazine. An element or a series group of elements is connected to a power source through a 21 W car light bulb.

Once again I draw your attention! Such elements must be checked for self-discharge! In most cases, it is the elements with reduced voltage that have increased self-discharge. These items are easier to throw away.

It is preferable to charge individually for each element.

For two elements with a voltage of 1.2 V, the charging voltage should not exceed 5-6V. During forced charging, the light bulb also serves as an indicator. When the brightness of the light bulb decreases, you can check the voltage on the NiMH element. It will be greater than 1.1 V. Typically, this initial, forced charging takes from 1 to 10 minutes.

If the NiMH element does not increase the voltage during forced charging for several minutes and gets hot, this is a reason to remove it from charging and discard it.

I recommend using chargers only with the ability to train (regenerate) the cells when recharging. If there are none, then after 5-6 working cycles in the equipment, without waiting total loss containers, train them and reject elements with strong self-discharge.

And they won't let you down.

One of the forums commented on this article "it's written stupidly, but there's nothing else". So this is not “stupid”, but simple and accessible to anyone who needs help in the kitchen. That is, as simple as possible. Advanced people can install a controller, connect a computer, ......, but that’s another story story.

So that it doesn't seem stupid

There are "smart" chargers for NiMH cells.

This charger works with each battery separately.

He can:

work individually with each battery in different modes,

charge batteries in fast and slow mode,

individual LCD display for each battery compartment,

charge each battery independently,

charge from one to four batteries of different capacities and sizes (AA or AAA),

protect the battery from overheating,

protect each battery from overcharging,

determination of the end of charging by voltage drop,

identify faulty batteries,

pre-discharge the battery to residual voltage,

restore old batteries (charge-discharge training),

check battery capacity,

display on the LCD display: - charge current, voltage, reflect current capacitance.

Most importantly, I EMPHASIZE, of this type The devices allow you to work individually with each battery.

According to user reviews, such a charger allows you to restore the majority of neglected batteries, and serviceable ones can be used for the entire guaranteed service life.

Unfortunately, I have not used such a charger, since it is simply impossible to buy it in the provinces, but you can find a lot of reviews in the forums.

The main thing is not to charge at high currents, despite the stated mode with currents of 0.7 - 1A, this is still a small-sized device and can dissipate power of 2-5 W.

Conclusion

Any restoration of NiMh batteries is strictly individual (with each individual element) work. With constant monitoring and rejection of elements that do not accept charging.

And the best way to restore them is with the help of smart chargers that allow you to individually perform rejection and a charge-discharge cycle with each element. And since there are no such devices that automatically work with batteries of any capacity, they are designed for elements of a strictly defined capacity or must have controlled charging and discharging currents!

Scope of application electric batteries quite wide. Household appliances that are familiar to everyone are equipped with small batteries; the battery is slightly large sizes cars are equipped, and very large and capacitive batteries are installed in busy industrial stations. It would seem that, in addition to the user purpose, different types of batteries may have something in common? However, in fact, these batteries have more than enough similarities. Perhaps one of the main possible similarities between batteries is the principle of organizing their operation. In today’s material, our resource decided to consider exactly one of these. To be more precise, below we will talk about the functioning and operating rules of nickel-metal hydride batteries.

The history of the appearance of nickel-metal hydride batteries

The creation of nickel-metal hydride batteries began to arouse considerable interest among engineering representatives more than 60 years ago, that is, in the 50s of the 20th century. Scientists specializing in the study physical and chemical properties batteries, we seriously thought about how to overcome the shortcomings of the popular ones at that time nickel cadmium batteries. Perhaps one of the main goals of scientists was to create a battery that could speed up and simplify the process of all reactions associated with the electrolytic transfer of hydrogen.

As a result, it was only by the end of the 70s that specialists managed to first design, and then create and fully test more or less high-quality nickel-metal hydride batteries. The main difference between the new type of battery and its predecessors was that it had strictly defined places for the accumulation of the bulk of hydrogen. More precisely, the accumulation of the substance occurred in the alloys of several metals located on the battery electrodes. The composition of the alloys had such a structure that one or more metals accumulated hydrogen (sometimes several thousand times their volume), and other metals acted as catalysts for electrolytic reactions, ensuring the transition of the hydrogen substance into the metal lattice of electrodes.

