1899, Waldmar Jungner in the open-type
nickel-cadmium batteries, the first to use a nickel plate, almost at the same time, Thomas Edison invented the electric car for the nickel-iron battery. Unfortunately, because these alkaline batteries at the time of the plate material than other batteries for the village much more expensive materials, practical application has been greatly restricted.
Later, Jungner the
nickel-cadmium batteries after several important improvements, performance improved significantly. One of the most important improvement in 1932, scientists began in the nickel batteries in the use of the active substance. They will be active substances into the porous nickel plate, then nickel metal plate into crust. Nickel-cadmium battery development of another important milestone in the history of the 1947 seal of the successful development of
nickel-cadmium batteries. In such a battery, the chemical reactions do not have to emit gases can be combined in the internal battery. Sealed nickel-cadmium battery successful development of the nickel-cadmium batteries on the application of greatly increased.
Sealed nickel-cadmium battery high efficiency, long life cycle, the energy density, small size, light weight, compact, and does not require maintenance, in industrial and consumer products have been widely used.
With the development of space technology, people have the power requirements of getting higher and higher. The mid-1970s, the United States has succeeded in the development power, light weight, long life, low-cost
nickel-metal hydride batteries, and in 1978 succeeded in such batteries used in satellite navigation, nickel-hydrogen batteries and nickel-cadmium batteries with the volume of Than, the capacity can be doubled, but not the heavy metal cadmium pollution problems. Its work and nickel-cadmium battery voltage identical to working life are generally quite, but it has a good charge and have a discharge performance. In recent years, the nickel-metal hydride batteries worldwide attention, an endless stream of new technologies. Nickel-hydrogen battery has just come out, it is necessary to use high-pressure hydrogen storage containers, but people used to store metal hydride hydrogen, which made a low-voltage nickel-hydrogen batteries and even atmospheric pressure. 1992, the Japanese company Sanyo monthly capacity of 2 million nickel-hydrogen batteries. Currently has more than 20 domestic units to develop and produce
nickel-hydrogen batteries, nickel-hydrogen batteries of domestic properties has reached the international advanced level.
Battery parameters
Battery of the five main parameters: the battery capacity, nominal voltage, internal resistance, the discharge termination voltage and end-of-charge voltage.
Battery capacity is usually used Ah (the) said, 1 Ah is in the 1 A discharge under the current one hour. Battery units within the number of active substances containing the decision to charge the battery unit volume and the content of active substances from the battery to use the material and size of a decision, therefore, usually battery size is, the higher capacity. Battery capacity and a parameter is related to the battery charge current. The battery charge current rate is usually used charging that C, C batteries for the rated capacity. For example, with 2 A current of 1 Ah batteries, charging rate is 2 C; Similarly, with 2 A current of 500 mAh battery charge rate is 4 C.
Battery mint, are among the potential negative difference as the nominal battery voltage. Nominal voltage from the plate electrode potential of the electrolyte concentration and the internal decision. When the ambient temperature, the use of time and changes in working conditions, the output voltage of the battery unit slight changes, in addition, the output
voltage batteries and battery power is left to a certain extent relations. Unit nickel-cadmium battery nominal voltage of about 1.3 V (but generally considered to be 1.25 V), nickel-hydrogen battery unit of nominal voltage of 1.25 V.
The resistance of the battery plate in the decision-flow resistance and the resistance. In charge and discharge process, the resistance is the same plate, but the resistance will ion flow with the electrolyte concentration of charged ions and neutral change.
Battery fully charged, a panel of active substances has reached saturation point, to continue charging, the battery voltage will not rise, then known as the voltage charge termination voltage. Nickel-cadmium battery of end-of-charge voltage of 1.75 ~ 1.8 V, nickel-hydrogen battery charge termination voltage of 1.5 V.
