Energy storage batteries are an important part of solar street lamps. Now more and more solar street lamps use lithium-ion batteries. Lithium-ion batteries are currently a widely used battery. They have high energy density, low self-discharge rate, Long cycle life and other advantages. Lithium-ion batteries have been used in many fields, such as wearable devices, electric vehicles, satellites, spacecraft, underwater robots, etc. In the final analysis, the life of lithium batteries mainly includes that after the battery has been used for a while, the capacity decays to 70% of the nominal capacity (battery capacity at room temperature of 25°C, standard atmospheric pressure, and discharged at 0.2C), which can be regarded as the end of life. In the industry, the cycle life is generally calculated by the number of cycles of lithium batteries being fully charged and discharged. During use, irreversible electrochemical reactions will occur inside the lithium battery to reduce the capacity, such as the decomposition of the electrolyte, the degradation of the active material, and the collapse of the positive and negative electrode structures, resulting in a reduction in the number of intercalation and deintercalation of lithium ions. Experiments indicate that a higher discharge rate will cause faster capacity decay. If the discharge current is lower, the battery voltage will be close to the equilibrium voltage and more energy will be released.
However, conventional lithium batteries cannot be charged and discharged at minus 20 degrees Celsius, resulting in the loss of function of the entire solar street light. On the other hand, the low temperature environment greatly reduces the charging and discharging effect of lithium batteries. This characteristic of lithium batteries makes solar street lights unable to function well in cold winter.
So how can we make solar street lights overcome this defect? The answer is – use low temperature Ni-MH batteries
1. What is Ni-MH battery?
Nickel-metal hydride battery is a kind of nickel-based battery, and nickel-based battery refers to an alkaline battery that uses nickelous hydroxide as the positive electrode active material. The so-called alkaline storage battery refers to the storage battery with potassium hydroxide (KOH) and sodium hydroxide (NaOH) aqueous solution as electrolyte. Alkaline batteries include nickel-iron, nickel-cadmium, nickel-metal hydride, and zinc-silver. The advantages of alkaline batteries include high energy density, small self-discharge, good storage performance, can be made into sealed batteries, and are easy to realize miniaturization. Nickel-based batteries currently used in electric vehicles mainly include nickel-cadmium (Ni-Cd) batteries, nickel-zinc (Ni-Zn) batteries and nickel-metal hydride (Ni-MH) batteries. Compared with lead-acid batteries, nickel-cadmium batteries have a specific energy of 55Wh/kg, a specific power of 200W/kg, a cycle life of 2000 times, and fast charging.
Normally, the ambient temperature of the rechargeable battery is around 40°C, but in some real application fields, the ambient temperature of the rechargeable battery is extremely hot, and the ambient temperature of the rechargeable battery can reach 75°C or above. Use high temperature resistant batteries. With high temperature resistant batteries, of course! Low temperature resistant batteries are indispensable. At this stage, the key to high and low temperature resistant batteries are polymer ternary lithium batteries, polymer lithium batteries and nickel metal hydride batteries.
Nickel metal hydride battery This is a battery with excellent performance. Ni-MH batteries are divided into high-voltage Ni-MH batteries and low-voltage Ni-MH batteries. In view of the fact that fossil fuels are less and less used in the large-scale comprehensive utilization of human beings, the comprehensive utilization of hydrogen energy has been paid more and more attention in recent years. As an important direction of hydrogen energy application, nickel-metal hydride battery has received more and more people’s special attention.
2. The life of the NiMH battery.
If the Ni-MH battery is not used, it will be discharged at a rate of 0.2%-0.3% every day, and after a period of storage, even if it is not reused, a small part of its capacity will be effectively lost for a long time, and its life will also be lost. For Ni-MH batteries that meet the conditions, after being fully charged, put them in an environment of 20±5°C for 28 days, and the power will still retain more than 75%; if placed in an environment of 60°C for seven days, the power should also retain more than 75% . The higher the temperature, the faster the NiMH battery will lose its charge.