The resulting battery, which has a hydrogen metal hydride anode and a nickel cathode, received the abbreviation “Ni-MH” (from the name of conductive, storage substances). Such batteries operate on alkaline electrolyte and provide an excellent charge-discharge cycle - up to 2,000 thousand for one full battery. Despite this, the road to designing Ni-MH batteries has not been easy, and currently existing samples are still being upgraded. The main vector of modernization is aimed at increasing the energy density of batteries.

Note that today nickel-metal hydride batteries are mostly produced based on the LaNi5 metal alloy. The first example of such batteries was patented in 1975 and began to be actively used in wide industry. Modern nickel-metal hydride batteries have a high energy density and are made from completely non-toxic raw materials, making them easy to dispose of. Perhaps it is precisely because of these advantages that they have become very popular in many areas where long-term storage of electrical charge is required.

Design and principle of operation of a nickel-metal hydride battery

Nickel-metal hydride batteries of all sizes, capacities and purposes are produced in two main types of shapes - prismatic and cylindrical. Regardless of the form, such batteries consist of the following mandatory elements:

metal hydride and nickel electrodes (cathodes and anodes), forming a galvanic element of a grid structure, which is responsible for the movement and accumulation of electrical charge;
separator areas that separate the electrodes and also participate in the process of electrolytic reactions;
output contacts giving off external environment accumulated charge;
a cover with a valve built into it, necessary to relieve excess pressure from the accumulator cavities (pressure over 2-4 megapascals);
a heat-protective and durable case housing the battery elements described above.

The design of nickel-metal hydride batteries, like many other types of this device, is quite simple and does not present any particular difficulties in consideration. This is clearly shown in the following battery design diagrams:

The operating principles of the batteries under consideration, in contrast to their general design, look slightly more complicated. To understand their essence, let's pay attention to the step-by-step operation of nickel-metal hydride batteries. In a typical version, the operating stages of these batteries are as follows:

The positive electrode, the anode, carries out oxidative reaction with hydrogen absorption;
The negative electrode, the cathode, implements the reduction reaction in hydrogen disabsorption.

In simple terms, an electrode grid organizes the ordered movement of particles (electrodes and ions) through specific chemical reactions. In this case, the electrolyte does not directly participate in the main reaction of electricity generation, but is activated only under certain circumstances of the operation of Ni-MH batteries (for example, during recharging, implementing the oxygen circulation reaction). We will not consider in more detail the principles of operation of nickel-metal hydride batteries, since this requires special chemical knowledge, which many readers of our resource do not have. If you want to learn about the principles of battery operation in greater detail, you should turn to technical literature, which covers in as much detail as possible the course of each reaction at the ends of the electrodes, both when charging and discharging the batteries.

Characteristics of standard Ni-MH battery can be seen in the following table (middle column):

Operating rules

Any battery is a relatively unpretentious device to maintain and operate. Despite this, its cost is often high, so every owner of a particular battery is interested in increasing its service life. Regarding batteries of the “Ni-MH” formation, extend operational period not so difficult. For this it is enough:

Firstly, follow the rules for charging the battery;
Secondly, use it correctly and store it when not in use.

We’ll talk about the first aspect of battery maintenance a little later, but now let’s turn our attention to the main list of rules for operating nickel-metal hydride batteries. A template list of these rules is as follows:

