**2.5. Electrochemical performance**

274 Heat Treatment – Conventional and Novel Applications

x in MnOx was then calculated using:

using:

where

x=1+ 5(V0-V1)

%Mn= nMn

CVF= <sup>m</sup>

m=(2-x)+ MMn×%H2O(>110°C)

and MMn and MH2O are the molar masses of manganese and water, respectively.

Approximately 10 g of EMD was heated in an alumina boat crucible by a Eurotherm HTC1400 furnace with a static air atmosphere set at the required temperature. After the elapsed isothermal heating time, the sample was removed from the oven and allowed to

%Mn(IV) respectively), we have:

400°C for 2 h, and using:

**2.4. Thermal treatment of EMD** 

cool to room temperature.

titration it is important to stop at or just after the end point has been attained. To the solution resulting from the first titration ~6 g of tetra-sodium pyrophosphate (Na4P2O7.10H2O, Ajax Finechem, 99%) was added and allowed to dissolve. The pH of this solution was then adjusted to lie within the range 6-7 by the drop-wise addition of ~0.20 M sulfuric acid. The second potentiometic titration was performed using the same 0.03 M permanganate solution, and the volume to reach the end point recorded as V2. The value for

2(4V2-V1)

The total manganese content in the sample can be found from the second titration by taking into account the amount of manganese added through the addition of permanganate in the first titration. Using this result, and the dry mass of the manganese dioxide sample, found by subtracting the mass of surface water lost from the sample after heating at 110°C (%H2O(<110°C)) from the original mass, the total manganese content (%Mn) can be found

nMnO2�dry�

To calculate the relative proportion of manganese (III) and (IV) species (%Mn(III) and

%Mn(III)=(4-2x)×%Mn (6)

 %Mn(IV)=(2x-3)×%Mn (7) Finally, the cation vacancy fraction (CVF) can be found by taking into account the percentage structural water (i.e., water removed after heating at 400°C, but above 110°C, (%H2O(>110°C)), found by considering the difference in mass after heating the sample at

(4)

×100 (5)

m+2 (8)

MH2O×%Mn (9)

To evaluate the electrochemical performance the heat treated materials prepared were first thoroughly mixed with graphite and polyvinylidene fluoride, in a 1:8:1 ratio. Around 0.30 g of this mixture was compressed in a 10 mm die press under 1 t into a disk electrode ~1 mm thick. The electrodes were dried at 110°C under vacuum and accurately weighed prior to introduction into an Ar-filled dry box, where cell construction took place.

CR2032 size coin cells were constructed for electrochemical testing. The coin cells were comprised of a heat treated EMD (HEMD) cathode, lithium metal anode, with electrolyte made up from 1 M LiPF6 (Sigma-Aldrich (≥99.99%) in 1:1 w/w of ethylene carbonate (EC, Sigma-Aldrich 99%) and dimethyl carbonate (DMC, Sigma-Aldrich 99+%). A Celgard 2400 micro-porous separator was used in these cells. After construction, cells were left to equilibrate for 3-4 days before being used for electrochemical testing.

The electrochemical characteristics of the cells prepared were assessed using a Perkin-Elmer VMP multichannel potentiostat/galvanostat on which a modular galvanostatic discharge program was performed at rates of 2, 5, 10 and 20 mA/g of active material.
