CATL recently announced a sodium-ion battery. Also, the battery manufacturer is working on a hybrid battery that combines lithium-ion and sodium-ion cells in a single battery pack.
Like lithium, sodium is one of the alkali metals, but is one row lower on the periodic table of the elements. Sodium ions are much larger than lithium ions, which can lead to problems with graphite anodes used in lithium-ion batteries.
Because there the cations between the carbon layers are built into the structure of graphite, just like books are placed on a shelf. If the books (ions) are too large, they no longer fit on the shelf. Or the shelf becomes so large that it no longer fits in the room - the energy density suffers.
According to CATL, the lower energy density of sodium-ion batteries has reduced interest in this technology in recent years. But it may be back as this battery chemistry has its own unique set of benefits.
CATL uses Prussian white for the cathode, a variant of the well-known Prussian blue dye. Chemically, it is iron hexacyanoferrate with the formula Fe4[Fe(CN)6]3). In Prussian White, some of the iron ions are replaced by sodium: NaxFey[Fe(CN)6]z. As with conventional lithium-ion batteries, the anode is made of carbon, not graphite, but a porous material.
The first generation sodium-ion cell from CATL should already have a decent energy density, charge quickly and offer almost the same capacity even at low temperatures as it does at room temperature:
- Energy intensity: up to 160 Wh/kg (second generation target: 200 Wh/kg);
- Charging: up to 80% SOC in 15 minutes at room temperature;
- Low temperatures: at -20 degrees, more than 90% of the storage capacity is retained.
According to CATL, the sodium-ion battery is superior to lithium iron phosphate (LFP) batteries in low temperatures, fast charging and life, but the energy density is currently even lower. Thus, CATL can be specifically designed for use in cold climates:
Another important advantage is that the sodium-ion battery can be manufactured at the same production facilities as lithium-ion cells. It is reported that CATL has already begun commercial production of new elements and plans to begin mass production in 2023.