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Introduction to NFPP (Sodium-ion) batteries and comparison with LFP (Lithium-ion)

Sodium-ion batteries are also known as Na-ion batteries, NIB, or SIB. Their construction technique is very similar to that of Lithium-ion batteries, which consist of a metal salt-based cathode, a carbon-based anode, a polyolefin-based separator, and a liquid electrolyte.

Na4Fe3(PO4)2P2O7, also known as NFPP, is a polyanion type of Sodium-ion cathode active material gaining popularity, and it is expected to compete with LFP Lithium-ion batteries. Low-cost polyanion type based LFP cells have taken over the low-range and mid-range EV and ESS markets over the past few years. NFPP cells are expected to capture a good market share in various applications, potentially taking some of the market share from LFP cells.

Nominal voltage, also understood as the average voltage delivered during discharge, is lower for NFPP than LFP. This will sometimes require changing the number of cells arranged in series in the battery pack to work the operating voltage of the existing motor controller in EVs and inverters for energy storage projects.

Initial prototypes and pilot production by Sodium-ion cell manufacturers using NFPP material are able to achieve around half the ampere-hour discharge capacity with the same cell form factor. For example, a typical prismatic 314Ah LFP cell with the same dimensions in the NFPP type is able to have around 160Ah discharge capacity. NFPP cells are expected to have better maximum continuous charge and discharge current rating than LFP cells. They are also expected to have better pulse peak current rating for charge and discharge compared to LFP cells.

NFPP cells can charge at lower temperatures than LFP cells; NFPP cells can charge up to -10°C, whereas LFP cells can charge until 0°C only. This helps Sodium-ion cells to become a safer alternative to NMC batteries that can operate below 0°C but have safety issues.

The internal resistance of Sodium-ion cells is lower than that of Lithium-ion cells for the same ampere-hour discharge capacity. NFPP cylindrical cells somewhat have a similar cycle life compared to LFP cylindrical cells at the moment.

  • Sodium-ion cells follow the same working mechanism as traditional Lithium-ion batteries, in which sodium ions move from cathode to anode during charging and anode to cathode during discharging. The movement of metal ions happens in a similar way, which is through the liquid electrolyte medium.
  • The manufacturing process is very similar to that of lithium-ion batteries, i.e., cathode slurry and anode slurry coated on current collectors and dried in the oven. These electrodes are sandwiched by using a separator, put in a case and filled with liquid electrolyte and sealed.
  • Sodium-ion cells are adopting similar form factor with similar dimensions such as Lithium-ion cells. For example, some dimensions of LFP prismatic cells are being adopted by Sodium-ion cell manufacturers. This is to allow easy adoption of the cells with respect to dimensions.
  • Sodium-ion batteries use aluminium for both positive and negative current collectors. In contrast, lithium-ion batteries use aluminium only for the positive current collector, and copper is used for the negative current collector. Since aluminium is cheaper, it brings down the cost.
  • Sodium-ion batteries have a wider range of operating voltage and have no problems being in an extremely low voltage state for a long duration. It makes shipping at low voltage possible.
  • Sodium-ion batteries can provide better discharge output in negative temperature operation, thereby removing the need for heating systems.
  • Sodium-ion batteries are expected to work until lower SoH before they reach end-of-life.
  • Ability to charge faster (Higher C rate of charge)
  • Ability to provide high power (Higher C rate of discharge)
  • Considered to be safer due to higher stability
  • Considered to be more durable and expected to have a longer cycle life
  • Works in a wide range of higher and lower operating temperature conditions
  • The cost of Sodium-ion batteries is expected to be lower in the future.
  • The existing market price is higher and needs time to reach good volume production in order to be lower than LFP cells at per kWh level.
  • Volumetric energy density is poorer than LFP cells, making it difficult to fit in a given space where LFP cells are fitting, and this can be crucial in EV usage.
  • Gravimetric energy density is poorer than LFP cells, making the battery pack heavier than LFP battery packs, and hence, it becomes discouraging for mobile applications such as EVs.
  • The cost of Sodium-ion batteries is higher due to a lack of high-volume production.
  • Sodium-ion batteries are not suitable for long-range electric cars, and they are not suitable for the BESS race in which every company is trying to fit as much capacity as possible in a standard 20-foot container.

Rahul Bollini is an R&D expert in Lithium-ion cells with 9 years of experience. He founded Bollini Energy to assist in deep understanding of the characteristics of Lithium-ion cells to EV, BESS, BMS and battery data analytics companies across the globe. Rahul can be reached at +91-7204957389 and bollinienergy@gmail.com.

Also read: Understanding energy storage systems for commercial & industrial (C&I) applications | Part 2

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