It is very difficult to say how many years the life span is, mainly because the service life of the rechargeable battery is mainly determined by the number of charge-discharge cycles; how many times you charge and discharge cycles, the time is shorter and the speed is faster, and the time is longer in turn; usually The number of cycles of Ni-MH batteries is between 800 and 1,000 times; batteries with low cycle times have high internal resistance and poor performance indicators, so gradually increasing and cheap batteries usually have low cycle times. Therefore, to measure whether a battery is good or not, one cannot simply seek how high the capacity is, but to consider the battery capacity and the number of cycles comprehensively!
3. Which one has a longer life, Ni-MH battery or lithium battery?
In the usual application environment, the life of Ni-MH batteries will be longer, mainly because Ni-MH batteries have a certain memory effect, so major automobile manufacturers will give them “shallow charge and shallow discharge” when using Ni-MH batteries. In the battery management mode, most of the models equipped with nickel-metal hydride batteries are gasoline-electric hybrid vehicles, and the maximum power consumption of the battery will not exceed 40%.
In other words, when the remaining 60% of the battery power, it will stop discharging and start charging, and the Ni-MH battery will not be fully charged to full. With the support of such a battery management mode, overcharging can be avoided to the greatest extent. Over-discharge, thereby prolonging its life, theoretically speaking, the charge-discharge cycle of the Ni-MH battery can reach tens of thousands of times.
But if Ni-MH batteries use the same discharge depth as lithium-ion batteries in actual use, the service life is not as long as lithium-ion batteries.
4. Advantages of high and low temperature Ni-MH batteries
The high-temperature battery series of nickel-metal hydride batteries can work normally at 70 degrees Celsius, and the normal use environment temperature is 20 degrees Celsius to plus 85 degrees Celsius. The index value is far beyond the level of the same industry. It can carry out various series and parallel combinations according to customer requirements. It is reliable and provides full technical support and services. According to the international standard IEC61951-2 (2003) for nickel-hydrogen batteries, it can ensure the use of 500 One or more charge and discharge cycles, thereby reducing the cost of use for end customers to an extremely low level.
5. Disadvantages of Ni-MH batteries:
The charging efficiency of Ni-MH batteries is the lowest among several types of rechargeable batteries, only 70% (that is to say, the charger generates 0.3 watt-hours of heat for every 1 watt-hour of output during charging, and only 70% of the energy is saved by the battery. ), while the lead-acid battery is 80%, and the lithium-ion battery can reach 95%.
Low-temperature Ni-MH batteries are generally used in various fields such as aeronautical engineering, cruise missile loading equipment, very cold poles, emergency rescue equipment, medical equipment, and industrial production intelligent robots. Once autumn arrives, most places in our country will gradually experience a low temperature climate. A lot of industrial production equipment and instruments with batteries will be affected by a certain low temperature environment, so it is especially important for enterprise manufacturers when you have a low temperature resistant Ni-MH battery. Then let’s take a look at the service life of low-temperature Ni-MH batteries.
6. The service life of low temperature Ni-MH battery
According to the discharge properties of Ni-MH batteries, Ni-MH batteries will be automatically discharged every day if they are not used. Even if they are not used for a long time, their battery life will also be lost. After fully charging the battery, put it in an environment of 20±5°C for 28 days, and more than 75% of the power will remain; if it is placed in an environment of 60°C for seven days, it should also retain more than 75% of the power. The higher the temperature, the faster the NiMH battery will lose its charge.
On the other hand, it is very difficult to say how many years of life, because the service life of rechargeable batteries is mainly determined by the number of charge-discharge cycles; the number of charge-discharge cycles you have, the shorter the time, the faster the speed, and vice versa Long time; Generally speaking, the number of cycles of Ni-MH batteries is 800 to 1,000 times; batteries with low cycle times have high internal resistance and poor performance, so more and more cheap batteries generally have low cycle times. Therefore, to measure whether a battery is good or not, we cannot simply seek how high the capacity is, but consider the battery capacity and the number of cycles comprehensively.
To sum up, in terms of high and low temperature resistance of solar street lights, the use of nickel metal hydride batteries is the best choice. Other batteries have various advantages, but only high and low temperature resistance, Ni-MH batteries are better than other batteries.
