Project leader Gints Kucinskis

Agreement No

Research application No

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

April 1, 2022

Two research papers have been prepared and submitted, these are on electrochemical impedance spectroscopy and conductivity of Na2FeP2O7 and on synthesis and electrochemical performance of Na2FeP2O7/reduced graphene oxide composite. Electrochemical measurements of Na0.67Ni0.25Mn0.75O2 with and without protective coatings finalized, and the research mobility at Baden-Württemberg Center for Solar and Hydrogen Energy Research has been finished.

January 1, 2022

Two research papers have been published – on synthesis and electrochemical performance of Na2FeP2O7 ( synthesis of Na0.67MnO2 and its electrochemical performance as a function of the binder used ( Electrochemical impedance spectroscopy measurements of Na2FeP2O7 bulk material and electrodes in half-cells have been analysed. Na2FeP2O7/reduced graphene oxide has been synthesized and measured to determine the optimal reduced graphene oxide content. Synthesis of Na0.67Ni0.25Mn0.75O2 with and without protective coatings has been continued.

October 1, 2021

The amendments requested by the reviewers to the article on the electrochemical properties of Na2FeP2O7/C as a function of the carbon coating and the electrolyte used in the cell have been submitted. Participation in two scientific conferences - The 14th International Symposium on Systems with Fast Ionic Transport and the 72th Meeting of the International Society of Electrochemistry.

Synthesis of Na0.67Ni0.25Mn0.75O2 with and without protective coatings was performed, which would improve the stability of electrode materials in the electrochemical cell. Synthesis of Na0.67Fe0.43X0.07Mn0.5 (X - Cu, Al, Si, Mg), analysis of structure and electrochemical properties for screening of the best candidates for improved stability were performed. XRD measurements of Na2FeP2O7/C as a function of state of charge have been started.

July 1, 2021

Two scientific articles have been submitted: (1) on the electrochemical properties of Na2FeP2O7/C as a function of the carbon coating and the electrolyte used in the cell, and (2) on the electrochemical properties of Na0.67MnO2 as a function of the binder used. Detailed electrochemical and structural measurements for both materials were continued, as well as in-depth electrochemical impedance spectroscopy measurements for Na2FeP2O7. Research mobility started in the Baden-Württemberg Center for Solar and Hydrogen Energy Research.

April 8, 2021

Synthesis of Na2FeP2O7/C optimized, obtaining 93 mAh/g capacity (96 % of theoretical value). Extended analysis of Na2FeP2O7/C/rGO composites performed, analyzing various contents of carbon and their influence on electrochemical peroperties. Electrochemical measurements were carried out using 1 M NaClO4 salt in propylene carbonate as electrolyte with and without 5 wt.% fluoroethylene carbonate (FEC) electrolyte additive for stabilizing solid electrolyte interphase. The use of FEC benefits rate and cycling performance in half-cells. Manuscript of a research paper prepared on the subject.

January 7, 2021

Electrochemical cell with liquid electrolyte and no separator prepared for charging and discharging electrodes before ex-situ analyses. PVDF and alginate binders analysed as an alternative route for improving rate capability and cycle life of Na2/3MnO2 electrodes. Processing of Na2/3MnO2 in aqueous slurry with Na alginate is found to degrade Na2/3MnO2 because of protons and ultimately water intercalating between the transition metal – oxygen layers. PVDF binder in combination with FEC electrolyte additive is found to improve cycle life.

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.