This article will give a systematic knowledge explanation of the two most common high-energy green rechargeable batteries currently on the market, lithium-ion batteries and nickel-metal hydride batteries, so that everyone can have a comprehensive understanding of these two batteries and compare them in purchasing batteries. Make a reference with battery usage attention.

1. Definition

Lithium-ion batteries (Li-ion Batteries) are alkaline batteries that use lithium-containing compounds as the positive electrode and carbon materials as the negative electrode.

Nickel-Metal Hydride battery is an alkaline battery in which the positive active material is mainly made of nickel and the negative active material is mainly made of hydrogen storage alloy.

2. Principle

Lithium-ion batteries rely primarily on the movement of lithium ions between the positive and negative electrodes to function. During the charging and discharging process, Li+ intercalates and deintercalates back and forth between the two electrodes: when charging the battery, Li+ is deintercalated from the positive electrode, intercalated into the negative electrode through the electrolyte, and the negative electrode is in a lithium-rich state; the opposite is true during discharge.

        1. Positive electrode reaction: lithium ions are intercalated during discharge, and lithium ions are deintercalated during charging.

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

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

        2. Negative electrode reaction: lithium ions are deintercalated during discharge, and lithium ions are inserted during charging.

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

        During discharge: LixC6 → xLi+ + xe− + 6C

When the nickel-hydrogen battery is charging, the hydrogen ions (H+) in the potassium hydroxide (KOH) electrolyte will be released, and these compounds will absorb it to avoid the formation of hydrogen gas (H2) to maintain the pressure and volume inside the battery . When the battery is discharged, these hydrogen ions will return to the original place through the reverse process.

        1. When charging

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

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

        Overall 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

3. Characteristics

1. Voltage: The voltage of the lithium battery is three times that of the Ni-MH battery.

        Li-ion battery voltage = 3.6V

        NiMH battery voltage = 1.2V

        2. Calculated by mass, lithium-ion batteries have higher energy density.

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

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

        3. Calculated by volume, lithium-ion batteries have higher energy density.

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

        Ni-MH battery energy/volume = 140-300 Wh/L (watt hour/liter) or 504-1188kJ/kg (kilojoule/kg)

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

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

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

        5. Self-discharge rate: lithium-ion batteries have a lower self-discharge rate

        Lithium-ion battery self-discharge rate < 5% ~ 10% / month, generally below 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. Charge and discharge efficiency: the charge and discharge rate of lithium-ion batteries is higher.

        Li-ion battery charge and discharge efficiency = 100%

        Ni-MH battery charge and discharge efficiency = 66%

        7. Number of cycles: The cycle times of the two batteries are similar, and the cycle life is relatively long.

        The number of charge and discharge cycles of lithium-ion batteries = 500-2000 times (lithium iron phosphate batteries can reach more than 2000 times)

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

        8. Working temperature range: The temperature range of the two high-performance batteries is very wide. Compared with the low-temperature environment, the discharge characteristics of Ni-MH batteries are better.

        Lithium-ion battery operating temperature range -20℃～60℃

        The working temperature range of Ni-MH batteries is -30℃～50℃ (low-temperature Ni-MH batteries can be used normally at low temperatures of -40℃)

4. Advantages

1. High specific energy: The distance that can be driven by one charge is long, and the specific energy of both is very high. Relatively speaking, lithium-ion batteries (currently the battery with the highest specific energy)>Ni-MH batteries;

        2. High specific power: It can discharge smoothly when working with high current, and has good acceleration and climbing ability. The specific power of both is very high, and the advantage of lithium ion is obvious;

        3. Small self-discharge: Both have this advantage, and lithium-ion batteries are slightly better;

        4. Light weight and small size: Ni-MH batteries of the same type are lighter in weight and smaller in size, but only under the condition of the same output voltage (the voltage of lithium-ion batteries is 3 times that of Ni-MH batteries), so that the number of lithium-ion batteries in a single battery combination The ion battery can be reduced by 1/3, thus making the weight and volume of the formed lithium-ion battery smaller and lighter.

        5. Low memory effect: lithium-ion batteries have no memory effect, so they have greater advantages in this respect;

        6. Good discharge performance at low temperature: Ni-MH battery is stronger at low temperature;

        7. Long cycle life: Both of them have a lot of cycle times, which is very cost-effective;

        8. No environmental pollution: Both are green and environmentally friendly batteries. Ni-MH batteries are known as the most environmentally friendly batteries, and the efficiency of recycling lithium-ion batteries is slightly inferior;

        9. High marked capacity: the marked capacity of Ni-MH battery can reach 2900mAh (milliampere-hour/mAh), but it is still not as high as lithium-ion battery;

        10. Rapid discharge: Both have this advantage, and the lithium-ion battery has a stronger capacity;

        11. Short charging time: both have this advantage.

        In addition, nickel-metal hydride batteries are also safe, reliable, and maintenance-free, and are known as the safest batteries, while 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, but the Ni-MH storage battery cannot avoid regular discharge management operations due to the residual voltage.

5. Use

Lithium-ion batteries are prone to short circuits during charging, and it is critical to be careful not to overcharge.

Ni-MH batteries need regular discharge management,

6. Problem

The two have a common disadvantage, that is, the production process is strict, resulting in relatively high costs and not cheap prices. Relatively speaking, lithium batteries are still more cost-effective.

7. Application

Ni-MH batteries are widely used in fields such as notebook computers, camcorders, digital cameras and electric bicycles.

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

8. Overview

Both lithium-ion batteries and nickel-metal hydride batteries are green batteries, which will not cause secondary pollution due to discarding, which is in line with the concept of environmental protection. Leading level, and the export prospect of these green batteries is 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 scientific research personnel and enterprise R&D personnel, soon It can meet the requirements of high quality and low price, high efficiency and energy saving, safety and stability, and green environmental protection, and such a green high-energy battery with great development potential is worthy of our vigorous promotion and promotion.