Charge discharge of nickel metal hydride batteries. Ni-Cd, Ni-MH and Li-Ion batteries. What is the difference. Advantages and disadvantages. The principle of operation of nickel-metal hydride batteries and the possibility of their replacement

From operating experience

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

Let's compare the characteristics of the elements produced by the industry:

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 of permissible temperatures, degrees Celsius	charging
Range of permissible temperatures, degrees Celsius	detente		-20... +65
Allowable voltage range, V		2,5-4,3 (coke), 3,0-4,3 (graphite)			5,25-6,85 (for batteries 6 B), 10,5-13,7 (for batteries 12 V)

Table 1.

From the table we can see NiMH cells have a high energy capacity, which makes them the preferred choice.

To charge them, an intelligent Charger DESAY Full-Power Harger provides NiMH cell charging and training. The cells were charged with high quality, but ... However, on the sixth charge, it ordered to live a long time. Electronics burned out.

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

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

And most modern portable devices using them have built-in protection that turns off the power when a certain minimum voltage is reached. This prevents the battery from being fully discharged. This is where the memory of the elements begins to play its role. Incompletely discharged cells receive an incomplete charge and their capacity drops with each recharge.

Quality chargers allow charging without loss of capacity. But something I could not find on the sale of this for cells with a capacity of 2500mAh. It remains to periodically train them.

NiMH Cell Training

Everything written below does not apply to battery cells that have a strong self-discharge. ... They can only be thrown away, experience shows that they do not lend themselves to training.

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

Discharging is carried out until the voltage on the battery cell drops to 1V. It is advisable to discharge the cells individually. The reason is that the ability to take charge can vary. And it gets stronger when you charge without training. Therefore, there is a premature operation of the voltage protection of your device (player, camera, ...) and the subsequent charging of an uncharged cell. The result is an increasing loss of capacity.

Discharging 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 performed until a noticeable decrease in the brightness of the light bulb.

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

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

A battery with a capacity of 2500 mA hour 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 discharge is less, respectively, and the residual capacity is less. And with a decrease in the capacity you need, you need to continue training the battery.

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

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

Only now there are 4 bulbs, as in Fig. 3. It is necessary to say separately about light bulbs. If the lamp has a discharge current equal to the nominal for a given battery or slightly less, it can be used as a load and an indicator, otherwise the lamp 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 bulb that can be used as a load is a 2.4V krypton flashlight bulb.

A special case.

Attention! Manufacturers do not guarantee the normal operation of batteries with charging currents exceeding the rapid charging current I charge should be less than the battery capacity. So for batteries with a capacity of 2500mA * hour, 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 MIR PC magazine. An element or series of elements is connected to a power source through a 21 W automotive light bulb.

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

Charging is preferable individual for each element.

For two cells with a voltage of 1.2 V, the charging voltage should not exceed 5-6 V. With forced charging, the light is also an indicator. When the brightness of the bulb decreases, you can check the voltage on the NiMH cell. It will be greater than 1.1 V. Typically, this initial boost charge takes 1 to 10 minutes.

If the NiMH cell, during forced charging for several minutes, does not increase the voltage, it heats up - this is a reason to remove it from the charge and discard it.

I recommend using chargers only with the ability to train (regenerate) cells when recharging. If there are no such, then after 5-6 working cycles in the equipment, without waiting for a complete loss of capacity, train them and reject elements with a strong self-discharge.

And they won't let you down.

In one of the forums commented on this article "it is written stupidly, but there is nothing else". So this is not" stupid ", but simple and available for execution in the kitchen for everyone who needs help. That is, as simple as possible. Advanced can put a controller, connect a computer, ......, but that's another history.

So that it does not seem stupid

There are smart chargers for NiMH cells.

Such a charger works with each battery separately.

