New technology: The performance of enclosed lithium batteries is similar to that of lithium-air batteries?

by:CTECHi     2021-08-04

The new chemical method is expected to overcome the shortcomings of lithium-air batteries.

Under the same weight, lithium-air batteries (lithium-air batteries) can provide more power, so they are widely used in electric vehicles and other mobile electronic devices. However, lithium-air batteries have many shortcomings: high heat generation (a large amount of chemical energy is converted into heat energy and not provided to the device), short life, expensive and complicated manufacturing process (charge and discharge air into the battery requires expensive equipment, and very troublesome).

Recently, Li Ju, professor of nuclear engineering at MIT, post-doctoral fellow Zhu Zhi (ZhiZhu) and five others worked at MIT, Argonne National Laboratory The author of Peking University published an article in the journal Nature Energy, reporting a new technology called 'Nano Lithium CathodeThe above problem.

Li Ju said that one of the weaknesses of lithium-air batteries is that the charging and discharging voltages are different. The discharge voltage is 1.2 volts lower than the charging voltage. Therefore, during each charge The energy lost in the form of heat is as high as 30%. 'If you charge too fast, your lithium battery may really burn up.'

Turn off the gas

When a traditional lithium-air battery is discharged, the oxygen in the air is used to chemically react with the lithium in the battery. During charging, the oxygen in the lithium oxide is released into the atmosphere.

The new nano-lithium cathode battery also uses the effects of oxygen and lithium. The difference is that during discharge, oxygen will no longer be released as a gas, but will be enclosed in a solid. Specifically, oxygen is enclosed in three solid compounds in three redox states-Li2O, Li2O2 and LiO2, which are in turn encased in cobalt dioxide glass.

The advantage of this is that the voltage difference during charging and discharging of the nano lithium cathode battery is reduced by 5 times-from 1.2 volts to 0.24 volts, so only 8% The energy is lost in the form of heat during charging. This means that the car battery can be charged at a faster speed without worrying about overheating and catching fire.

The second disadvantage of lithium-air batteries is that the oxygen released in the form of gas will destroy the ion channels in the battery, thus reducing the life of the lithium battery.

The new technology uses cobalt dioxide glass to wrap lithium and oxygen in a nano-scale space. Scientists call this structure nano-lithium. In this way, the transformation of LiO2, Li2O2, and Li2O will not change the macrostructure of the material. In addition, because the nano-lithium particles themselves are very unstable, the cobalt dioxide glass with nano-channels can just stabilize them. Cobalt dioxide also acts as a catalyst in charge and discharge.

Li Ju said that traditional lithium-air batteries are actually just lithium-oxygen batteries, because water vapor and carbon dioxide in the air will react with lithium, so lithium- The air battery must be equipped with a huge auxiliary system to remove water vapor and carbon dioxide, which is a very difficult step. The new solid lithium battery has no such problem.

Built-in anti-overcharge function

The new solid lithium battery also has its own anti-overcharge function, because the battery The chemical reaction will self-regulate through negative feedback. When the battery is fully charged, the reaction will stop automatically. If the traditional battery is overcharged, it will irreversibly damage the battery and even explode. However, the solid lithium battery was continuously charged for 15 days in the experiment, and the charge capacity was 100 times the battery capacity, but the battery was undamaged.

In the charge and discharge experiment, the solid lithium battery is charged and discharged 120 times, and the capacity is only lost 2%, which means that the life of the traditional lithium-air battery is far exceeded. Since the solid lithium battery does not require an auxiliary air purification system, it can be easily applied to electric vehicles and even grid-level energy storage stations.

Because the solid oxygen cathode is much lighter than the cathode of a lithium ion battery, the new solid lithium battery can store twice as much electricity as a lithium ion battery of the same weight. With the improvement of technology, the capacity of new batteries can be doubled.

The greater advantage of the new battery is that it does not require the use of expensive and rare materials. The carbonate electrolyte of this battery is very cheap. In addition, cobalt dioxide glass is 50% lighter than nano lithium particles. Therefore, compared with lithium-air batteries, new batteries are very cheap, safe, and have the potential for large-scale applications. The research team plans to complete the manufacturing of a practical prototype within one year.

Associate Professor Ji Xulei (XiuleiJi) of Oregon State University, who did not participate in the project, said that the performance of the new lithium battery technology has a significant improvement over the traditional lithium-air battery. Superoxide solutes work well in carbonate dielectrics without the intervention of oxygen. In the process of charging and discharging, the cathode material is solid, so the installation and use of the new battery is very convenient.

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