Table 1-1 nickel-cadmium battery discharge rate different from the termination voltage discharge
Discharge termination of the battery voltage is allowed to discharge when the minimum voltage. If voltage is lower than the termination voltage discharge to discharge the battery, battery voltage at both ends will rapidly declining, a depth of discharge, so that a panel formed in the normal charge of the product when it difficult to resume, thus affecting the life of the battery. Discharge termination voltage and the rate on discharge. Nickel-cadmium battery voltage discharge and termination of the relationship between the discharge rate as listed in Table 1-1, nickel-hydrogen battery voltage discharge general provisions for the termination of 1 V.
Nickel-cadmium batteries principle
Nickel-cadmium battery cathode materials for nickel hydroxide Asia-graphite and a mixture of negative material for the sponge-like cadmium powder and cadmium oxide powder, the electrolyte is usually sodium hydroxide or potassium hydroxide solution. When the temperature is high, the use of density of 1.17 ~ 1.19 (15 ℃) of sodium hydroxide solution. When the temperature is low, the use of density of 1.19 ~ 1.21 (15 ℃) of potassium hydroxide solution. -15 ℃ in the following, the use of density of 1.25 ~ 1.27 (15 ℃) of potassium hydroxide solution. To take into account low-temperature performance and ability to maintain the charge, sealed nickel-cadmium batteries used density of 1.40 (15 ℃) of potassium hydroxide solution. In order to increase battery capacity and cycle life, usually in the electrolyte by adding a small amount of lithium hydroxide (about a litre of electrolyte and 15 ~ 20 g).
Nickel-cadmium rechargeable batteries, the cathode active material into a plate of nickel hydroxide] [NiOOH, the negative electrode active material into a plate of metal cadmium, nickel-cadmium battery discharge, the board of cathode active material into nickel hydroxide Asia , The negative electrode active material into a plate of cadmium hydroxide.
1. Discharge in the process of electrochemical reaction
(1) negative reaction
On the negative cadmium after the loss of two electronic into the price of cadmium-Cd2 +, and then immediately with the solution of the two hydroxide ion of OH-generation cadmium hydroxide Cd (OH) 2, deposition to the anode plate.
(2) positive reaction
The board of cathode material is nickel hydroxide (NiOOH) crystal. For the price of nickel ions are three (Ni3 +), two each in the lattice of nickel ions can be obtained from the circuit outside the negative electrode to two electronic transfer, the price of generating two-2 Ni2 +. At the same time, the solution of every two water molecules to two ionizing hydrogen ions into the cathode plate, with lattice on the negative ions of oxygen combine the two, creating two hydroxide ion, and then with the lattice on the original two Hydroxide ions together, and the two second-generation nickel price of the two-nickel hydroxide crystals.
Will be more than the sum of the two, that is a
nickel-cadmium battery discharge when the general reaction:
2. Recharging process in the chemical reaction
Charging, the batteries will be positive and negative with the charger connected to the anode and cathode, and the internal battery discharge when exactly the opposite of the electrochemical reaction, that is, reduction in anode, cathode oxidation reactions.
(1) negative reaction
Negative charge at the board of cadmium hydroxide, the first ionization ion and cadmium into hydrogen and oxygen ions, and ions from the outside of cadmium in electrical circuits to generate cadmium atom attached to the very board, and hydroxide ions into the solution to participate in positive reactions:
(2) positive reaction
The role of outside power, the board of the cathode-nickel hydroxide lattice, the price of nickel ions two of the three lost a generation of electronic price of nickel ions, at the same time, two lattice hydroxide ions in the release of a hydrogen Ion, will remain in the lattice of oxygen anions, with the release of hydrogen ions in the solution of hydrogen and oxygen ions combine to form water molecules. Then, two three price of nickel ions and the two oxygen anions and the remaining two hydroxide ions combine to generate two nickel hydroxide crystals:
Will be more than the sum of the two, that is a nickel-cadmium rechargeable 40Y6799 batteries, the electrochemical reaction:
At the end of
rechargeable batteries, rechargeable batteries, will enable the current decomposition of water in the reaction, positive and negative board will be a large number of oxygen and hydrogen precipitation, the electrochemical reaction is as follows:
From the above we can see that electrode reaction, to exclude Sodium hydroxide or potassium hydroxide is not directly involved in the response, since only conductive role. Reaction from the battery, charging water molecules generated in the process, in the course of discharging water consumption, so filling, in the course of discharge of electrolyte concentration in a small, which can not be detected density of charge and discharge level.