He can:

individually work with each battery in different modes,

charge batteries in fast and slow mode,

individual LCD display for each battery compartment,

independently charge each of the batteries,

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 the residual voltage,

restore old batteries (charge-discharge training),

check the capacity of the batteries,

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

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

According to user reviews, such a charger allows you to restore most of the neglected batteries, and serviceable ones to operate the entire guaranteed service life.

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

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

Conclusion

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

And it's best to rebuild them with smart chargers that allow you to individually reject and cycle charge-discharge with each cell. And since such devices do not automatically work with batteries of any capacity, they are intended for cells of a strictly defined capacity or must have controlled charging and discharging currents!

This article about Nickel Metal Hydride (Ni-MH) batteries has long been a classic on the Russian Internet. I recommend reading ...

Nickel-metal hydride (Ni-MH) batteries are analogous to nickel-cadmium (Ni-Cd) batteries in terms of their design, and nickel-hydrogen batteries in terms of electrochemical processes. The specific energy of the Ni-MH battery is significantly higher than the specific energy of Ni-Cd and hydrogen batteries (Ni-H2)

VIDEO: Nickel Metal Hydride (NiMH) Batteries

Comparative characteristics of batteries

Options	Ni-Cd	Ni-H2	Ni-MH
Rated voltage, V	1.2	1.2	1.2
Specific energy: Wh / kg \| Wh / L	20-40 60-120	40-55 60-80	50-80 100-270
Service life: years \| cycles	1-5 500-1000	2-7 2000-3000	1-5 500-2000
Self-discharge,%	20-30 (for 28 days)	20-30 (for 1 day)	20-40 (for 28 days)
Working temperature, ° С	-50 — +60	-20 — +30	-40 — +60

*** The large scatter of some parameters in the table is caused by the different purpose (design) of the batteries. In addition, the table does not include data on modern batteries with low self-discharge.

History of Ni-MH battery

The development of nickel-metal hydride (Ni-MH) rechargeable batteries began in the 50s and 70s of the last century. As a result, new way storing hydrogen in nickel-hydrogen batteries used in spacecraft. In the new element, hydrogen accumulated in alloys of certain metals. Alloys that absorb 1000 times their own volume of hydrogen were found in the 1960s. 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. To create Ni-MH batteries, it was necessary to create alloys that are efficient at low hydrogen pressure and room temperature. Currently, work on the creation of new alloys and technologies for their processing continues throughout the world. 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%. The first Ni-MH battery, which used LaNi5 as the main active material of a metal hydride electrode, was patented by Bill in 1975. In early experiments with metal hydride alloys, nickel-metal hydride batteries were unstable, and the required battery capacity could not be achieved. Therefore, the industrial use of Ni-MH batteries began only in the mid-80s after the creation of the La-Ni-Co alloy, which allows the electrochemically reversible absorption of hydrogen for more than 100 cycles. Since then, the design of Ni-MH rechargeable batteries has been continuously improved towards increasing their energy density. Replacing the negative electrode made it possible to increase the filling of the active masses of the positive electrode by 1.3-2 times, which determines the capacity of the battery. Therefore Ni-MH accumulators have much higher specific energy characteristics in comparison with Ni-Cd accumulators. The success of the distribution of nickel-metal hydride batteries was ensured by the high energy density and non-toxicity of the materials used in their production.

Basic processes of Ni-MH batteries

In Ni-MH batteries, a nickel oxide electrode is used as the positive electrode, as in a nickel-cadmium battery, and a nickel-rare earth alloy electrode that absorbs hydrogen is used instead of a negative cadmium electrode. On the positive oxide-nickel electrode of the Ni-MH battery, the reaction proceeds:

Ni (OH) 2 + OH- → NiOOH + H 2 O + e - (charge) NiOOH + H 2 O + e - → Ni (OH) 2 + OH - (charge)

At the negative electrode, the metal with absorbed hydrogen is converted into a metal hydride:

M + H 2 O + e - → MH + OH- (charge) MH + OH - → M + H 2 O + e - (discharge)

