# 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-Based Alloys and Its Composites

Table 2: _Cont._As an inactive component of cobalt-based alloys, the presence of phase cobalt can alleviate the volume fluctuation as a protective matrix, thereby improving the electrochemical performances of cobalt-based alloys. Despite these features, the electrochemical properties of cobalt-based alloys are still disturbed by the pulverization and shedding of active materials during periodical cycles. Many cobalt-based alloys have been reported as anode materials for LIBs or SIBs with outstanding electrochemical properties owing to their unique structures and suitable compositions [40; 55; 67; 81; 83; 92; 104; 105; 171]. [PERSON] et al. reported a novel structure with a Sn-Co alloy embedded in porous N-doped carbon microboxes that exhibited a superior electrochemical performance when used as anode materials for LIBs [64]. In Figure 9a, the Sn-Co@C-2 electrode exhibited the highest specific capacity at various current densities, from 0.1 to 2 A g\({}^{-1}\), indicating a superior rate performance. Furthermore, the Sn-Co@C-2 electrode delivered outstanding capacity retention when the current density went back to 0.1 A g\({}^{-1}\). Ex-situ XRD of the Sn-Co@C-2 electrode before and after cycles are shown in Figure 9b. CoSn2 disappeared after the first cycle, and the CoSn phase maintained well even after 100 cycles, suggesting a good reversibility of the Sn-Co@C-2 electrode. Figure 9: Electrochemical performances of cobalt-based anode materials. (**a**) Rate performances of Co@C, Sn-Co@C-1 and Sn-Co@C-2 as anode materials of LIBs. (**b**) XRD patterns of the Sn-Co@C-2 electrode before and after the charge-discharge cycles [64]. (**c**) Cycle performance and (**d**) charge/discharge profiles of the SnCo@CNT-3 DC electrode at 50 mA g\({}^{-1}\) in the voltage range of 0.005–3 V vs. Li/Li\({}^{+}\)[44]. (**e**) Cycle performance of the Sn-Co-CNT@CNT nanostructure tested at 0.1 C (1C = 990 mA g\({}^{-1}\)). (**f**) TEM image of the Sn-Co-CNT@CNT anode materials after 200 cycles at 1C in LIBs [67]. He's group reported a novel method for the one-step synthesis of hierarchical SnCo@CNT-3 DC [44]. When used as anode materials for LIBs, this unique structure can provide numerous channels for electron transfer, shorten the diffusion pathway of Li\({}^{+}\) and ensure the permeation of electrolytes. As shown in Figure 9c, the SnCo@CNT-3 DC electrode displayed a high capacity of 826 mA h g\({}^{-1}\) after 100 cycles at 0.1 A g\({}^{-1}\). Compared with the first discharge capacity, the capacity retention rate is 113%. During the cycles, there is a slight increase in capacity owing to the increasing electrochemical reaction of the SnCo nanoparticles caused by the activation of the electrode materials. As for the SnCo/C electrode, the relatively low capacity of 429.6 mA h g\({}^{-1}\) was retained after 50 cycles at 0.1 A g\({}^{-1}\). These results can be probably ascribed to the better transformation of lithium in the SnCo@CNT-3 DC electrode. Figure 9d shows that the SnCo@CNT-3 DC electrode delivered a high discharge capacity of 1154.4 mA h g\({}^{-1}\), with an initial coulombic efficiency (CE) of 61%. As the number of cycle increases, the capacity decreases slightly, suggesting good capacity retention. [PERSON]'s group demonstrated an in-situ template technique for the preparation of the Sn-Co-CNT@CNT ternary tube-in-tube nanostructure [67]. When utilized as anode materials for LIBs, superior electrochemical properties were obtained owing to the confined volume change in the nanotube cavities and ensured a permanent electrical connectivity of the immobilized Sn-Co anodes. As shown in Figure 9e, the Sn-Co-CNT@CNT electrode with 45.4% Sn delivered a discharge capacity of 811 mA h g\({}^{-1}\) after 200 cycles, with 91.1% of the initial discharge capacity retained. The TEM image of the Sn-Co-CNT@CNT anode after 200 cycles demonstrates that the 1D nanotube-like structure was retained, indicating its structural stability during the cycles (Figure 9f).