Nickel-metal hydride batteries should only be stored in their charged state at a level of 30-50%;
It is strictly forbidden to overheat Ni-MH batteries, since compared to the same nickel-cadmium batteries, the batteries we are considering are much more sensitive to heat. Work overload negatively affects all processes occurring in the cavities and outputs of the battery. Current output suffers especially;
Never recharge nickel-metal hydride batteries. Always adhere to the charging rules described in this article or reflected in the technical documentation for the battery;
In progress poor exploitation or long-term storage, “train” the battery. Often a periodically carried out charge-discharge cycle (about 3-6 times) is sufficient. It is also advisable to subject new Ni-MH batteries to similar “training”;
Nickel-metal hydride batteries should be stored at room temperature. temperature conditions. The optimal temperature is 15-23 degrees Celsius;
Try not to discharge the battery to the minimum limit - a voltage less than 0.9 Volts for each cathode-anode pair. Nickel-metal hydride batteries, of course, can be restored, but it is advisable not to bring them to a “dead” state (we’ll also talk about how to restore a battery below);
Monitor the design quality of the battery. Serious defects, lack of electrolyte and the like are not allowed. The recommended frequency of checking the battery is 2-4 weeks;
In the case of using large stationary batteries It is also important to follow the rules:
- their current repairs(at least once a year):
- capital restoration (at least once every 3 years);
- reliable fastening of the battery at the place of use;
- availability of lighting;
- using the correct chargers;
- and compliance with safety precautions for using such batteries.

It is important to adhere to the described rules not only because such an approach to the operation of nickel-metal hydride batteries will significantly extend their service life. They also guarantee safe and generally trouble-free use of the battery.

Charging rules

It was previously noted that operating rules are not the only thing that is required to achieve the maximum operating life of nickel-metal hydride batteries. In addition to proper use, it is extremely important to charge such batteries correctly. In general, answering the question “How to properly charge a Ni-MH battery?” is quite difficult. The fact is that each type of alloy used on battery electrodes requires certain rules for this process.

Summarizing and averaging them, we can highlight the following fundamental principles of charging nickel-metal hydride batteries:

Firstly, you must comply right time charging. For most Ni-MH batteries, it is either 15 hours at a charging current of about 0.1 C, or 1-5 hours at a charging current in the range of 0.1-1 C for batteries with highly active electrodes. Exceptions are rechargeable batteries, which can take more than 30 hours to charge;
Secondly, it is important to monitor the temperature of the battery during charging. Many manufacturers do not recommend exceeding a temperature maximum of 50-60 degrees Celsius;
And thirdly, the charging procedure should be taken into account. This approach is considered optimal when the battery is discharged with a rated current to an output voltage of 0.9-1 Volts, after which it is charged to 75-80% of its capacity. maximum capacity. It is important to take into account that when fast charging(supplied current is more than 0.1) it is important to organize precharging with high current supplied to the battery for about 8-10 minutes. After this, the charging process should be organized with a smooth increase in the voltage supplied to the battery to 1.6-1.8 Volts. By the way, during normal recharging of a nickel-metal hydride battery, the voltage often does not change and is normally 0.3-1 Volt.

Note! The rules for charging batteries noted above are of an average nature. Don't forget that for specific brand Nickel-metal hydride batteries may differ slightly.

Battery recovery

Along with the high cost and rapid self-discharge, Ni-MH batteries have another drawback - a pronounced “memory effect”. Its essence lies in the fact that when systematically charging a not completely discharged battery, it seems to remember this and, over time, significantly loses its capacity. To neutralize such risks, owners similar batteries it is necessary to charge maximally discharged batteries, as well as periodically “train” them through the recovery process.

It is necessary to restore nickel-metal hydride batteries during “training” or when they are severely discharged as follows:

First of all, you need to prepare. To restore you will need:
- high-quality and, preferably, smart charger;
- tools for measuring voltage and current;
- any device capable of consuming energy from a battery.
After preparation, you can already wonder how to restore the battery. First, you need to charge the battery according to all the rules, and then discharge it according to the voltage at the battery outputs of 0.8-1 Volts;
Then the restoration itself begins, which, again, must be carried out in accordance with all the rules for charging nickel-metal hydride batteries. Standard Process recovery can be carried out in two ways:
- The first is if the battery shows signs of “life” (usually when discharged at a level of 0.8-1 Volts). Charging takes place with a constant increase in the supplied voltage from 0.3 to 1 Volt with a current of 0.1 C for 30-60 minutes, after which the voltage remains unchanged and the current increases to 0.3-0.5 C;
- The second is if the battery does not show signs of “life” (with a discharge of less than 0.8 Volts). In this case, charging is carried out with a 10-minute pre-charge high current for 10-15 minutes. After this, the steps described above are carried out.