The general reaction in a Ni-MH battery is written as follows:

Ni (OH) 2 + M → NiOOH + MH (charge) NiOOH + MH → Ni (OH) 2 + M (charge)

The electrolyte does not participate in the main current-forming reaction. After reporting 70-80% of the capacity and when overcharging, oxygen begins to evolve at the nickel-oxide electrode,

2OH- → 1 / 2O 2 + H2O + 2e - (overcharge)

which is restored at the negative electrode:

1 / 2O 2 + H 2 O + 2e - → 2OH - (recharge)

The last two reactions provide a closed oxygen cycle. When oxygen is reduced, an additional increase in the capacity of the metal hydride electrode is provided due to the formation of the OH - group.

Design of electrodes of Ni-MH batteries

Metal hydrogen electrode

The main material that determines the characteristics of a Ni-MH battery is a hydrogen-absorbing alloy, which can absorb 1000 times its own volume of hydrogen. The most widespread are alloys of the LaNi5 type, in which part of the nickel is replaced by manganese, cobalt and aluminum to increase the stability and activity of the alloy. To reduce the cost, some manufacturing companies use mish metal instead of lanthanum (Mm, which is a mixture of rare earth elements, their ratio in the mixture is close to that in natural ores), which, in addition to lanthanum, also includes cerium, praseodymium and neodymium. During charge-discharge cycling, the crystal lattice of hydrogen-absorbing alloys expands and contracts by 15-25% due to the absorption and desorption of hydrogen. Such changes lead to the formation of cracks in the alloy due to the increase in internal stress. Cracking causes an increase in surface area, which corrodes when exposed to alkaline electrolyte. For these reasons, the discharge capacity of the negative electrode gradually decreases. In a battery with a limited amount of electrolyte, this creates electrolyte redistribution problems. Corrosion of the alloy leads to chemical passivity of the surface due to the formation of corrosion-resistant oxides and hydroxides, which increase the overvoltage of the main current-forming reaction of the metal hydride electrode. The formation of corrosion products occurs with the consumption of oxygen and hydrogen from the electrolyte solution, which, in turn, causes a decrease in the amount of electrolyte in the battery and an increase in its internal resistance. To slow down the undesirable processes of dispersion and corrosion of alloys that determine the service life of Ni-MH batteries, two main methods are used (in addition to optimizing the composition and production mode of the alloy). The first method consists in microencapsulation of alloy particles, i.e. in covering their surface with a thin porous layer (5-10%) - by weight of nickel or copper. The second method, which has found the most widespread use at present, consists in processing the surface of alloy particles in alkaline solutions with the formation of protective films permeable to hydrogen.

Nickel oxide electrode

In mass production, nickel oxide electrodes are manufactured in the following design modifications: lamellar, lamellar sintered (cermet) and pressed, including tablet. In recent years, lamellar felt and foam electrodes have begun to be used.

Lamellar electrodes

Lamellar electrodes are a set of interconnected perforated boxes (lamellas) made from a thin (0.1 mm thick) nickel-plated steel strip.

Sintered (cermet) electrodes

electrodes of this type consist of a porous (with a porosity of at least 70%) cermet base, in the pores of which the active mass is located. The base is made of finely dispersed carbonyl nickel powder, which, in a mixture with ammonium carbonate or urea (60-65% nickel, the rest is a filler), is pressed, rolled or sprayed onto a steel or nickel mesh. Then the mesh with the powder is subjected to heat treatment in a reducing atmosphere (usually in a hydrogen atmosphere) at a temperature of 800-960 ° C, while the ammonium carbonate or urea decomposes and volatilizes, and the nickel is sintered. The bases obtained in this way have a thickness of 1-2.3 mm, a porosity of 80-85% and a pore radius of 5-20 microns. The base is alternately impregnated with a concentrated solution of nickel nitrate or nickel sulfate and an alkali solution heated to 60-90 ° C, which induces the precipitation of nickel oxides and hydroxides. Currently, the electrochemical method of impregnation is also used, in which the electrode is subjected to cathodic treatment in a solution of nickel nitrate. Due to the formation of hydrogen, the solution in the pores of the plate is alkalized, which leads to the deposition of oxides and hydroxides of nickel in the pores of the plate. Foil electrodes are considered a variety of sintered electrodes. The electrodes are produced by applying on a thin (0.05 mm) perforated nickel tape on both sides, by the method of pulverization, an alcohol emulsion of nickel carbonyl powder containing binders, sintering and further chemical or electrochemical impregnation with reagents. The thickness of the electrode is 0.4-0.6 mm.

