Advanced Materials for Sodium Ion Batteries (2019 - 2022)

Project leader Gints Kucinskis

Agreement No 1.1.1.2/16/I/001

Research application No 1.1.1.2/VIAA/1/16/166

The aim of the project is to improve performance of electrode materials for sodium ion batteries. Two materials for sodium ion batteries are studied within this research project: NaMO2 and Na2MP2O7 (M – Fe, Mn or combination of both). The materials are synthesized, their structure, composition, morphology and electrochemical properties are being analyzed along. We study reduced graphene oxide as an additive for improved electrochemical properties. Electrochemical properties are studied as a function of NaMO2 and Na2MP2O7 phase transitions in equilibrium and non-equilibrium conditions. The result of this project will be an improved cycling stability and power density of the studied sodium insertion materials.

Project is being carried out at Institute of Solid State Physics, University of Latvia for 36 months starting from 01.04.2019. until 31.03.2022. The total costs of the project are 133 805.88 EUR.


 

Project progress

October 19, 2020

NaMO2 and Na2MP2O7 (M – Fe, Mn) cathode materials for sodium-ion batteries have been prepared and characterized. Their composites with reduced graphene oxide and other carbon nanostructures have also been studied. As planned, Na2FeP2O7 has been prepared, its composites with carbon coating and reduced graphene oxide (rGO) have been studied, improving the rate capability of the material. Carbon coating has been studied on α-NaFeO2 and found to not improve the rate capability or cycling stability of the material, with further processing options limited due to its instability in water. It was also found that the cyclability and rate performance of Na0.67MnO2 is more improved by replacing polyvinylidene fluoride (PVDF) binder with Na alginate than by introducing nanostructured carbon additives (carbon nanotubes).

As planned, an electrochemical cell for in-situ measurements of selected battery materials has been appropriated for use on the in-house equipment (cell-holder made, initial testing of the cell done). With the experimental setup complete, it is now planned to carry out in-situ XRD experiments on at least two of the developed materials, likely Na2FeP2O7 and Na0.67MnO2.


June 26, 2020

Synthesis of Na2FeP2O7 and NaFeO2 was optimized: synthesis, structural analysis, electrochemical measurements. The holder of in-situ XRD diffraction cell has been prepared, first measurements to be expected in the coming weeks. Bachelor’s thesis on synthesis and physicochemical properties of Na2FeP2O7 and Na2FeP2O7/C/reduced graphene oxide has been defended.

April 3, 2020

The synthesis of NaFeO2 un Na2FeP2O7 sodium-ion battery cathodes has been optimized. Na2FeP2O7 electrochemical properties have been characterized as a function of carbon content added to the synthesis. The discharge capacity of Na2FeP2O7 /C composite was up to 82 mAh/g or 82 % of theoretical capacity, so the target capacity (≥80 % of theoretical capacity) is considered to be reached. Carbon coating allows avoiding impurities and leads to improved rate capability – 70 mAh/g at 1 C (1 C = 97 mA/g).


January 10, 2020

NaFeO2 un Na2FeP2O7 sodium-ion battery cathodes have been characterized electrochemically. α-NaFeO2 has been synthesized and shows signs of sodium insertion and extraction. The prepared Na2FeP2O7 is shows no impurities in x-ray diffraction measurements and has charge capacity of up to 73 % of theoretical (71 mAh/g of 97 mAh/g) as a result of glucose addition to the synthesis. Without glucose the charge capacity was only 53 % of the theoretical. The target is to reach more than 80 % of the theoretical capacity. The cell holder for in-situ x-ray diffraction measurements is 50 % ready, preparations for in-situ x-ray diffraction measurements are underway.


October 8, 2019

The previously prepared NaFeO2 un Na2FeP2O7 sodium-ion battery cathodes have been characterized electrochemically. It has been discovered that the prepared β-NaFeO2 is not electrochemically active, therefore synthesis of α-NaFeO2 has been begun. The prepared Na2FeP2O7 is chemically pure and displays electrochemical activity. So far, the measured charge capacity is roughly 50 % of the expected. We hypothesize that a higher charge capacity has not been measured due to large grain size and low electronic conductivity inherent to Na2FeP2O7. In order to avoid both in the final material, a new synthesis of Na2FeP2O7 has been performed by adding glucose to the precursors. Glucose decomposes into C, CO2 and H2O, the Na2FeP2O7 obtained has an increased carbon content. Additionally, the presence of carbon has previously been shown to lead to smaller grain size.


August 5, 2019

Relevant scientific literature was studied, the setup for synthesis of NaMO2 and Na2MP2O7 (M – Fe, Mn or Fe0.5Mn0.5) is built. First preparations for building an electrochemical cell have been done, 1 M NaClO4 electrolyte in propylene carbonate was prepared. Preparation of a sample holder for in-situ x-ray diffraction cell was started.

Na2FeP2O7 and NaFeO2 has successfully been synthesized, confirmed by x-ray diffraction results. Grain size according to scanning electron microscopy is 1 – 5 µm. First syntheses of analogue materials with Fe replaced by Mn has been started.