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The system introduces the two most common high-energy green batteries

2019-06-14

This article will provide a systematic knowledge of the two most common high-energy green rechargeable battery lithium-ion batteries and nickel-metal hydride batteries currently available on the market, so that you can have a comprehensive understanding of these two types of batteries and the angle of comparison between the purchase batteries. Be a reference for battery usage.

First, the definition

       Lithium-ion battery (Li-ion Batteries) is an alkaline storage battery in which a lithium-containing compound is used as a positive electrode and a carbon material is used as a negative electrode.

       Nickel-Metal Hydride battery The positive active material is mainly made of nickel, and the negative electrode active material is mainly an alkaline storage battery made of a hydrogen storage alloy.

Second, the principle

       Lithium-ion batteries mainly rely on lithium ions to move between the positive and negative electrodes to work. During charge and discharge, Li+ intercalation and deintercalation between the two electrodes: when charging the battery, Li+ is deintercalated from the positive electrode, and the negative electrode is in a lithium-rich state through the electrolyte embedded in the negative electrode;

       1. Positive electrode reaction: Lithium ion is embedded during discharge, and lithium ion is deintercalated during charging.

       When charging: LiFePO4 → Li1-xFePO4 + xLi+ + xe−

       When discharging: Li1-xFePO4 + xLi+ + xe− → LiFePO4

       2. Negative electrode reaction: Lithium ion is deintercalated during discharge, and lithium ion is inserted during charging.

       When charging: xLi+ + xe− + 6C → LixC6

       When discharging: LixC6 → xLi+ + xe− + 6C

When the nickel-metal hydride storage battery is being charged, the hydrogen ions (H+) in the potassium hydroxide (KOH) electrolyte are released, and these compounds absorb it to avoid the formation of hydrogen (H2) to maintain the pressure and volume inside the battery. . When the battery is discharged, these hydrogen ions will return to their original places through the opposite process.

       1, when charging

       Positive electrode reaction: Ni(OH)2 + OH- → NiOOH + H2O + e-

       Negative reaction: M + H2O + e- → MH + OH-

       Total reaction: M + Ni(OH)2 → MH + NiOOH

       2, when discharging

       Positive electrode: NiOOH + H2O + e- → Ni(OH)2 + OH-

       Negative electrode: MH + OH- → M + H2O + e-

       Total reaction: MH + NiOOH → M + Ni(OH)2

Third, the characteristics

       1. Voltage: The voltage of a lithium battery is three times that of a nickel-hydrogen battery.

       Lithium-ion battery voltage = 3.6V

       Nickel-metal hydride battery voltage = 1.2V

       2. According to the mass calculation, lithium ion batteries have higher energy density.

       Lithium-ion battery energy ∕ weight = 150 ~ 200Wh / kg (540 ~ 720kJ / kg)

       Ni-MH battery energy ∕ weight = 60-120 Wh / kg (watt hours / kg)

       3. Lithium-ion batteries have higher energy density by volume.

       Lithium-ion battery energy ∕ volume = 250 ~ 530Wh / L (0.9 ~ 1.9kJ / cm3)

       Ni-MH battery energy ∕ volume = 140-300 Wh / L (watt hours / liter) that is 504-1188kJ / kg (kJ / kg)

       4. Output power: Lithium-ion batteries have greater output power.

       Lithium-ion battery power ∕ weight = 300 ~ 1500W / kg (@ 20 seconds)

       Ni-MH battery power ∕ weight = 250-1000 W/kg

       5, self-discharge rate: lithium-ion battery has a lower self-discharge rate

       Lithium-ion battery self-discharge rate < 5% ~ 10% / month, generally less than 2% per month (recoverable)

       Ni-MH battery self-discharge rate = generally 2-30% per month, depending on temperature, low self-discharge model is 10-30% per year

       6, charging and discharging efficiency: Lithium-ion battery charge and discharge rate is higher.