Pressed electrodes

Pressed electrodes are made by pressing the active mass under a pressure of 35-60 MPa onto a mesh or steel perforated tape. The active mass consists of nickel hydroxide, cobalt hydroxide, graphite and a binder.

Metal felt electrodes

Metal felt electrodes have a highly porous base made of nickel or carbon fibers. The porosity of these bases is 95% or more. The felt electrode is made on the basis of nickel-plated polymer or carbon-graphite felt. The thickness of the electrode, depending on its purpose, is in the range of 0.8-10 mm. The active mass is introduced into the felt different methods depending on its density. Instead of felt can be used nickel foam obtained by nickel plating of polyurethane foam with subsequent annealing in a reducing environment. In a highly porous medium, a paste containing nickel hydroxide and a binder are usually applied by spreading. After that, the base with the paste is dried and rolled. Felt and foam electrodes are characterized by high specific capacity and long service life.

Ni-MH battery design

Cylindrical Ni-MH batteries

The positive and negative electrodes, separated by a separator, are rolled up in the form of a roll, which is inserted into the housing and closed with a sealing cap with a gasket (Figure 1). The cover has a safety valve that is triggered at a pressure of 2-4 MPa in the event of a battery failure.

Fig. 1. Nickel metal hydride (Ni-MH) battery design: 1-case, 2-cover, 3-valve cap, 4-valve, 5-positive electrode collector, 6-insulating ring, 7-rejection electrode, 8-separator, 9- positive electrode, 10-insulator.

Ni-MH prismatic batteries

In prismatic Ni-MH batteries, 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. A valve or pressure sensor is usually installed on the cover (Figure 2).

Fig. 2. Ni-MH battery design: 1-case, 2-cover, 3-valve cap, 4-valve, 5-insulating gasket, 6-insulator, 7-negative electrode, 8-separator, 9-positive electrode.

Ni-MH batteries use an alkaline electrolyte consisting of KOH with the addition of LiOH. Non-woven polypropylene and polyamide with a thickness of 0.12-0.25 mm, treated with a wetting agent, are used as a separator in Ni-MH batteries.

Positive electrode

Ni-MH batteries use positive nickel oxide electrodes similar to those used in Ni-Cd batteries. In Ni-MH batteries, sintered electrodes are mainly used, and in recent years - felt and polymer foam electrodes (see above).

Negative electrode

Five designs of a negative metal hydride electrode (see above) have found practical application in Ni-MH batteries: - lamellar, when the powder of a hydrogen-absorbing alloy with a binder or without a binder is pressed into a nickel grid; - nickel foam, when a paste with an alloy and a binder is introduced into the pores of the nickel foam base, and then dried and pressed (rolled); - foil, when a paste with an alloy and a binder is applied to perforated nickel or steel nickel foil, and then dried and pressed; - rolled, when the powder of the active mass, consisting of an alloy and a binder, is applied by rolling (rolling) on a stretching nickel grid or copper mesh; - sintered, when alloy powder is pressed onto a nickel mesh and then sintered in a hydrogen atmosphere. The specific capacities of metal hydride electrodes of different designs are close in value and are mainly determined by the capacity of the alloy used.

