NaFePO4 Battery

https://sci-hub.se/10.1007/s12274-018-2139-0

"Low-cost room-temperature sodium-ion batteries (SIBs) are expected to promote the development of stationary ene rgy storage applications. However, due to the large size of Na+, most Na+host structures resembling their Li+ counterparts show sluggish ion mobility and destructive volume changes during Na ion (de)intercalation, resulting in unsatisfactory rate and cycling performances. Herein, we report a new type of sodium iron phosphate (Na0.71Fe1.07PO4), which exhibits an extremely small volume change (~ 1%) during desodiation."

"Impressively, capacities of 91 and 77 mA·h·g−1 can be rapidly charged within periods as short as 105 and 36 s."

"Remarkably, NFP/C showed capacities of 87 and 78 mA·h·g−1 at even higher discharging rates of 3,100 and 7,750 mA·g−1, respectively. When the current density returned to 15.5 mA·g−1, the capacity reversibly reached 140 mA·h·g−1."

"The average Coulombic efficiency was evaluated to be as high as 99.48% during the cycling test. To our knowledge, such extraordinary results have not been reported for Fe-based electrodes in SIBs, suggesting that it is an excellent candidate cathode material for long-life and high-rate SIBs"

Reagants Needed:

Ferrous sulfate heptahydrate, [Iron(II) sulfate heptahydrate]
Phosphoric Acid
Ethylene Glycol
L-ascorbic acid (vitamin c)
Distilled Water
Argon
Conductive Carbon (Ketjen black)
Carbon-coated aluminum current collector
Polymer Battery Separator
Polyvinylidene fluoride (PVDF)
1-methyl-2-pyrrolidinone (NMP)
NaDFOB (sodium difluoro(oxalato)borate)
Propylene carbonate
Fluoroethylene carbonate
Sodium Metal Foil

Tools Used:

Hot Plate with Stir Bar
Argon Gas
Autoclave and/or Temp controlled oven
Vacuum Drying Chamber
Aqueous Chemistry Glassware
Milligram Scale & Graduated Cylinder

Experiment:

Production of Sodium Iron Phoshate:

10 mmol of FeSO4·7H2O and H3PO4 (phosphoric acid) dissolved in

5mL of H2O (distilled water)
25mL ethelene glycol
400 mg L-ascorbic acid (vitamin-c) as reducer

Then,

30 mL of a 1 mol·L−1 NaOH ethylene glycol solution was introduced under continuous magnetic stirring and argon protection to form a light suspension. The solution was stirred further for 15 min before being transferred into a 100 mL Teflon-lined stainless steel autoclave. Then, the autoclave was kept at 180 °C for 10 h. Afterwards, the as-obtained NFP was filtered, washed with distilled water and acetone several times, and dried at 60 °C in a vacuum oven.

Desodiation of Sodium Iron Phosphate:

Na0.71Fe1.07PO4 was chemically desodiated by K2S2O8 (potassium persulfate) in an aqueous solution. Into 50 mL of a solution containing 0.4 g of K2S2O8, 0.5 g of NFP was introduced, and the resulting solution was stirred for 24 h.

Making Carbon Paste

NFP/C composites were obtained by ball milling the products with conductive carbon (Ketjen black) at a

ratio of 75:20, followed by heating at 450 °C for 2 h under an argon atmosphere.

Making Battery Electrode:

Charge/discharge tests were carried out using coincell-type cells (CR-2032); each cell consisted of an

NFP/C-based working electrode and a Na counter electrode separated by a glass fiber membrane. To

prepare the working electrode, NFP/C and polyvinylidene fluoride (PVDF) were mixed at a weight ratio

of 95:5 with 1-methyl-2-pyrrolidinone (NMP) serving as the solvent to obtain a slurry. After the slurry was coated onto a carbon-coated aluminum current collector, the electrode was dried at 110 °C under vacuum for 10 h.

Making Electrolyte:

NaDFOB (sodium difluoro(oxalato)borate) electrolyte dissolved in propylene carbonate (PC) and 5% fluoroethylene carbonate with a concentration of 1 mol·L−1

Making Battery:

Sodium Electrode (anode) | separator | SIP cathode on current collector

~j0ule