It is worth understanding that the restoration of nickel-metal hydride batteries is a procedure that must be carried out periodically for absolutely all batteries (both “living” and “non-living”). Only this approach to using this type of battery will help you get the most out of them.

Perhaps this is where the story on today’s topic can end. We hope that the material presented above was useful to you and provided answers to your questions.

If you have any questions, leave them in the comments below the article. We or our visitors will be happy to answer them

Ni-MH batteries(nickel metal hydride) are included in the alkaline group. They are current sources of a chemical type, where nickel oxide acts as the cathode, and a hydrogen metal hydride electrode acts as the anode. Alkali is an electrolyte. They are similar to nickel-hydrogen batteries, but are superior in energy capacity.

The production of Ni-MH batteries began in the mid-twentieth century. They were developed taking into account the shortcomings of outdated nickel-cadmium batteries. NiNH can use different combinations of metals. For their production, special alloys and metals were developed that work at room temperature and low hydrogen pressure.

Industrial production began in the eighties. Alloys and metals for Ni-MH are still being manufactured and improved today. Modern devices This type can provide up to 2 thousand charge-discharge cycles. A similar result is achievable due to the use of nickel alloys with rare earth metals.

How are these devices used?

Nickel-metal hydride devices are widely used to power various types of electronics that operate in autonomous mode. They are usually made in the form of AAA or AA batteries. Other versions are also available. For example, industrial batteries. The scope of use of Ni-MH batteries is slightly wider than that of nickel-cadmium batteries, because they do not contain toxic materials.

Currently being sold on domestic market Nickel-metal hydride batteries are divided into 2 groups according to capacity - 1500-3000 mAh and 300-1000 mAh:

First used in devices that have increased energy consumption in a short time. These are all kinds of players, radio-controlled models, cameras, video cameras. In general, devices that quickly consume energy.
Second used when energy consumption begins after a certain time interval. These are toys, flashlights, walkie-talkies. Battery-powered devices operate on batteries that consume electricity moderately and remain offline for a long time.

Charging Ni-MH devices

Charging can be drip and fast. Manufacturers do not recommend the first because it makes it difficult to accurately determine when the current supply to the device has stopped. For this reason, a powerful overcharge may occur, which will lead to battery degradation. using the quick option. The efficiency here is slightly higher than that of the drip type of charging. The current is set to 0.5-1 C.

How to charge a hydride battery:

the presence of a battery is determined;
device qualification;
pre-charge;
fast charging;
recharging;
maintenance charging.

When fast charging you need to have a good charger. It must control the end of the process according to different criteria independent of each other. For example, Ni-Cd devices have enough voltage delta control. And with NiMH, the battery needs to monitor temperature and delta at a minimum.

For proper operation Ni-MH should remember the “Rule of the Three Ps”: “ Do not overheat”, “Do not overcharge”, “Do not overdischarge”.

To prevent battery overcharging, the following control methods are used:

Termination of charge based on temperature change rate . Using this technique, the battery temperature is constantly monitored during charging. When the readings rise faster than necessary, charging stops.
Method of stopping charging based on its maximum time .
Termination of charge by absolute temperature . Here the temperature of the battery is monitored during the charging process. Upon reaching maximum value fast charge stops.
Negative delta voltage termination method . Before the battery completes charging, the oxygen cycle raises the temperature of the NiMH device, causing the voltage to drop.
Maximum voltage . The method is used to turn off the charge of devices with increased internal resistance. The latter appears at the end of the battery life due to lack of electrolyte.
Maximum pressure . The method is used for prismatic batteries large capacity. The level of permitted pressure in such a device depends on its size and design and is in the range of 0.05-0.8 MPa.

To clarify the charging time of a Ni-MH battery, taking into account all the characteristics, you can use the formula: charging time (h) = capacity (mAh) / charger current (mA). For example, there is a battery with a capacity of 2000 milliamp-hours. The charge current in the charger is 500 mA. The capacity is divided by the current and the result is 4. That is, the battery will charge in 4 hours.

