Sodium-Ion - Battery Design

Sodium-ion batteries operate analogously to lithium-ion batteries, with both chemistries relying on the intercalation of ions between host structures. In addition, sodium based cell construction is almost identical with those of the commercially widespread lithium-ion battery types. However, sodium-ion batteries are characterised by several fundamental differences with lithium-ion, bringing both advantages and disadvantages:

Advantages:

Environmental abundance: Sodium is over 1000 times more abundant than lithium and more evenly distributed worldwide.
Safety: Sodium-ion cells can be discharged to 0V for transport, avoiding thermal run-away hazards which have plagued lithium-ion batteries.
Low cost: Sodium precursors (such as Na₂CO₃) are far cheaper than the equivalent lithium compounds.
Three major families of materials for cathode chemistry options:
- layered transition metal oxides
- polyanionic compounds
- prussian blue analogs
Cathode materials can be synthesized from more sustainable transition metals such as Fe, Cu or Mn.

Disadvantages:

Sodium-ion cells have lower energy densities than lithium-ion. This is due to sodium being significantly heavier and larger than lithium, as well as Na⁺/Na having a higher reduction potential than Li⁺/Li.
Sodium-ion technology is not as well established as lithium-ion.

Sodium-Ion Battery Materials

Many of the battery components in both sodium-ion and lithium-ion batteries are similar due to the similarities of the two technologies. This post provides a high-level overview for the constituent cell parts in Sodium-ion batteries.

Sodium-Ion Cell Characteristics

An energy density of 100 to 160 Wh/kg and 290Wh/L at cell level.
A voltage range of 1.5 to 4.3V. Note that cells can be discharged down to 0V and shipped at 0V, increasing safety during shipping.
20-30% lower cell BOM cost than LFP.
A wider operating temperature than lithium-ion cells (-20°C to +60°C).
Typical Energy efficiency 92% at C/5.

Hard Carbon Anodes in Sodium-ion

Emerging battery technology – promising cost, safety, sustainability, and performance advantages over current commercialised lithium-ion batteries^1,2.
Advantages:
- widely available
- inexpensive raw materials
- rapidly scalable technology
- meeting global demand for carbon-neutral energy storage solutions^3,4.
Adding metals would increase the overall energy density, but results in volumetric changes leading to failure.

optimization of hard carbon for sodium ion - poster

Sodium-Ion Degradation

Over-voltage Charging
Presence of Hydrogen
- causes irreversible degradation of α-NaMnO₂ when used as the cathode in Na-ion batteries [1].
Defects in the Cathode Atomic Structure
- these form during the steps involved in synthesizing the cathode material. These defects eventually lead to a structural earthquake in the cathode, resulting in catastrophic performance decline during battery cycling [2].