China's water-based batteries have made a major breakthrough? The energy density is twice that of lithium-ion batteries, or even more than some solid-state batteries? Do you know what this means? Water-based batteries are essentially safe and non-explosive batteries, and if the energy density exceeds lithium-ion batteries, it means that a new track may appear in the battery field, no wonder foreign media commented that this breakthrough may bring revolutionary changes to the electric vehicle industry.
The research came from a team led by Professor Li Xianfeng and Professor Fu Qiang of the Dalian Institute of Chemical Physics of the Chinese Academy of Sciences, who developed a high-energy aqueous battery based on halogen multi-electron transfer, with an energy density of up to 1200Wh/L, which is currently the highest energy density of aqueous batteries, and is an order of magnitude improvement, while most of the current commercial lithium-ion batteries are 400-700Wh/L.
For example, the solid-state battery that has been mass-produced by Taiwan Huineng has a volume energy density of 1025Wh/L and a mass energy density of 383Wh/kg, while the semi-solid-state battery of Zhiji Automobile that was announced to be installed some time ago is 368Wh/kg, and that of NIO is 360Wh/kg. The fact that the aqueous battery has surpassed these big hits all of a sudden can be said to be completely unexpected, do you know why I say that?
There are two major disadvantages of aqueous batteries
Because the most criticized thing about the aqueous battery is that its energy density is very low, which can be said to be much lower than that of the lithium-ion battery, and it is low in nature, low in the bones, what is the reason for this? The ions in the aqueous battery are conducted in the form of electrolyte solution, but the solubility of water as a solvent is very limited, and the ion concentration is difficult to increase, which means that the number of active ions that can participate in the battery reaction is limited, which limits the effective charge transfer in the battery and reduces the energy density. For example, traditional aqueous batteries, such as all-vanadium flow batteries and zinc-bromine flow batteries, have energy densities of only about 30Wh/L and 60Wh/L, which are only suitable for large-scale stationary energy storage.
Another criticism of aqueous batteries is that their voltage is relatively low. This is because it is subject to the water splitting voltage, which is usually only about 1.23V. Beyond this value, water will be electrolyzed into hydrogen and oxygen, causing the battery to not work properly, so the total energy that aqueous batteries can provide is limited, and they are not suitable for use as power batteries for electric vehicles.
Solve two major problems in one fell swoop
The Dalian team's research used a halogen solution mixed with iodine and bromide ions as the electrolyte, and optimized the reaction path through the intermediate state of bromide formed during the charge-discharge process, which was like building a wide bridge, successfully realizing the multi-electron transfer reaction, and greatly improving the activity and reversibility of the electrochemical reaction.
The experimental results show that in a certain concentration of iodine ion electrolyte, the aqueous battery can achieve more than 30 moles of electron transfer, so that the specific capacity of the positive side of the battery exceeds 840Ah/L. When this positive electrode and metal cadmium anode are combined to form a whole battery, the energy density is more than 1200Wh/L, which can already be used in power batteries.
Using in-situ light microscopy and Raman spectroscopy, the research team also found that bromide ions can generate polar iodine bromide during battery charging, which is conducive to reacting with water to form iodate, thereby increasing the reaction rate and reducing the charging voltage.
In the process of discharge, iodate is reacted with bromine ions to form bromine and participate in the electrochemical reaction, which realizes the reversible and rapid discharge of iodate, which not only increases the discharge voltage of the battery, but also improves the reduction rate of iodate. This means that the voltage problem of aqueous batteries is also expected to be solved, so that it may be applied to the field of power batteries.
But there are so many studies in the field of batteries, and various breakthroughs are emerging one after another, just like playing at home, why is this research likely to have major breakthrough significance?
Significant
Batteries can actually be divided into three categories, physical batteries, biological batteries, and chemical batteries. Photovoltaics, thermoelectrics, and piezoelectric belong to physical batteries, while microbial fuel cells and enzyme fuel cells belong to biological batteries.
The battery we usually talk about usually refers to chemical batteries, which can be divided into primary batteries and secondary batteries, that is, non-rechargeable and rechargeable, and rechargeable batteries are generally divided into three types, aqueous batteries, organic ion batteries and fuel cells, organic ion batteries include the current lithium-ion and sodium-ion batteries, and fuel cells have hydrogen fuel cells, methanol fuel cells, etc.
The so-called aqueous batteries refer to batteries that use water as the electrolyte solvent, such as nickel-metal hydride batteries, which have also been brilliant for a while, lead-acid batteries, which are widely used in automobiles, but may soon be about to lose their glory, and zinc-based batteries, including zinc-nickel and zinc-air batteries.
NiMH batteries and lead-acid batteries are the most typical aqueous batteries, and they used to be brilliant. But with the rise of electric vehicles, lithium-ion batteries have become superstars in the battery field by virtue of their high energy density, and the voltage of nickel-metal hydride batteries and lead-acid batteries is only 2V.
However, the lithium-ion battery spring breeze is proud, but it also exposes two fatal problems, high cost, flammable, expensive and irritable, so that people who have seen different things have begun to miss the low-cost, non-flammable, non-toxic, and essentially safe water battery. Older people may have used zinc-carbon batteries, that is, dry batteries, often smashed open when they were young, and took out the carbon rods inside for graffiti, have you ever heard that it exploded?
The research of the Dalian team has made a breakthrough in energy density and voltage, can it make the aqueous battery raise its eyebrows, recover the old mountains and rivers, drive away the hot-tempered lithium-ion battery, and regain the lost ground that has been seized?
Although the dawn is bright and full of hope, the road ahead of the water battery may still be long and difficult, like in the middle of the water. At present, the cadmium anode with the highest energy density has a cycle life of more than 300 times and an energy efficiency of 78%, but it is still insufficient compared with lithium-ion batteries, and cadmium is rarer and more toxic, so it is necessary to find other anode materials. The use of vanadium anode, although the cycle life is more than 1000 times, which is similar to that of lithium-ion batteries, the energy density may not be satisfactory.
Crucially, while the voltage of this aqueous battery has increased, it only reaches about 2V, while lithium-ion batteries can typically reach 3.0 to 4.2V. And all these results are still only preliminary data in the laboratory, so there may be a long way to go for aqueous batteries to replace lithium-ion batteries.
Of course, you should not be completely pessimistic, because there have been previous studies to expand the electrochemical window of aqueous batteries to 3.23V by adjusting the composition of the electrolyte or additives, which is the progress made by the HE-E01 group of the Huairou Research Department of the Institute of Physics of the Chinese Academy of Sciences/Beijing National Research Center for Condensed Matter Physics in 2022.
In their paper, the Dalian team argues that this research has the potential to develop safe and high-energy-density aqueous batteries, providing new development options for grid-scale energy storage and even electric vehicles.
The study was published April 23 in the journal Nature Energy.
参考：Reversible multielectron transfer I−/IO3− cathode enabled by a hetero-halogen electrolyte for high-energy-density aqueous batteries