Lithium batteries used in electric vehicles are expensive, which is one of the reasons why electric vehicles are difficult to popularize. Now battery technology is expected to achieve a breakthrough! Future electric vehicles may be able to replace lithium batteries with low-cost and resource-saving sodium ion batteries.
Electric vehicles - especially those that use renewable energy to generate electricity - are seen as a future model that will contribute to global climate protection. However, for many years, the rare and relatively expensive lithium has been used in the battery technology by car manufacturers, which has slowed down the pace of large-scale popularization of electric vehicles in the world.
Although electric vehicles, commercial vehicles or electric bicycles are developing in full swing, the scope of their use is limited. The high price, cumbersome charging facilities and the battery production process which consumes a lot of raw materials hinder the rapid development of electric vehicles. For electric vehicles to be widely used, automakers must introduce more durable, more sustainable and cheaper batteries.
Sodium ion battery may be a feasible solution, and the research and development of sodium ion battery has also made remarkable progress recently. In the foreseeable future, sodium ion batteries will replace lithium batteries in electric vehicles, smart phones or notebook computers.
Lithium and sodium, two alkali metals, have very similar chemical properties. Although the energy density of sodium is lower than that of rare lithium, it is easier to obtain sodium and its price will be relatively low.
At present, the performance of sodium ion battery is still about 20 years behind that of lithium battery. The reason is that researchers have only focused on developing more powerful lithium in the past decade or so.
But now there are not only groundbreaking scientific publications, but also a lot of forward-looking prototypes: according to a report published in May, the capacity of a sodium ion battery developed in South Korea only dropped to 80% of its original capacity after about 500 complete charging cycles. Another battery, developed by a U.S. - Chinese research team, can complete about 450 charges at the same battery capacity. Although the capacity of a Chinese made sodium ion battery is small, it still has 70% of the battery capacity after 1200 times of 12 minutes fast charging.
It may not sound like much, but in actual use, these batteries may be able to withstand a higher number of charges, because in daily life, the battery is not usually used up before charging. In the experiment, the complete discharge and charging will cause more battery loss.
The metal element lithium is rare and expensive, but most of the current battery technology uses lithium battery.
In addition, sodium ion technology does not need to use scarce resources: the cathode does not need rare lithium salt, as long as edible salt is enough. High performance anodes can be made from lignite, wood and other biomass. Cobalt or similar rare substances are not required in the production process.
Breakthrough basic research?
Sodium has two disadvantages: it weighs three times as much as lithium, so even though lithium accounts for less than 5% of the total battery weight, a sodium ion battery is still heavier than a lithium battery.
In addition, the performance of sodium battery is weak. Because the capacity of sodium ion is 0.3V less than that of lithium battery, it will inevitably lose about 10% energy density. Most importantly, the graphite anode of the current battery can not hold enough sodium.
According to a report published by the German Russian working group led by the Helmholtz Research Center (hzdr) in Dresden, Germany, nano carbon can help to improve the problem. The report points out that the use of ultra-thin carbon double-layer graphene can store more sodium ions than graphite in the anode.
If the graphite anode can be replaced in the future, the graphene electrode can be installed in the lithium battery, which may significantly improve the capacity of the battery.
"It's like putting a ball between two pieces of paper," said krashenningkov, a physicist at hzdr. Constantly add small balls between the paper, the paper will be pushed more and more open, the gap between the two papers will be increased. "
The same technology?
If the lithium battery with multilayer structure is feasible, can it also be applied to other alkali metals such as sodium? A team from Dresden, Stuttgart and Moscow wanted to use sophisticated supercomputer simulations to find out. Because the prototype of sodium ion battery has not operated smoothly, the reason is that sodium can only enter the graphite anode.
The calculation results show that sodium, like lithium, can be embedded between graphene layers in a multilayer structure.
If graphene electrode is replaced by graphite anode in the future, it may achieve higher storage capacity.
These results may provide a breakthrough for the development of low-cost sodium batteries. "Our work is purely theoretical and we do not advocate the development of a new generation of batteries in the foreseeable future based on this research," krasheninkov said. But maybe our research can provide interesting new ideas for engineers. "
Happily, sodium ion battery is no longer just a theoretical concept. A breakthrough in related technologies seems to be in sight.
The latest research results show that there are feasible, reasonable and resource-saving alternatives to replace expensive lithium batteries, and even improve their performance through multilayer structure.
It must be some time before the sodium ion battery technology is complete, mass-produced and used in electric vehicles or mobile phones. However, once the time is ripe, due to the relatively similar technology, there should be no big problem in converting the production line from lithium battery to sodium ion battery.