## 2 Electrodes and Electrolytes for Lithium-Based Batteries
### Electrodes
#### 2.1.2 Cathodes
[150] reported the synthesis of porous LNVO powder using solution combustion. Similar to LMO, LiNi\({}_{1-\text{x-y}}\)Mn\({}_{\text{x}}\)Co\({}_{\text{y}}\)O\({}_{2}\) (NMC) type cathodes are widely seen as alternatives to LCO. The first study of these cathode types reported by Ohzuku et al. [152] with stoichiometry LiNi\({}_{1/3}\)Mn\({}_{1/3}\)Co\({}_{1/3}\)O\({}_{2}\) (NMC-333) exhibited good rate capability and practical capacity about 160 mAh/g. In alloys that maintain an equimolar ratio between Ni and Mn, only Ni and Co are electroactive, with Mn generally serving as a structural stabilizer [153; 154]. Xu et al. [155] reviewed several nickel rich cathode phases with reduced cobalt content. Across 35 unique NMC stoichiometries from 47 different literature reports, the mean cutoff voltage range is 2.7-4.4 V vs. Li/Li\({}^{+}\) with an average first cycle discharge capacity of 173 mAh/g. At higher operating voltages (3.0-4.5 V vs. Li/Li\({}^{+}\)), Jung et al. [156] reported the degradation of rhombohedral NMC-523 to be covered in a spinel phase Ni\({}_{0.45}\)Mn\({}_{0.2}\)Co\({}_{0.3}\) with spots of cubic NiO. The electrochemically inactive NiO rocksalt phase is shown to cover the NMC particles entirely when operating at 3.0-4.8 V. Most recent work to maintain the surface integrity of NMC particles has been focused on surface modification/doping [157], regulation of crystallinity [158; 159] and addition of electrolyte additives [160; 161; 162; 163]. Lv et al. [164] reported the doping of a nickel rich LiNi\({}_{0.83}\)Co\({}_{0.12}\)Mn\({}_{0.05}\)O\({}_{2}\) phase by co-precipitation and sintering with Mg. The sample sintered at 770 \({}^{\circ}\)C demonstrated an initial discharge capacity of 201.8 mAh/g, with 74% capacity retention after 200 cycles. Wu et al. [165] reported NMC-811 doped with Ga\({}^{3+}\) (Figure 5) to partially replace Mn\({}^{4+}\) by co-precipitation, demonstrating that the Ga\({}^{3+}\) doping contributed to the reduced polarization, lowered charge transfer resistance and increased diffusion coefficient. They observed that the best initial discharge capacity was lower than the undoped samples, but all doped samples showed much better capacity retention (-90%) after 100 cycles. Figure 4: Crystal structure of LiMVO\({}_{4}\) (M = Ni or Co). Reprinted from ref. [151] with permission of The Royal Society of Chemistry. Zhang et al. [166] reported doped NMC-811 with Ti using a solid-state synthesis method, demonstrating high initial discharge capacity (214.9 mAh/g at 0.1 C and 165.02 mAh/g at 1 C, 136.9 mAh/g at 5 C) and improved cyclic stability (77.01% after 150 th at 1 C and 86.54% after 50 th at 5 C) by increasing the interlayer spacing. They also reported a lithium diffusion coefficient of \(6.8\times 10^{-12}\) cm\({}^{2}\)/s. Fluorine doping has also been used to achieve better performance with NMC cathode material. Calcination with LiF was shown to increase the initial discharge capacity of NMC-811 to 213.5 mAh/g with an 87.7% capacity retention after 50 cycles at 1 C [167]. Better retention was obtained after ball milling and annealing the fluoride-doped particles. After annealing, the initial discharge capacity slightly decreased (200.8 mAh/g), but the capacity retention was greatly improved (95.7% after 50 cycles at 1 C). Wang et al. [168] used the co-doping of La and F to improve surface stability. In this study, the capacity retention was 86.63% and 80.79% after 200 cycles and 300 cycles at 1 C and 8 C, respectively, with an initial discharge capacity of 205 mAh/g at 0.1 C. The highest discharge capacity was achieved by doping NMC with tungsten. Zhang et al. [169] report an initial high discharge capacity of 259.2 mAh/g for W-doped Li\({}_{1.2}\)Mn\({}_{0.54}\)Ni\({}_{0.13}\)Co\({}_{0.13}\)O\({}_{2}\) through a sol-gel method. The valence state of tungsten was determined to be 6, and the resulting structure was identified as hexagonal \(\alpha\)-NaFeO\({}_{2}\). Hashigami et al.