Mandatory rules that must be followed for the proper functioning of the nickel-metal hydride device:

These batteries are much more sensitive to heat than nickel-cadmium batteries; they cannot be overloaded . Overload will negatively affect current output (the ability to hold and release accumulated charge).
Metal hydride batteries can be “trained” after purchase . Perform 3-5 charge/discharge cycles, which will allow you to reach the limit of capacity lost during transportation and storage of the device after leaving the conveyor.
Batteries should be stored with a small amount of charge. , approximately 20-40% of the nominal capacity.
After discharging or charging, allow the device to cool down. .
If in electronic device the same battery assembly is used in recharging mode , then from time to time you need to discharge each of them to a voltage of 0.98, and then fully charge them. It is recommended to perform this cycling procedure once every 7-8 battery recharging cycles.
If you need to discharge NiMH, you should stick to the minimum value of 0.98 . If the voltage drops below 0.98, it may stop charging.

Reconditioning of Ni-MH batteries

Due to the “memory effect”, these devices sometimes lose some characteristics and most of their capacity. This occurs during repeated cycles of incomplete discharge and subsequent charging. As a result of this operation, the device “remembers” a lower discharge limit, for this reason its capacity decreases.

To get rid of this problem, you need to constantly perform training and recovery. The light bulb or charger discharges to 0.801 volts, then the battery is fully charged. If for a long time If the battery has not undergone the recovery process, it is advisable to perform 2-3 similar cycles. It is advisable to train it once every 20-30 days.

Manufacturers of Ni-MH batteries claim that the “memory effect” takes up approximately 5% of the capacity. You can restore it with the help of training. An important point at Ni-MH reduction is that the charger has a discharge function with minimum voltage control. What is needed to prevent strong discharge devices during recovery. This is indispensable when the initial state of charge is unknown and it is impossible to guess the approximate discharge time.

If the state of charge of the battery is unknown, it should be discharged under full voltage control, otherwise such restoration will lead to deep discharge. When reconditioning a whole battery, it is recommended to first fully charge it to equalize the charge level.

If the battery has been used for several years, then restoration by charging and discharging may be useless. It is useful for prevention during operation of the device. When using NiMH, along with the appearance of the “memory effect,” changes in the volume and composition of the electrolyte occur. It is worth remembering that it is wiser to restore battery cells individually than to restore the entire battery. The battery life is from one to five years (depending on the specific model).

Advantages and disadvantages

A significant increase in the energy parameters of nickel-metal hydride batteries is not their only advantage over cadmium batteries. Having abandoned the use of cadmium, manufacturers began to use a more environmentally friendly metal. It is much easier to resolve issues with .

Due to these advantages and the fact that the metal used in production is nickel, production Ni-MH devices has increased sharply when compared with nickel-cadmium batteries. They are also convenient because they reduce discharge voltage during long-term recharges, a complete discharge (up to 1 volt) must be carried out once every 20-30 days.

A little about the disadvantages:

Manufacturers limited Ni-MH batteries to ten cells , because with increasing charge-discharge cycles and service life, there is a danger of overheating and polarity reversal.
These batteries operate in a narrower temperature range than nickel-cadmium batteries. . Already at -10 and +40°C they lose their performance.
Ni-MH batteries generate a lot of heat when charging , therefore they need fuses or temperature relays.
Increased self-charging , the presence of which is due to the reaction of the nickel oxide electrode with hydrogen from the electrolyte.

Degradation of Ni-MH batteries is determined by a decrease in the sorption capacity of the negative electrode during cycling. During the discharge-charge cycle, the volume of the crystal lattice changes, which contributes to the formation of rust and cracks during the reaction with the electrolyte. Corrosion occurs when the battery absorbs hydrogen and oxygen. This leads to a decrease in the amount of electrolyte and an increase in internal resistance.

It must be taken into account that the characteristics of batteries depend on the processing technology of the negative electrode alloy, its structure and composition. The metal for alloys also matters. All this forces manufacturers to very carefully choose alloy suppliers, and consumers - the manufacturer.