# 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 Phosphide and Its Composites  
Cobalt phosphides, as promising electrode materials, have been studied as anode materials for LIBs/SIBs. Compared with cobalt oxides and sulfides, cobalt phosphides possess higher gravimetric/volumetric specific capacities. The main drawbacks that restrict their applications are the severe volume expansion during lithiation or sedation and poor electrical conductivities. Many efforts have been made to circumvent these issues [18; 31; 46; 82; 134; 136; 137; 188; 189]. [PERSON]'s group hybridized the Co\({}_{2}\)P nanoparticles with N-doped carbon matrices and tested the composite as an anode material for SIBs [143]. Except for the initial discharge profile, the profiles of the galvanostatic charge-discharge process overlapped well with each other, indicating a good reversibility of Co\({}_{2}\)P@N-C@rGO (Figure 12a). [PERSON]'s group successfully fabricated Co\({}_{x}\)P nanostructures with controlled phases, sizes and shapes. When applied as the anode material of LIBs, the hollow CoP particles delivered a capacity of 630 mA h g\({}^{-1}\) after 100 cycles, as shown in Figure 12b. With regard to solid CoP nanoparticles, a capacity of 480 mA h g\({}^{-1}\) was retained after 100 cycles. Better cycling performance of the hollow CoP electrode can be ascribed to the hollow structure, which ensures effective lithiation/delithiation and alleviates the volume change during periodical cycling. Figure 11: Electrochemical performances of cobalt-based anode materials. (**a**) Cycle performance of CoS\({}_{2}\)-quantum-dots-anchored graphene nanosheets (CoS\({}_{2}\) NP@C-CoS\({}_{2}\) QD) at 1 A g\({}^{-1}\). (**b**) Nyquist plots of CoS\({}_{2}\) and CoS\({}_{2}\) NP@C-CoS\({}_{2}\) QD electrodes after 300 cycles [187]. (**c**) Ex-situ XRD of the cobalt sulfides quantum dots@mesoporous hollow carbon polyhedral@reduced graphene oxide (CoS\({}_{8}\) QD@HCP)@rGO electrode tested at different voltage states [172]. (**d**) Schematic illustration and (**e**) cycle performance of CoS@rGO/Na\({}_{3}\)VPO\({}_{4}\) (NVP)@C sodium ion full cell [173]. (**f**) Rate performance of CoS\({}_{2}\) bubble-like hollow prisms [174]. (**g**) Cycle performance of Co\({}_{9}\)S\({}_{6}\)-650@C in LIBs [175]. (**h**) Cycle performance of Multiwalled carbon nanotube@a-C@Co\({}_{9}\)S\({}_{8}\) nanocomposites (MWCNT@a-C@Co\({}_{9}\)S\({}_{8}\)) anode for LIBs [5]. [PERSON]'s group firstly synthesized a novel composite with core-like CoP embedded in N, P co-doped porous carbon sheets (CoP\(\subset\)NPPCS) [141]. When utilized as an anode material of LIBs, the CoP\(\subset\)NPPCS electrode delivered reversible capacities of about 709, 500, 501, 410 and 357 mA h g\({}^{-1}\) at the current densities of 0.1, 0.2, 0.5 and 1.0 A g\({}^{-1}\), respectively. It is worth noting that the capacity retention was over 50% when the current density was expanded by 20 times, indicating the excellent rate capability. [PERSON]'s group prepared Co\({}_{2}\)P-Co (Co-P) hollow nanospheres decorated with graphene sheets and tested them as anode materials for LIBs [139]. When the current densities increased from 0.2 C, 0.4 C, 0.6 C, 0.8 C and 1.0 C to 2.0 C (1C = 540 mA g\({}^{-1}\)), the capacity of Co-P/graphene correspondingly decreased from 855, 674, 628, 608 and 610 to 567 mA h g\({}^{-1}\). When the current density returned to 0.2 C, a high capacity of 1039 mA h g\({}^{-1}\) was retained even after 100 cycles (Figure 12d). Clearly, the rate performance of Co-P/graphene was better than their Co\({}_{2}\)P-Co counterparts, attributed to the presence of graphene, which improved the electrical conductivity of the electrode (Figure 12e). [PERSON] and co-workers synthesized a composite with cobalt phosphide nanowires and reduced the graphene oxide (CoP/RGO) [135]. As shown in Figure 12f, the cycle performances of CoP and CoP/RGO as anode materials of LIBs were displayed. The CoP/RGO electrode exhibited a higher capacity of 967 mA h g\({}^{-1}\) after 200 cycles.