3. Terminal voltage
Adequate power, immediately disconnect the charging circuit, nickel-cadmium battery EMF up to around 1.5 V, but quickly fell to 1.31-1.36 V.
Nickel-cadmium battery terminal voltage with the charge and discharge process and changes can be under-said:
Filling Filling U = E + I charge R,
U-= E-- I-R,
From the style, we can see that charging, the
battery voltage discharge than when the high and the charge current is, the higher-voltage; discharge current is, the lower the voltage.
When the nickel-cadmium battery to discharge current discharge standards, the average working voltage of 1.2 V. A discharge rate of 8 h, the 40Y6797 battery voltage dropped to 1.1 V, the battery-end, that is.
4. Capacity and capacity of the main factors affecting
After the battery fully charged, to a certain discharge conditions, the requirement to release the termination voltage at the battery release of the total rated capacity as the battery capacity, with capacity Q discharge current and discharge time to express the product of that type are as follows:
Q = I t (Ah)
Nickel-cadmium battery capacity and the following factors:
① the number of active substances;
② discharge rate;
③ electrolyte.
Discharge current direct impact on the termination voltage discharge. Termination of the required voltage discharge, discharge current is, the smaller the battery capacity.
The use of different components of the electrolyte, the 40Y6795 battery capacity and life have a certain impact. Typically, in high-temperature environment, in order to improve battery capacity, often add a small amount of electrolytes in lithium hydroxide to form the mixed solution. Experimental proof: a litre of electrolyte added 15 ~ 20 g aquifer lithium hydroxide, at normal temperature, capacity can be increased by 4% to 5%, at 40 ℃, the capacity can be increased by 20%. However, the electrolyte lithium-ion over the content, not only increase the resistance to the electrolyte, but also to remain in the cathode board lithium-ion (Li +) slowly infiltrated the internal lattice of positive changes in the chemical have harmful effects .
Electrolyte temperature on a greater impact on the capacity of the battery. This is because as the electrolyte temperature increases, the active substance of the plate chemical reaction also gradually improving.
Electrolyte in the more harmful impurities, the smaller the
battery capacity. The main harmful impurities are carbonate and sulfate. They can increase the resistance of electrolyte, when the low temperature and crystallization easy to plug the porous plate so that the battery capacity dropped significantly. In addition, the carbonate ion and also negative plates, cadmium carbonate attached to generate negative plates on the surface, thus leading to bad conductive to increase the resistance of the battery, the capacity decline.
5. Internal resistance
Nickel-cadmium batteries and the internal resistance of the electrolyte conductivity, structure and size of the plate, and electrolyte conductivity with the density and temperature. Battery electrolyte mainly by the internal resistance of the resistance decision. Potassium hydroxide and sodium hydroxide solution with the density of the resistance coefficient and variable. 18 ℃, potassium hydroxide solution of sodium hydroxide solution and the least resistance coefficient. Usually nickel-cadmium 40Y6793 batteries can be used under the resistance of computing:
6. Efficiency and life
In normal use conditions, the nickel-cadmium battery capacity η Ah efficiency of 67% -75%, electric energy efficiency η Wh 55% to 65%, cycle life of about 2000 times. Η Ah capacity and efficiency of electric energy efficiency η Wh formula is as follows:
(U-Charge and U should take the average voltage)
7. Memory effect
Nickel-cadmium batteries used in the process, if not all electricity End began to take charge, discharge, next time, we can not produce all the electricity. For example, nickel-cadmium batteries only produce 80 percent of the electricity after the start charging, fully charged, the batteries can only produce 80 percent of electricity consumption, a phenomenon called the memory effect.
End all-electric battery, is the crystallization of a small board. After the discharge of the batteries, nickel hydroxide Asia have not been completely turned into nickel hydroxide, the remaining nickel hydroxide Asia will be combined together to form larger crystals. Crystal larger nickel-cadmium battery is a main reason for the memory effect.
