**2.3. Material characterization**

The structure of the materials generated in this work were identified by X-ray diffraction using a Phillips 1710 diffractometer equipped with a Cu Kα radiation source (λ=1.5418 Å) and operated at 40 kV and 30 mA. The scan range was from 10° to 80° 2θ, with a step size of 0.05° and a count time of 2.5 s. Analysis of the diffraction patterns was carried out by fitting a Lorentzian lineshape to individual peaks, with the fitting parameters then used to calculate structural properties such as the fraction of pyrolusite (Pr; as described by Chabre and Pannetier [9]) and the unit cell parameters.

Morphology was examined by gas adsorption using a Micromeritics ASAP 2020 Surface Area and Porosity Analyser. A representative 0.10 g sample of the manganese dioxide material was degassed under vacuum at 110°C for 2 h prior to analysis. An adsorption isotherm was then determined over the partial pressure (P/P0) range of 10-7-1 using N2 gas as the adsorbate at 77 K. The specific surface area was extracted from the gas adsorption data using the linearized BET isotherm [10] in the range 0.05<P/P0<0.30, while the pore size distribution was determined using a Density Functional Theory-based approach (Micromeritics DFTPlus V2.00).

The composition of the materials was determined using two consecutive potentiometic titrations (Pt indicator and SCE reference electrode) as outlined in Vogel [11]. A blank titration was carried out first in which 10 mL of acidified 0.25 M ferrous ammonium sulfate (NH4FeSO4.6H2O, BDH Chemicals, 99%) was titrated with a standardised 0.03 M potassium permanganate solution (KMnO4, Ajax Finechem, 99%; standardized using the oxalate method [11]), and the volume of permanganate added to reach the end point denoted as V0. Sample analysis was conducted by digesting 0.050 g of the manganese dioxide being studied into another 10 mL aliquot of the acidified 0.25 M ferrous ammonium sulfate solution. After complete dissolution the resultant solution was then titrated using the same 0.03 M permanganate solution, with the volume to reach the end point recorded as V1. For this

#### 274 Heat Treatment – Conventional and Novel Applications

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 x in MnOx was then calculated using:

$$\infty \le 1 + \frac{5(\mathbf{V}\_0 \cdot \mathbf{V}\_1)}{2(4\mathbf{V}\_2 \cdot \mathbf{V}\_1)} \tag{4}$$

Monitoring the Effects of Thermal

Treatment on Properties and Performance During Battery Material Synthesis 275

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

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

The electrochemical characteristics of the cells prepared were assessed using a Perkin-Elmer VMP multichannel potentiostat/galvanostat on which a modular galvanostatic discharge

The compositional, morphological and structural data for the starting EMD sample are shown in the first row of Table 1. While the details of these initial properties and the resulting changes to the measured parameters as a result of heat treatment will be discussed in detail later, we note here that the EMD chosen for this work is a typical EMD sample. The composition of samples prepared via electrolysis can vary considerably depending on the experimental deposition conditions. We find that the compositional data collected for our starting EMD fit comfortably within the typical range for samples termed EMD [12]. The structure of the starting EMD, as measured by XRD, is shown in Figure 1. The Miller indicies for the peaks in the starting EMD pattern are labelled assuming an orthorhombic

**Composition**

**(%) CVF %H2O** 

**(>110°C)** 

**%H2O (<110°C)** 

**Mn(III)** 

25 59.45 55.34 4.11 0.081 2.13 4.11 200 59.00 55.03 3.98 0.051 1.67 2.73 250 61.47 57.28 4.20 0.027 1.60 1.81 300 61.82 55.22 6.60 0.008 1.66 1.41 350 60.94 54.94 6.00 0.000 0.94 0.84 400 60.41 53.79 6.61 0.000 1.15 0.90

introduction into an Ar-filled dry box, where cell construction took place.

equilibrate for 3-4 days before being used for electrochemical testing.

program was performed at rates of 2, 5, 10 and 20 mA/g of active material.

**2.5. Electrochemical performance** 

**3. Data analysis** 

unit cell.

**Temp (oC)** 

**3.1. Starting material properties** 

**Mn(T) (%)** 

**Mn(IV) (%)** 

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 using:

$$\% \text{Mtr} = \frac{n\_{\text{Mn}}}{n\_{\text{MnO}\_2(4\eta)}} \times 100\tag{5}$$

To calculate the relative proportion of manganese (III) and (IV) species (%Mn(III) and %Mn(IV) respectively), we have:

$$\% \text{Mrn(III)=(4-2x)\*\%Mn} \tag{6}$$

$$\% \text{Mn} (\text{IV}) \text{\*} (\text{2x-3}) \text{\*} \% \text{Mn} \tag{7}$$

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 400°C for 2 h, and using:

$$\text{CVF} \stackrel{\text{m}}{=} \begin{array}{c} \text{m} \\ \text{m} \end{array} \tag{8}$$

where

$$\mathbf{m} = (\mathbf{2} \cdot \mathbf{x}) \mathbf{+} \frac{\mathbf{M}\_{\mathbf{M} \cap \mathbf{x}} \times \mathbf{H} \mathbf{z} \mathbf{O} (\mathbf{x} \cdot \mathbf{1} \mathbf{1} \mathbf{0}^{\circ} \mathbf{C})}{\mathbf{M}\_{\mathbf{H} \mathbf{z} \mathbf{O}} \mathbf{x}^{\circ} \mathbf{M} \mathbf{m}} \tag{9}$$

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

#### **2.4. Thermal treatment of EMD**

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 cool to room temperature.
