Researchers at the Chinese Academy of Sciences said they have developed an electrolyte for an all-iron flow battery with little performance degradation even after more than 6,000 charge-discharge cycles. The team claims raw material costs could be up to 80 times cheaper than lithium-based batteries, drawing attention as a candidate for next-generation power grid storage.

CleanTechnica, an electric-vehicle-focused outlet, reported on April 28 local time that the findings were published in the international journal Advanced Energy Materials.

The study focuses on improving long-term stability, seen as the biggest weakness of all-iron flow batteries. All-iron flow batteries use iron-based electrolytes for both the cathode and anode. They have been repeatedly cited as candidates for large-scale power grid storage because raw materials are inexpensive and fire risk is low.

But previously, repeat charge-discharge life has been limited due to hydrogen gas side reactions at the anode, loss of active material and crossover between electrolytes.

The researchers explained that they reduced these problems by newly designing the structure of an iron-complex anode electrolyte. They said they simultaneously improved electrochemical stability and suppression of membrane permeation by applying a structure with large steric hindrance and a negatively charged protective layer.

The team designed 11 types of iron complexes based on 12 organic ligands and then selected a final electrolyte. It said an all-iron flow battery using the electrolyte maintained stable charge-discharge performance for more than 6,000 cycles at a current density of 80 mA cm−2.

Cost competitiveness is also drawing attention. Lithium carbonate, a key raw material for lithium-ion batteries, has traded between $7,000 and $80,000 per ton over the past 5 years, while ferrous sulfate, a raw material for all-iron flow batteries, can be secured relatively cheaply as an industrial byproduct.

But the 80-times lower cost presented by the researchers is limited because it is a comparison based on raw materials. Actual power grid storage deployment includes additional equipment costs such as ion-exchange membranes, pumps and power conversion equipment. In particular, whether the use of expensive ion-exchange membranes can be reduced is cited as a key variable for commercialization competitiveness. The industry says further verification is needed on whether the raw material cost advantage will translate directly into system price competitiveness.

The market is paying attention to the potential of all-iron flow batteries as demand grows for long-duration energy storage. Lithium iron phosphate (LFP) batteries currently lead the utility-scale storage market, but in the long-duration segment requiring power storage for several days or more, long life and low capital costs may matter more than energy density.

But the achievement remains at the laboratory stage. The researchers have not disclosed plans to build pilot facilities or a commercialization timeline. The currently disclosed 6,000-cycle life is also based on laboratory cells, and performance in kilowatt-scale or megawatt-scale systems could vary depending on factors such as thermal management, membrane fouling and current distribution.

The industry sees independent performance verification and operating results from demonstration facilities as key factors that will determine commercialization potential. It also says the low-cost structure of iron-based materials has the potential to change cost competition in the power grid storage market over the long term.