Nickel-metal hydride batteries works
Nickel-metal hydride batteries and the same volume compared with the nickel-cadmium battery, the capacity to be doubled, charge and discharge cycle life expectancy is longer, and no memory effect. Nickel-hydrogen battery cathode active material for the NiOOH (discharge) and Ni (OH) 2 (charging), the negative plates active substances for H2 (discharge) and H2O (charging), with 30 percent of the electrolyte hydroxide Potassium solution, charge and discharge the electrochemical reaction is as follows:
Seen from the equation: charging, negative precipitation hydrogen, stored in containers, from cathode-nickel hydroxide, a nickel hydroxide (NiOOH) and H2O; discharge when the hydrogen is consumed on the anode, cathode changed from nickel hydroxide Nickel hydroxide into Asia.
Excessive charging of the electrochemical reaction:
From the formula that the 02K7052 battery charging excessive, the cathode plate precipitation oxygen, hydrogen precipitation negative plates. As a catalyst for the hydrogen electrode area, and hydrogen can readily spread to hydrogen electrode surface, therefore, hydrogen and oxygen in the battery can be easily combined to generate internal water so that the containers of gas pressure remains unchanged, this further compounded the Rates soon, so that the concentration of oxygen in the internal battery, no more than a few per thousand.
Reaction from the above we can see that the response of nickel-hydrogen batteries and nickel-cadmium batteries similar, only negative charge and discharge process of product different from the reaction of the latter two can be seen, nickel-hydrogen batteries can also cause sealed structure . Nickel-metal hydride batteries used in multi-KOH electrolyte solution and to add a small amount of LiOH. Divide or use POROUS Vinylon non-woven fabrics such as nylon nonwoven. In order to prevent rechargeable batteries during the latter part of the internal pressure too high, battery equipped with anti-explosive device.
Of batteries
Nickel-cadmium batteries characteristic curve as shown in Figure 1. When the constant current charge just to put End of battery power when a pressure drop due to internal resistance battery, battery voltage soon rise (A). Since then, the battery charge start, the battery voltage to a lower rate continued to rise. In this context (AB between), the electrochemical reaction to generate a certain rate of oxygen, the oxygen at the same time also with the same rate combined with hydrogen, therefore, the internal battery temperature and low gas pressure.
Figure 1 nickel-cadmium battery charging curve
Battery charging process, the oxygen above the compound of oxygen, increased pressure within the battery. Battery * within the normal pressure of about 1 lb / 2 inches. The charge, according to charging rate, the battery internal pressure will soon increase to 100 pounds force / 2 inches or higher.
Rechargeable batteries on the various methods, nickel-cadmium batteries, the gas is a key issue. Bubble gathered at the plate surface, will reduce the plate surface chemical reactions involved in the area and increase the resistance of the battery. When a rechargeable battery, the large amounts of gas, if not quickly compound, battery internal pressure will increase significantly, this will damage the 02K7055 battery. In addition, too much pressure, a sealed battery will open pores, so that the electrolyte Yisan. If the electrolyte repeatedly put through the stomata Yisan, the thick of the electrolyte increases, inter-plate transfer more difficult, increase the resistance of the battery, the capacity decline.
After a certain period of time after (C), electrolyte begin to bubble, these bubbles gathered at the plate surface, the effective area to reduce the plate, so the impedance of the battery increase, the battery voltage start up faster. This is close to adequate electric signal.
Adequate power, the battery charge is not converted to the
current battery energy storage, but have a board of oxygen in the ultra-positive potential. Oxygen is due to electrolysis and the electrolyte, is not due to the reduction of cadmium hydroxide caused by cadmium. Potassium hydroxide and water in the composition of the electrolyte, hydrogen and oxygen ions into oxygen, water and free electrons, the reaction-to 4 OH-→ O2 ↑ +2 H2O +4 e -
Although the electrolyte of oxygen can quickly produce negative plates in the surface of the electrolyte in the compound, but the battery temperature still significantly higher. In addition because of the charge current used to generate oxygen, so the pressure within the 02K7053 battery increase.