Characteristics of Ni-MH batteries. Electrical characteristics

Open circuit voltage

Open circuit voltage value Ur.ts. It is difficult to accurately determine Ni-MH systems due to the dependence of the equilibrium potential of the oxide-nickel electrode on the oxidation state of nickel, as well as the dependence of the equilibrium potential of the metal hydride electrode on the degree of its saturation with hydrogen. 24 hours after charging the battery, the open circuit voltage of the charged Ni-MH battery is in the range of 1.30-1.35V.

Rated discharge voltage

Uр at a normalized discharge current Iр = 0.1-0.2C (C is the nominal battery capacity) at 25 ° C is 1.2-1.25V, the usual final voltage is 1V. Voltage decreases with increasing load (see figure 3)

Fig. 3. Discharge characteristics of a Ni-MH battery at a temperature of 20 ° C and different rated load currents: 1-0.2 C; 2-1C; 3-2C; 4-3C

Battery capacity

With an increase in load (decrease in discharge time) and with a decrease in temperature, the capacity of a Ni-MH battery decreases (Figure 4). The effect of lowering the temperature on the capacitance is especially noticeable at high discharge rates and at temperatures below 0 ° C.

Fig. 4. Dependence of the discharge capacity of the Ni-MH battery on the temperature at different discharge currents: 1-0.2C; 2-1C; 3-3C

Safety and service life of Ni-MH batteries

During storage, the Ni-MH battery self-discharges. After a month at room temperature, the loss of capacity is 20-30%, and with further storage, the loss decreases to 3-7% per month. The self-discharge rate increases with increasing temperature (see Figure 5).

Fig. 5. Dependence of the discharge capacity of the Ni-MH battery on the storage time at different temperatures: 1-0 ° C; 2-20 ° C; 3-40 ° C

Charging the Ni-MH Battery

The operating time (number of discharge-charging cycles) and the service life of a Ni-MH battery are largely determined by the operating conditions. The operating time decreases with increasing depth and rate of discharge. The operating time depends on the charge rate and the method of controlling its end. Depending on the type of Ni-MH batteries, operating mode and operating conditions, the batteries provide from 500 to 1800 discharge-charging cycles at a discharge depth of 80% and have a service life (on average) of 3 to 5 years.

To ensure reliable operation of the Ni-MH battery during the guaranteed period, the recommendations and instructions of the manufacturer must be followed. The greatest attention should be paid to the temperature regime. It is advisable to avoid overdischarges (below 1V) and short circuits. It is recommended to use Ni-MH batteries for their intended purpose, avoid combining used and unused batteries, do not solder wires or other parts directly to the battery. Ni-MH batteries are more sensitive to overcharge than Ni-Cd batteries. Overcharging can lead to thermal runaway. Charging is usually carried out with current Ic = 0.1C for 15 hours. Compensation recharge is performed with current Ic = 0.01-0.03C for 30 hours or more. Accelerated (in 4 - 5 hours) and fast (in 1 hour) charges are possible for Ni-MH batteries with highly active electrodes. With such charges, the process is controlled by changing the temperature ΔТ and voltage ΔU and other parameters. Fast charging is used, for example, for Ni-MH batteries that power laptops, cell phones, and electrical tools, although laptops and cell phones now mainly use lithium-ion and lithium-polymer batteries. A three-stage charging method is also recommended: the first stage of a fast charge (1C and higher), a charge at a rate of 0.1C for 0.5-1 h for the final recharge, and a charge at a rate of 0.05-0.02C as a trickle charge. Information on how to charge Ni-MH batteries is usually contained in the manufacturer's instructions, and the recommended charging current is indicated on the battery case. The charging voltage Uc at Ic = 0.3-1C is in the range of 1.4-1.5V. Due to the release of oxygen at the positive electrode, the amount of electricity delivered during charging (Qc) is greater than the discharge capacity (Cp). In this case, the return on capacity (100 Cp / Qc) is 75-80% and 85-90%, respectively, for disk and cylindrical Ni-MH batteries.

