2.9 Redox Titration
31
acid and 75 % hydrochloric acid was added to dissolve the samples. The solutions
were then analyzed by Dan Chevalier (Minerals Engineering Centre, Dalhousie University) to give the concentrations of nickel, lithium and manganese, accurate to 5 %
for the small samples. The same method was used for bulk samples, though slightly
more powder was used to improve the precision of the measurements. For the starting
solutions used with the solution-processing robot, AA measurements were repeated
three times such that the uncertainty was 2 %.
2.8 Scanning Electron Microscopy
Scanning electron microscopy (SEM) allows the viewing of particles as small as
50 nm in length. As will be discussed in the next chapter, the crystallites made in
combinatorial samples heated to 800
◦ C typically fall in this range such that the SEM
was useful in order to get a better idea of whether or not phase separation had occurred.
To this end, a few samples were imaged by Ramesh Shunmugasundaram using a
Hitachi S-4700 field emission scanning electron microscope with an accelerating
voltage of 10 kV and an emission current of 15 μA.
2.9 Redox Titration
As mentioned in the introduction, the oxidation states of the transition metals in the
electrode material have a large effect on the electrochemistry. It proved useful to use
redox titrations in order to determine the average oxidation state of the nickel and
manganese for the materials discussed in Chap. 8. This involved two redox titrations,
both using potassium permanganate. The first involved adding the potassium permanganate to the samples (both dissolved in acid) in order to determine the total amount
of manganese present. The second titration involved first mixing the dissolved sample with ferrous ammonium sulfate in order to reduce nickel and manganese to the
2+ oxidation state while oxidizing some iron to 3+ state. The subsequent titration
with potassium permanganate then reduced iron back to 2+. The two measurements
allowed the determination of the average manganese oxidation state (assuming all
nickel was in the 2+ state). As such, a result for the manganese oxidation state
greater than 4.0 would imply some Ni
3+ was present. It is important to notice that
this method cannot distinguish between a Ni
2+ –Mn
4+ pair and a Ni
3+ –Mn
3+ pair,
since this approach essentially counts the number of oxidation states above 2+. To
make the distinction between these two combinations, manganese X-ray absorption
spectra were taken as described in the next section. The titrations were performed
by Oliver Schilling of Erachem Comilog.
31
acid and 75 % hydrochloric acid was added to dissolve the samples. The solutions
were then analyzed by Dan Chevalier (Minerals Engineering Centre, Dalhousie University) to give the concentrations of nickel, lithium and manganese, accurate to 5 %
for the small samples. The same method was used for bulk samples, though slightly
more powder was used to improve the precision of the measurements. For the starting
solutions used with the solution-processing robot, AA measurements were repeated
three times such that the uncertainty was 2 %.
2.8 Scanning Electron Microscopy
Scanning electron microscopy (SEM) allows the viewing of particles as small as
50 nm in length. As will be discussed in the next chapter, the crystallites made in
combinatorial samples heated to 800
◦ C typically fall in this range such that the SEM
was useful in order to get a better idea of whether or not phase separation had occurred.
To this end, a few samples were imaged by Ramesh Shunmugasundaram using a
Hitachi S-4700 field emission scanning electron microscope with an accelerating
voltage of 10 kV and an emission current of 15 μA.
2.9 Redox Titration
As mentioned in the introduction, the oxidation states of the transition metals in the
electrode material have a large effect on the electrochemistry. It proved useful to use
redox titrations in order to determine the average oxidation state of the nickel and
manganese for the materials discussed in Chap. 8. This involved two redox titrations,
both using potassium permanganate. The first involved adding the potassium permanganate to the samples (both dissolved in acid) in order to determine the total amount
of manganese present. The second titration involved first mixing the dissolved sample with ferrous ammonium sulfate in order to reduce nickel and manganese to the
2+ oxidation state while oxidizing some iron to 3+ state. The subsequent titration
with potassium permanganate then reduced iron back to 2+. The two measurements
allowed the determination of the average manganese oxidation state (assuming all
nickel was in the 2+ state). As such, a result for the manganese oxidation state
greater than 4.0 would imply some Ni
3+ was present. It is important to notice that
this method cannot distinguish between a Ni
2+ –Mn
4+ pair and a Ni
3+ –Mn
3+ pair,
since this approach essentially counts the number of oxidation states above 2+. To
make the distinction between these two combinations, manganese X-ray absorption
spectra were taken as described in the next section. The titrations were performed
by Oliver Schilling of Erachem Comilog.