**5. Electrochemical characterization results**

The respective LNMO doped active materials were coated on aluminum foils using different formulations of active material, carbon and binder – as explained below – in order to study the material ratios and process parameters for slurry preparation and battery performance optimization. The coated material was also tested under different calendering densities, by varying the calendering pressure and final active layer thickness. The coated electrodes were analyzed for their electrochemical performance in the form of Half Coin Cells (HCC) with a metallic Lithium foil as counter electrode and evaluating their discharge specific capacity. Preliminary electrochemical tests were performed on all four materials using HCCs (3 cells per formulation/material). Discharge C-rate varied from C/5 to 10C on comparable electrodes prepared with a formulation AM/Carbon/PVdF ratio of 90/5/5, a real loading ~1.5 mAh. cm−2 and density of 2.5 g. cm−3.

As depicted in **Figure 8**, a profound specific discharge capacity decay was observed in both pristine and Mg-doped LNMO during cycles 1 to 5 (C/5 low rate and near-zero values were recorded until cycle 32 at high C-rates. Al-doped LNMO demonstrated high specific capacity values (~120 mAh. g−1) at low C-rates i.e. C/5, C/2, 1C while at higher discharge C-rates of 2C, 5C, 8C and 10C the specific capacity demonstrated values of ~110, ~90, ~50 and ~ 20 mAh. g−1 respectively. The discharge specific capacity almost regained its initial high values when C-rate was decreased at C/2 during cycle 24 and withstood high charge rates (~80 mAh/g at 3C charge, cycles 29–31). On the other hand, Fe-doped LNMO demonstrated similar behavior during cycles 1–8, however the performance was clearly poorer than the Al-doped LNMO composition at 2C and 5C (i.e. ~90 and ~ 18 mAh. g−1 respectively) while it dropped to zero during fast discharge at 8C and 10C. During the C-rate

### **Figure 8.**

*Specific capacity of the different doped LNMO electrodes at different discharge rates (1C to 10C) and charge rates (1C, 3C).*

**Figure 9.**

*Specific capacities of iron and aluminum doped LNMO for the same target loading of ~1.0 mAh. cm−2 under different electrode formulations and densities (a) 80/10/10\_D1.5, (b) 84/8/8\_D1.5 and (c) 84/8/8\_D1.8 (D in g. cm−3).*

reduction at cycle 24 (C/2), an increase in specific discharge capacity to the initial values was observed but again performance was inferior to the Al-doped LNMO case throughout cycles 25–32.

*Aerosol Spray Pyrolysis Synthesis of Doped LiNi0.5Mn1.5O4 Cathode Materials… DOI: http://dx.doi.org/10.5772/intechopen.100406*

Based on the abovementioned electrochemical results, Fe-doped and Al-doped LNMO were chosen for further testing in HCCs in order to study the effect of the AM/Carbon/PVdF and electrode density on the electrochemical performance.

The effect of electrode formulations with higher conducting carbon content to improve electrical conductivity and the calendering density on electrochemical performance of Fe-doped and Al-doped LNMO is depicted in **Figure 9(a)–(c)**. The materials were tested with high C black content, an AM/carbon/PVdF ratio 80/10/10 ratio, that limited the achievable loading to 1 mAh. cm−2 and a density of 1.5 g. cm−3. **Figure 9(a)** depicts low C-rates of C/5 to 1C during cycles 1–8; Fe-doped LNMO demonstrated higher values of specific discharge capacity compared to Al-doped LNMO (~138 and 118 mAh. g−1 respectively), while similar performance in the range 80–100 mAh. g−1 was observed in the higher C-rate of 5C (cycles 13–15). Increasing the amount of active material to optimize the energy density of the active layer while maintaining slurry stability, achieved an AM/carbon/PVdF ratio of 84/8/8. As shown in **Figure 9(b)**, the Al-doped LNMO performance demonstrates a capacity improvement while a capacity reduction is observed in the case of Fe-doped LNMO. During cycles 1–4 (C/5 and C/2 rates) the specific capacity reaches values ~137 and 125 mAh. g−1 for Al-doped and Fe-doped LNMO respectively, with further decrease at 1C rate (130 and 120 mAh. g−1 respectively) and 2C rate (105 and 95 mAh. g−1 respectively). Both materials demonstrate zero capacity at 5C rate. On subsequent charge at 1C during cycles 17–19, a decrease in Al-doped LNMO capacity is observed compared to 1C discharge cycles 5–7 while insignificant change in Fe-doped LNMO was observed in the course of the same cycles. During 3C charge (cycles 21–23), Fe-doped LNMO performed better than Al-doped LNMO with a specific capacity of ~95 vs. 85 mAh. g−1 for the Al-doped LNMO composition.

Finally, by further increase of the density to 1.8 g. cm−3, a significant improvement of Al-doped LNMO performance was observed, especially at the higher C-rates of 2C, 3C and 5C in **Figure 9(c)**. On the contrary, no improvement was observed in the case of Fe-doped LNMO, as the capacity values remained almost the same as for 1.5 g. cm−3 densification. The enhanced electrochemical activity of the Al-doped LNMO at the 1.8 g. cm−3 density comparing to that of 1.5 g. cm−3 shows the importance of the physicochemical properties of the overall electrode, beginning from the nanoscale of Al ion doping in the LNMO lattice to the macroscale attributed to the density of the coated electrode; the conductivity (Li-ion mobility and electrical conductivity) of the cathode increases when carbon and LNMO particle interfaces are in better contact by calendaring.
