Researchers at the US Department of Energy’s (DOE) Argonne National Laboratory have invented and patented a new cathode material for sodium-ion batteries (SIBs).

Our battery program at Argonne has been studying sodium-ion batteries for well over a decade now. And our design for the cathode structure makes sodium-ion batteries an appealing alternative for budget-friendly and more sustainable electric vehicles.

—Christopher Johnson, senior chemist and Argonne distinguished fellow

In an open-access 2022 review paper published in Energy Science & Engineering, a team from Boise State University and Argonne explained that:

Sodium based LTMOs [layered transition metal oxides] with composition Na_xTMO₂ (TM = transition metal, e.g., Ni, Fe, Mn, Co, 0.0 ≤ x ≤ 1.0) are attractive positive electrode materials for SIBs due to their combination of high voltage, high theoretical capacity, and dense structure. Compared to lithium based LTMOs, sodium is electrochemically active with more of the 3d transition metal elements. The larger size of Na enables structures that are unstable in Li-based LTMO materials. The versatile combination of elements and structures in sodium based LTMOs provides many routes to tune their properties.

—Gabriel et al.

The innovation by Johnson’s research team, funded in part by the Vehicle Technologies Office of the DOE Office of Energy Efficiency and Renewable Energy, stems from his prior research with two other Argonne Distinguished Fellows—Michael Thackeray (retired) and Khalil Amine—on a lithium nickel-manganese-cobalt (NMC) oxide cathode material with a structure in which the atoms are arranged in layers. This structure allows easy insertion and extraction of lithium ions between the layers. These ions thus can move freely from the cathode to anode and back to charge and discharge the battery.

Drawing insights from the earlier research, Johnson’s team invented a layered oxide cathode tailored for sodium-ion batteries. This variation on the NMC cathode is a sodium nickel-manganese-iron (NMF) oxide with a layered structure for efficient insertion and extraction of sodium. The absence of cobalt in the cathode formula mitigates cost, scarcity and toxicity concerns associated with that element.

The team’s interest in sodium-ion batteries stems from their many advantages. Two are sustainability and cost. Sodium is far more naturally abundant and easily mined than lithium. It is thus a fraction of the cost per kilogram and much less susceptible to price fluctuations or disruptions in the supply chain.

Our estimates suggest that a sodium-ion battery would cost one-third less than a lithium-ion one.

—CHristopher Johnson

Furthermore, besides sodium, the cathode material predominantly contains iron and manganese. Both elements are globally abundant and not on the endangered list.

Another benefit is that sodium-ion batteries can retain their charging capability at below freezing temperatures. This addresses one of the notable drawbacks of existing lithium-ion batteries. Also working in favor of sodium-ion batteries is that the technology for battery management and manufacturing already exists. This is because their design closely resembles that of lithium-ion batteries.

However, sodium metal is about three times heavier than lithium, and that adds considerably to the battery weight, Johnson explained. The additional weight translates into a shorter driving range.

To date, this shortcoming has hindered sodium-ion batteries from making inroads into the electric vehicle market. Compared with other sodium-ion technology, however, the team’s cathode has much higher energy density, enough to power electric vehicles for a driving range of about 180-200 miles on a single charge.

Johnson emphasized that while the sodium-ion battery might not appeal to those seeking long driving ranges, it could attract budget-conscious consumers, particularly urban dwellers whose daily driving rarely exceeds this distance.

Another shortcoming of earlier sodium-ion batteries is a short cycle life. But with the team’s cathode material, battery cells can be charged and discharged the same number of cycles as their lithium-ion counterparts.

We have now transitioned from the laboratory phase and are poised to subject our cathode to testing within battery cells similar to those in an actual electric vehicle battery. From there, we hope the NMF cathode will follow the trajectory of our NMC cathode and be chosen for manufacturing.

—Christopher Johnson

Testing will be done in Argonne’s Cell Analysis, Modeling and Prototyping Facility. The team is also working to develop different materials for the electrolyte and anode to boost energy density even further.

Resources

• Gabriel E, Hou D, Lee E, Xiong H. (2022) “Multiphase layered transition metal oxide positive electrodes for sodium ion batteries.” Energy Sci Eng. doi: 0.1002/ese3.1128