       Lithium-ion battery charge and discharge efficiency = 100%

       Ni-MH battery charge and discharge efficiency = 66%

       7. Number of cycles: The number of cycles of the two batteries is close, and the cycle life is relatively long.

       Lithium-ion battery charge and discharge cycle times = 500 - 2000 times (lithium iron phosphate battery can reach more than 2000 times)

       Ni-MH battery charge and discharge cycle times = 500 -1800 times

       8. Operating temperature range: The temperature range of the two high-performance batteries is very wide, and the discharge characteristics of the nickel-metal hydride storage battery are better in the low temperature environment.

       Lithium-ion battery operating temperature range -20 ° C ~ 60 ° C

       Ni-MH battery operating temperature range -30 ° C ~ 50 ° C (low temperature nickel-metal hydride battery can be used normally at low temperature -40 ° C)

Fourth, the advantages

       1. High specific energy: The distance that can be exercised by one charge is long, and the specific energy of both is very high. Relatively speaking, lithium-ion battery (currently the battery with the highest energy ratio)> nickel-metal hydride storage battery;

       2. High specific power: It can discharge smoothly during high current operation, and the ability to accelerate climbing is good. The specific power of both is very high, and the lithium ion advantage is obvious;

       3, self-discharge small: both have this advantage, lithium-ion battery slightly better;

       4, light weight, small size: the same type of battery nickel-metal hydride battery weight is lighter, smaller, only in the case of output of the same voltage (lithium-ion battery voltage is 3 times that of nickel-metal hydride battery), so that the number of lithium when a single battery combination The ion battery can be reduced by 1/3, thus making the battery weight and volume of the fabricated lithium ion battery smaller and lighter.

       5, low memory effect: lithium-ion battery has no memory effect and therefore has a greater advantage in this respect;

       6, low temperature discharge performance: nickel-hydrogen storage battery is more powerful at low temperature;

       7, long cycle life: the number of cycles are very much, it is cost-effective;

       8, no environmental pollution: both are green batteries, nickel-metal hydride batteries are called the most environmentally friendly batteries, recycling efficiency lithium-ion batteries are slightly inferior;

       9, high marked capacity: nickel-hydrogen battery marked capacity up to 2900mAh (milliampere-hour / mAh), but still not as high as lithium-ion batteries;

       10, can be quickly discharged: both have this advantage, lithium-ion battery capacity is stronger;

       11, short charging time: both have this advantage.

       In addition, nickel-metal hydride batteries are also safe, reliable and maintenance-free. They are called the safest batteries, and the safety performance of lithium-ion batteries needs to be greatly improved. On the other hand, lithium-ion batteries have no memory effect at all. It is more convenient and simple to use, and the nickel-metal hydride storage battery cannot avoid the periodic discharge management operation due to the residual voltage.

Fifth, use

       Lithium-ion batteries are prone to short-circuit conditions during charging, and it is important to be careful not to overcharge.

       Nickel-metal hydride batteries require regular discharge management.

Sixth, the problem

       The two have a common shortcoming, that is, the production process is strict, resulting in relatively high cost and low price. Relatively speaking, lithium batteries are still more cost-effective.

Seven, application

       Nickel-metal hydride batteries are widely used in notebook computers, camcorders, digital cameras and electric bicycles.

       Lithium-ion batteries are widely used in consumer electronics, military products, and aviation products.

Eight, review

Both lithium-ion batteries and nickel-metal hydride batteries are green batteries, which will not cause secondary pollution due to disposal. This is in line with the environmental protection concept, and they are all recyclable, in line with the concept of sustainable development. In addition, our technology in the battery industry is already in the world. Leading level, and the prospects for export of these green batteries are very good. Although the current price is a bit high, some minor problems need to be further solved and improved, but with the joint efforts of our national researchers and R&D personnel, soon It can meet the requirements of high quality, low cost, high efficiency, energy saving, safety and stability, and green environmental protection. The battery with such high green energy and great development potential deserves our promotion and promotion.