Systematic Tuning of the High Voltage Spinel LiNi0.5Mn1.5O4 By Modification of the Precursor and the Thermal Treatment
Authors: Seidel Matthias , Nikolowski Kristian , Kinski Isabel , Wolter Mareike , Michaelis Alexander 
Published: February 2020

To further increase the effectiveness of lithium ion batteries an improvement especially in the energy density of the system is needed. High voltage cathode materials are a possible solution for solving this challenge. One potential high voltage material is LiNi0.5Mn1.5O4, which despite of its promising properties, has not been commercialized yet. A requirement for the commercialization of the cathode material is a systematic understanding of synthesis condition and their influence on the material properties. There are several synthesis routs described, which produce a precursor from acetates, nitrates, carbonates, sulfate or hydroxides, by solid-state, precipitation, sol-gel or spray trying for example and afterwards apply different temperatures and durations while the calcination of the  precursor. All synthesis steps influence the properties of the material which leads into different electrochemical features for capacity, performance and cycle life. Therefore it is very hard the compare all the different synthesis routs and evaluate a systematic correlation. In my presentation I will show a chemical and procedural approaches, which not only will help to improve the electrochemical properties of LiNi0.5Mn1.5O4, but also can be scaled into an industrial dimension and focus on the variation of parameters which have not been discussed in full detail yet.

There are several factors, which influence the electrochemical properties of LiNi0.5Mn1.5O4. Two of those are the amount of manganese(III) in the cathode material and a electrochemical inactive impurity phases. One important factor of influence for the formation of the manganese(III) content in LiNi0.5Mn1.5O4 and an impurity phase, which often consist of NixO and/or LixNi1-xO, is the oxygen content at the sample while the temperature treatment. [1] We used two different approaches to control the oxygen amount at the sample while the calcination. A chemical and a procedural approach where chosen. For the chemical method precursors with different composition of nitrate and acetate salts were used, which therefore changes the chemical composition of the precursor. Those salts show different gas removal at high temperature and therefore lead to a different environment for the sample while the calcination. For the procedural approach different kinds of calcination environments where used. By using a rotary kiln for example the resulting gas is removed similar for all the samples no matter the precursor used in comparison to a Muffle furnace.

In our presentation we will present, that by changing the precursor chemistry the manganese(III) amount and the amount of impurity phase of the product can be tinkered. We will show, that the products exhibits a very different shape after the first calcination and therefore a different surface area. A different surface area means a different oxygen content at the sample. Resulting from this fact we will indicate the influence on the manganese(III) amount and the impurity phases. To achieve a systematic understanding all the synthesis materials were analyzed by electrochemical measurements, which will focus around capacity, cycle life and performance.  The manganese amount will be calculated from the discharge curve, the impurity phase was analyzed by XRD measurements. Furthermore the samples were characterized by SEM, RAMAN to achieve information about the space group and BET to obtain information about the surface area of the samples. Furthermore we will show how to reduce the influence of those shapes by controlling the gas removal over using a rotary kiln. Resulting from this outcome the chemical and procedural approach can improve the electrochemical properties with rather easy ably able methods, which can be scaled into an industrial format.

Acknowledgment

The authors wish to thank for financial support by the BMBF (Bundesministerium für Bildung und Forschung) within the BaMoSa (Batterie – mobil in Sachsen) project.

 [1]Pasero, D. Reeves, N. Pralong, V. & West, A. R., J. Electrochem. Soc.
155, A282 (2008).