# The Progress of Cobalt-Based Anode Materials for Lithium Ion Batteries and Sodium Ion Batteries
## 4 Application of Cobalt-Based Anode Materials in LIBs/SIBs
### Cobalt Oxides and Its Composites  
Cobalt oxides have been identified as hopeful anode materials for LIBs and SIBs due to their high theoretical capacities, natural abundances, and low costs. For instance, Co\({}_{3}\)O\({}_{4}\), as the most common cobalt oxide, has a theoretical capacity of 890 mA h g\({}^{-1}\) attributed to its eight-electron transfer reaction during cycling. However, the intrinsic defects of cobalt oxides, including low structural stability and poor electrical conductivity, lead to inferior electrochemical properties [57; 63; 77; 78; 111; 113; 116; 118; 120]. [PERSON]'s group reported hierarchically structured Co\({}_{3}\)O\({}_{4}\)@ carbon porous fibers to circumvent the volume fluctuation issue during lithiation/delithiation [11]. As shown in Figure 10a, the initial discharge and charge specific capacity of ES-CNCo\({}_{3}\)O\({}_{4}\) was 1824 and 1003 mA h g\({}^{-1}\), with an initial columbic efficiency of 55%. After five cycles, the charge/discharge profiles were almost overlapped, indicating the high stability of the composite. [PERSON] et al. synthesized yolk-shell Co\({}_{3}\)O\({}_{4}\)/C dodecahedrons to solve the problem of volume change during lithiation or sedation [129]. When utilized as an anode for LIBs, the yolk-shell Co\({}_{3}\)O\({}_{4}\)/C electrode delivered a high discharge capacity of 1100 mA h g\({}^{-1}\) after 120 cycles. Regarding Co\({}_{3}\)O\({}_{4}\)-B, a lower specific capacity of 400 mA h g\({}^{-1}\) after 50 cycles was obtained, suggesting a better lithium storage performance of yolk-shell Co\({}_{3}\)O\({}_{4}\)/C. Figure 10c shows the sodium storage performance of yolk-shell Co\({}_{3}\)O\({}_{4}\)/C at a current density of 1 A g\({}^{-1}\). The second discharge capacity of the sample was 395 mA h g\({}^{-1}\), and the specific capacity of 240 mA h g\({}^{-1}\) was obtained after 200 cycles, suggesting the great electrochemical properties of yolk-shell Co\({}_{3}\)O\({}_{4}\)/C in SIBs. [PERSON]'s group reported a porous starfish-like nanocomposite of N-doped carbon with Co\({}_{3}\)O\({}_{4}\) coating [128]. The Co\({}_{3}\)O\({}_{4}\)@N-C electrode as a LIB anode delivered an initial specific capacity of 1235 mA h g\({}^{-1}\) and a capacity of 795 mA h g\({}^{-1}\) after 300 cycles, indicating a superior lithium storage performance to pure Co\({}_{3}\)O\({}_{4}\) (Figure 10d). To better understand the gap between the electrochemical performances of the two samples, Nyquist plots of Co\({}_{3}\)O\({}_{4}\)@N-C and pure Co\({}_{3}\)O\({}_{4}\) electrodes were fitted (Figure 10e). It is clear that the Co\({}_{3}\)O\({}_{4}\)@N-C composite exhibited smaller charge-transfer resistance, suggesting that the porous structure accelerates the diffusion of Li\({}^{+}\), and the presence of N-doped carbon improves the electrical conductivity of the sample, finally resulting in the superior electrochemical properties of Co\({}_{3}\)O\({}_{4}\)@N-C. [PERSON]'s group reported the preparation of a Ni-doped Co/CoO/N-doped carbon hybrid, with Ni-Co-ZIF as the precursor [126]. When utilized as an anode material for SIBs, the Ni-doped Co/CoO/NC electrode exhibited a high discharge capacity of 218.7 mA h g\({}^{-1}\) after 100 cycles, with 87.5% capacity retained (Figure 10f). Figure 10: Electrochemical performances of cobalt-based anode materials. (**a**) Galvanostatic discharge-charge profiles of ES-CNCo\({}_{3}\)O\({}_{4}\) at 0.1 A g\({}^{-1}\)[11]. (**b**) Cycling performance of the yolk-shell Co\({}_{3}\)O\({}_{4}\) and Co\({}_{3}\)O\({}_{4}\)-B at 0.2 A g\({}^{-1}\) for LIBs. (**c**) Cycling properties of the yolk-shell Co\({}_{3}\)O\({}_{4}\) at 1 A g\({}^{-1}\) for SIBs [129]. (**d**) Cycling performance of Co\({}_{3}\)O\({}_{4}\) and Co\({}_{3}\)O\({}_{4}\)@N-C at 0.5 A g\({}^{-1}\). (**e**) Electrochemical impedance spectra for Co\({}_{3}\)O\({}_{4}\) and Co\({}_{3}\)O\({}_{4}\)@N-C [128]. (**f**) Cycling performance of the Ni-doped Co/CoO/NC electrode and the corresponding columbic efficiencies at 0.5 A g\({}^{-1}\)[126].