Beginning on July 18, Zhengzhou, Henan Province encountered extremely heavy rainfall. During this period, a piece of news attracted the attention of many people: it was a new energy vehicle with half of its body submerged in water. It moves forward like a submarine in the water. In the end, the vehicle successfully drove out of the flooded area.

The elemental properties make lithium so popular

The reason why new energy vehicles can travel in deep water areas is actually easy to explain: because they do not need to obtain lithium from the outside air like fuel vehicles. Obtain oxygen as the oxidant required for energy release reactions. Inside the new energy vehicle battery pack, ions shuttle between the cathode and anode, generating current to release energy. Therefore, the "high-voltage system" of new energy vehicles can be completely isolated from the external environment and generally meets the IP67 waterproof standard, which means it can guarantee no water leakage under a water depth of 1 meter for 30 minutes.

However, the "low-pressure system" of new energy vehicles often does not have such excellent waterproof performance, and short circuits and other problems are prone to occur in the water, so it is still not suitable to drive in deep water areas where the tires are not covered.

New energy vehicles have "showed off" in front of the public with their superior water wading performance compared to fuel vehicles. And just like a famous saying in the industry, "Whoever wins the battery wins the world," power batteries, a core component that accounts for about 40% of the manufacturing cost of new energy vehicles, are also on the verge of undergoing huge changes.

This makes CATL, which has won the global championship of power battery market share for four consecutive years, still not dare to relax. It recently released its latest research and development of sodium-ion batteries. So, why does CATL, a lithium-ion battery giant, release sodium-ion batteries at this time? What advantages does it have compared with traditional lithium-ion batteries? Where is the future of power batteries?

In fact, the scientific community’s research on sodium batteries started almost at the same time as lithium batteries. Both started from the urgent need for new energy storage materials in the context of the Cold War and oil crisis in the late 1960s.

The first generation of lithium batteries were lithium metal batteries, which were different from current lithium-ion batteries. The crystallization effect during the charging process is extremely serious and can easily cause internal short circuits, so they are basically non-rechargeable batteries.

The essence of an ion battery is that metal elements shuttle back and forth between the positive electrode and the negative electrode in an ionic state. In the process, electrons are obtained and released, thereby forming an electric current. Metal ions are only "porters" of electrons, which results in almost no loss of positive and negative electrode materials and achieves a very high cycle life. This is the main idea behind rechargeable batteries now.

An ideal rechargeable battery needs to be as small as possible in size and weight, and to store and transport more energy. Therefore, from the perspective of the periodic table of elements, in order to become a good energy carrier, the relative mass of an atom must be small, the ability to gain and lose electrons must be strong, and the electron transfer ratio must be high. Lithium, the lightest metal on earth, has become the most ideal material for making batteries.

At the same time, sodium and potassium, lithium’s congeners, have also become the subject of research. But because sodium atoms have 8 more electrons than lithium atoms, the atomic radius of sodium is much larger than that of lithium. This means that it takes up more space when it is embedded and extracted between the positive and negative electrode materials, and requires a material with larger and stronger embedding holes than the positive and negative electrodes of lithium-ion batteries.

And it is much heavier than lithium, which makes sodium batteries have a lower energy storage density than lithium batteries. This series of problems made sodium-ion batteries once forgotten in the wave of battery research. Lithium batteries ushered in a technological breakthrough in the late 1980s. Lithium-ion-based "rocking chair batteries" replaced the previous lithium metal battery system, completely occupying the consumer electronics market in just a few decades and becoming a Today's mainstream solution for new energy vehicle power batteries.

Worry about "energy storage exhaustion"

But the first scientists who studied lithium batteries 50 years ago probably would not have thought that the earth is not a planet rich in lithium resources. The content of lithium in the earth's crust only accounts for 0.0065%, and 70% is in South America, causing uneven distribution.

A similar problem is that the situation of cobalt, another indispensable element in the cathode of lithium-ion batteries, is not optimistic.

It is mainly distributed in the Democratic Republic of the Congo (52%) and Australia (17%), accounting for 0.001% of the crustal mass. Globally, the production of lithium batteries continues to reach new highs and the overall price of lithium batteries has dropped sharply. However, the prices of raw materials used to produce lithium battery electrodes have soared rapidly; "exhaustion of reserves" is becoming a real concern for many people in the industry. Deep concern.

Lithium-ion batteries face a challenge that most commodities will never encounter: as production increases, prices not only fail to continue to decline, but may rise sharply. This situation has put new energy car companies on pins and needles, as the raw materials equivalent to hundreds of mobile phone batteries are used to build one car.

So in recent years, what major new energy vehicle companies have done most besides building cars is probably to reduce the content of lithium and cobalt in battery packs, acquire shares in upstream mineral mining companies, and vigorously Develop next-generation energy storage systems other than “lithium”.