Charge and discharge control

To avoid overcharging Ni-MH batteries, the following charge control methods can be used with appropriate sensors installed in rechargeable batteries or chargers:

method of terminating the charge by absolute temperature Tmax. The battery temperature is constantly monitored during the charging process, and when the maximum value is reached, the fast charge is interrupted;
method of terminating the charge by the rate of temperature change ΔT / Δt. With this method, the slope of the temperature curve of the battery is constantly monitored during the charging process, and when this parameter rises above a certain set value, the charge is interrupted;
method of terminating the charge on the negative voltage delta -ΔU. At the end of the battery charge, during the oxygen cycle, its temperature begins to rise, leading to a decrease in voltage;
method of terminating the charge at the maximum charge time t;
method of terminating the charge at the maximum pressure Pmax. It is usually used in prismatic accumulators of large size and capacity. The level of permissible pressure in a prismatic accumulator depends on its design and lies in the range of 0.05-0.8 MPa;
method of terminating the charge at the maximum voltage Umax. It is used to turn off the charge of batteries with a high internal resistance, which appears at the end of their service life due to a lack of electrolyte or at low temperatures.

With the Tmax method, the battery may be overcharged if the ambient temperature drops, or the battery may not be sufficiently charged if the ambient temperature rises significantly. The ΔT / Δt method can be used very effectively to terminate charging at low ambient temperatures. However, if only this method is used at higher temperatures, the batteries inside the batteries will be heated to undesirably high temperatures before the ΔT / Δt value can be reached for shutdown. For a given ΔT / Δt value, a larger inlet capacitance can be obtained at a lower ambient temperature than at a higher temperature. At the beginning of the battery charge (as well as at the end of the charge), the temperature rises rapidly, which can lead to premature disconnection of the charge when using the ΔT / Δt method. To eliminate this, the developers of chargers use timers of the initial delay of the sensor response with the ΔT / Δt method. The -ΔU method is effective for terminating charging at low ambient temperatures rather than at elevated temperatures. In this sense, the method is similar to the ΔT / Δt method. To ensure that charging stops when unforeseen circumstances prevent a normal charging interruption, it is also recommended to use a timer control that adjusts the duration of the charging operation (method t). Thus, for fast charging of storage batteries with rated currents of 0.5-1C at temperatures of 0-50 ° C, it is advisable to use simultaneously the Tmax methods (with a shutdown temperature of 50-60 ° C, depending on the design of batteries and batteries), -ΔU (5- 15 mV per battery), t (usually to obtain 120% of the nominal capacity) and Umax (1.6-1.8 V per battery). Instead of the -ΔU method, the ΔT / Δt method (1-2 ° C / min) with an initial delay timer (5-10 min) can be used. For charge control, see also the corresponding article After a quick charge of the battery, the chargers provide for switching them to recharge with a rated current of 0.1C - 0.2C for a certain time. For Ni-MH batteries it is not recommended to charge at constant voltage, as "thermal failure" of the batteries can occur. This is due to the fact that at the end of the charge, an increase in current occurs, which is proportional to the difference between the supply voltage and the battery voltage, and the battery voltage at the end of the charge decreases due to the increase in temperature. At low temperatures, the charging rate should be reduced. Otherwise, oxygen will not have time to recombine, which will lead to an increase in pressure in the accumulator. For operation in these conditions, Ni-MH batteries with highly porous electrodes are recommended.

Advantages and disadvantages of Ni-MH batteries

A significant increase in specific energy parameters is not the only advantage of Ni-MH batteries over Ni-Cd batteries. Moving away from cadmium also means moving towards cleaner production. The problem of disposal of out-of-order batteries is also easier to solve. These advantages of Ni-MH batteries have determined the faster growth of their production volumes in all the world's leading battery companies in comparison with Ni-Cd batteries.