As the large number of hydrogen and oxygen ions from the rarely than in the cadmium hydroxide more easily in the decomposition of oxygen, the temperature inside the battery sharp rise, so that the battery voltage drops. So the battery voltage curve peak (D).
Electrolyte, and the formation of oxygen is exothermic reaction, a rechargeable battery, (E), continuously produce oxygen, so that the battery temperature and pressure increased. If mandatory emission gases, will lead to reduced electrolyte, the battery capacity decline and damage the battery. If the gas can not be quickly discharged, the battery will be explosive.
Use low-rate constant trickle charge, the battery will have a dendrite. These dendrite to the plate through the gap between the spread. In the proliferation of the more serious cases, these dendritic cells will cause some or all of short-circuit.
The rechargeable nickel-metal hydride batteries and nickel-cadmium batteries of similar, charging them in the course of the voltage and temperature curve in Figure 1-2 and 1-3 as shown in Fig. We can see that the end-of-charge, nickel-cadmium battery voltage drop than the nickel-metal hydride batteries is much greater. When the battery capacity of the rated capacity of 80 percent previously, nickel-cadmium battery temperature rise slowly, when the battery capacity reached 90% after the nickel-cadmium batteries before the temperature rose rapidly. When fully charged 02K7053 battery basic, nickel-cadmium / nickel-hydrogen battery temperature rise rate is basically the same.
Charging process and the charging method
Battery charging process can generally be classified into pre-charge, fast charge, charge up, the trickle charge four stages.
In the long term or not the new batteries, used a fast start charging, it will affect the life of the battery. Therefore, the battery should be used on the current charge, the charge to meet certain conditions, known as the pre-charge at this stage.
Fast charging is to use the current charge, the rapid restoration of battery power. Fast charge rate of 1 C above normal in the rapid charge from the battery capacity and charging rate decision.
In order to avoid the charge, a small number of current rechargeable battery charger. Nickel-cadmium rechargeable batteries normal, acceptable C/10 or lower charge rate, this time to charge more than 10 h. A small current charging, the battery will not have too much gas, battery temperature will not be too high. As long as the battery charger received, the constant current low rate of the battery charger will be able to provide very small trickle charge current. Current use of small battery charging, the battery in the amount of heat generated can be naturally dispersed.
Trickle chargers main problem is charging too slow, for example, the storage capacity of 1 Ah batteries, a rechargeable C/10 rate, the charging time to 10 h above. In addition, the rechargeable 02K6928 battery low rate of repeated charging, but also will produce dendrite. Most trickle chargers, all without any voltage or temperature feedback control and therefore can not guarantee sufficient battery power immediately after the shutdown charger.
Rapid charging at constant current charging and charging the two pulse, constant current charging is a constant current of the current charge, the charge is the first pulse by pulse current of batteries. Then let the battery discharge, so cycle. Battery pulse amplitude great, a very narrow width. Usually discharge pulse amplitude of the pulse for charging three times around. Although the amplitude and pulse discharge capacity of the battery, but the charge current amplitude and the ratio remains unchanged, pulse charging, the charge current wave as shown in Figure 1-4.
Charging process, the nickel-cadmium batteries in the nickel hydroxide reduced to sub-nickel hydroxide, cadmium hydroxide reduced to cadmium. In the course of the bubble, gathered on both sides of the plate, this will reduce the effective area of the plate, the plate so that the internal resistance increases. Since the effective area of plate smaller, filling in all of the time required to increase electricity consumption.
Join the discharge pulse, the bubble left the anode plate with the board and the oxygen compound. This polarization process to reduce the cell's internal pressure, temperature and internal resistance. At the same time, filling most of the 02K7054 battery charge is converted to chemical energy, and will not change as a gas and heat.
Charge and discharge pulse width of the plate choice should be able to guarantee restoration of the original crystal structure, thereby eliminating memory effect. Used to discharge polarization measures, can improve efficiency and allow charging high current fast charge