Against this background, sodium-ion batteries, which had been neglected in the early years, suddenly became a research hotspot after 2010. Unlike lithium, which is scarce in reserves, sodium accounts for 2.75% of the mass in the earth's crust, which is 400 times that of lithium. As the main component of table salt on our daily tables, the price of sodium chloride is less than 1/10 of that of lithium carbonate.

“Sodium-lithium hybrid”

As the world’s largest new energy vehicle market, China is also a world leader in sodium-ion battery research. Before the Ningde era, the sodium-ion battery researched by Zhongke Haina, a subsidiary of the Institute of Physics of the Chinese Academy of Sciences, was put into mass production last year, but the energy density was still low, around 145Wh/kg.

The cell energy density of the first-generation sodium-ion battery in the CATL reached 160Wh/kg. Although the energy density of 160Wh/kg is not high compared to ternary lithium batteries that can easily reach 300Wh/kg, and is even lower than lithium iron phosphate batteries, it is already the highest energy storage density of sodium-ion batteries in the world. level.

In addition, CATL’s sodium-ion battery can reach more than 80% of the battery when charged for 15 minutes at room temperature; and in a low temperature environment of -20 degrees Celsius, it also has a discharge retention rate of more than 90%, which is much better. The performance of ternary lithium batteries is less than 70% under this condition.

Sodium-ion batteries can also pass the industry's most stringent acupuncture test and can basically be regarded as the "fast charge" and "low temperature performance enhanced" version of lithium iron phosphate batteries. Supplemented by extremely high safety and cost advantages, sodium-ion batteries can be used as a substitute for lithium iron phosphate batteries and are widely used in many fields such as low-end electric vehicles, commercial electric buses and even two-wheeled battery vehicles.

At the press conference, CATL also proposed a technical solution for mixing sodium-ion batteries and ternary lithium batteries at a ratio of 2:1, using excellent BMS (battery management system) logic to accurately control the two batteries. The discharge level curve makes it possible for sodium-ion batteries to be installed on high-end electric vehicles with more stringent endurance requirements.

Multiple technical solutions emerge

According to the country’s vision of carbon emissions peaking in 2030 and achieving carbon neutrality in 2060, the demand for clean energy such as solar and wind energy in the west is also increasing. expand further. However, unlike thermal power, clean energy can dynamically adjust power generation according to load. If the generated power is not used in time, it can only be treated as "abandoned power".

It is understood that in 2018, my country abandoned light, wind, and water electricity totaling 102.2 billion kWh, which is really a huge waste. In order to stably connect the electricity generated by clean energy to the power grid, large-scale "energy storage power stations" must be established.

Take the country's largest pumped storage power station built in Yangjiang, Guangdong some time ago as an example. Its basic principle is to use the excess electricity during the urban power peak period to pump water. After the water is pumped to a high place, The water is then released to generate electricity during peak power consumption periods. This can be regarded as a giant rechargeable battery that undertakes tasks such as peak shaving, valley filling, and emergency backup in the power grid.

Such a task can also be accomplished by sodium-ion batteries that are low-cost, relatively high in energy density, and insensitive to ambient temperature.

So, are sodium-ion batteries the future of new energy vehicles? In fact, the current mainstream power battery solutions for new energy vehicles, including ternary lithium batteries and lithium iron phosphate batteries, all fall into the category of "liquid batteries", which require liquid "electrolyte" as a medium for ions to travel unimpeded.

In fact, there is another "solid-state battery" solution for power batteries that is about to be put on the market. As the name suggests, it uses an electrolyte that is solid at room temperature as a medium to transfer ions. It is generally believed that the upper limit of energy storage density of liquid batteries is 350Wh/kg, while the energy density of solid-state batteries is expected to reach 1000Wh/kg.

Solid electrolytes are very stable and basically eliminate the risk of thermal runaway explosion. They are considered by the industry to be the development direction of future power batteries. Many domestic battery manufacturers have also been deployed on this track for many years. At present, theoretical research papers on new materials for solid-state batteries are also blooming everywhere. I believe that the era of solid-state batteries is not far away from us.

Previously, the new energy vehicle industry had made a bold prediction that the turning point for new energy vehicles to completely replace fuel vehicles would come when the energy density of power batteries reaches 400Wh/kg. At present, many countries in the world have also announced that 2030 will be the time node for a complete ban on the sale and production of fuel vehicles.

I would like to end the article with a sentence from CATL founder and chairman Zeng Yuqun at the sodium-ion battery launch conference: "We believe that the world of electrochemistry is like an energy Rubik's Cube, and the unknown is far greater than the Known. "I believe that mankind will eventually overcome various difficulties in the development of power batteries and bring the world into the era of clean energy.

Author | Ma Dianqiu

Produced by Kanshijiazhi New Media