Ni-MH batteries do not have the "memory effect" inherent in Ni-Cd batteries due to the formation of nickelate in the negative cadmium electrode. However, the effects associated with recharging of the nickel oxide electrode persist. The decrease in the discharge voltage, observed with frequent and long recharges, just like with Ni-Cd batteries, can be eliminated by periodically carrying out several discharges up to 1V - 0.9V. It is enough to carry out such discharges once a month. However, nickel-metal hydride batteries are inferior to nickel-cadmium, which they are intended to replace, in some operational characteristics:

Ni-MH batteries effectively operate in a narrower range of operating currents, which is associated with limited desorption of hydrogen from the metal hydride electrode at very high discharge rates;
Ni-MH batteries have a narrower temperature Range operation: most of them are inoperative at temperatures below -10 ° C and above +40 ° C, although in some series of batteries, the adjustment of the formulations provided the expansion of the temperature limits;
During the charging of Ni-MH batteries, more heat is generated than when charging Ni-Cd batteries, therefore, in order to prevent overheating of the battery from Ni-MH batteries during fast charging and / or significant overcharging, thermo-fuses or thermo-relays are installed in them, which are located on the wall of one of the batteries in the central part of the battery (this applies to industrial battery assemblies);
Ni-MH batteries have an increased self-discharge, which is determined by the inevitability of the reaction of hydrogen dissolved in the electrolyte with a positive oxide-nickel electrode (but, thanks to the use of special alloys of the negative electrode, it was possible to achieve a decrease in the self-discharge rate to values close to those for Ni-Cd batteries );
the danger of overheating when charging one of the Ni-MH batteries of the battery, as well as polarity reversal of a battery with a lower capacity when the battery is discharged, increases with the mismatch of battery parameters as a result of prolonged cycling, therefore, the creation of batteries from more than 10 batteries is not recommended by all manufacturers;
the loss of capacity of the negative electrode, which occurs in a Ni-MH battery when discharging below 0 V, is irreversible, which puts forward more stringent requirements for the selection of batteries in the battery and monitoring the discharge process than in the case of using Ni-Cd batteries, as a rule, it is recommended to discharge to 1 V / ac in low voltage batteries and up to 1.1 V / ac in a battery of 7-10 batteries.

As noted earlier, the degradation of Ni-MH batteries is primarily determined by a decrease in the sorption capacity of the negative electrode during cycling. In the charge-discharge cycle, the volume of the crystal lattice of the alloy changes, which leads to the formation of cracks and subsequent corrosion when reacting with the electrolyte. The formation of corrosion products occurs with the absorption of oxygen and hydrogen, as a result of which the total amount of electrolyte decreases and the internal resistance of the battery increases. It should be noted that the characteristics of Ni-MH batteries significantly depend on the negative electrode alloy and the alloy processing technology to increase the stability of its composition and structure. This forces battery manufacturers to be careful when choosing alloy suppliers, and battery consumers to choose a manufacturer.

Based on materials from the sites pоwеrinfo.ru, "Chip and Dip"

Nickel metal hydride batteries replaced nickel-cadmium and nickel-hydrogen batteries. V 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 the active masses of the positive electrode by 1.3-2 times, which determines the capacity of the battery.

That's why 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... WITH 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

V hybrid vehicles apply 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%.

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 lid.

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 charging

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 electrolyte 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:

Temperature control of ni mh batteries. It is necessary to stop charging nimh batteries as soon as the temperature level rises rapidly.
There are time limits for nimh power supplies that allow you to control the process.
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 brought 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

Nickel metal hydride (Ni-MH) batteries are alkaline. These are chemical current sources, in which a hydrogen metal hydride electrode acts as an anode, nickel oxide acts as a cathode, and an alkali potassium hydroxide (KOH) is 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 impact. 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 time 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, it is necessary to follow the specific recommendations of the battery manufacturers. Especially should be observed temperature regime... 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 have already become dominant Various types lithium batteries.

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 method for controlling the maximum temperature 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 persisted.

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.

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