# The Progress of Cobalt-Based Anode Materials for Lithium Ion Batteries and Sodium Ion Batteries
###### Abstract  
Limited by the development of energy storage technology, the utilization ratio of renewable energy is still at a low level. Lithium/sodium ion batteries (LIBs/SIBs) with high-performance electrochemical performances, such as large-scale energy storage, low costs and high security, are expected to improve the above situation. Currently, developing anode materials with better electrochemical performances is the main obstacle to the development of LIBs/SIBs. Recently, a variety of studies have focused on cobalt-based anode materials applied for LIBs/SIBs, owing to their high theoretical specific capacity. This review systematically summarizes the recent status of cobalt-based anode materials in LIBs/SIBs, including Li\({}^{+}\)/Na\({}^{+}\) storage mechanisms, preparation methods, applications and strategies to improve the electrochemical performance of cobalt-based anode materials. Furthermore, the current challenges and prospects are also discussed in this review. Benefitting from these results, cobalt-based materials can be the next-generation anode for LIBs/SIBs. cobalt-based materials; anode; lithium ion battery; sodium ion battery +
Footnote †: journal: Applied Physics Letters  
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Footnote 1: School of Energy and Power Engineering, North University of China, Taiyuan 030051, China 1  
Up to now, unceasing efforts have been devoted to exploring appropriate anode materials, like metal chalcogenides, alloying metals, metal phosphide and carbon materials. Among these materials, cobalt-based composites (oxides, sulfides, phosphides and alloys) have recently drawn enormous attention owing to their outstanding electrochemical performances. For example, [PERSON] et al. synthesized a porous fiber structured Co\({}_{3}\)O\({}_{4}\)@carbon for LIBs that delivered a capacity of 558 mA h g\({}^{-1}\) after 500 cycles at a current density of 5 A g\({}^{-1}\)[11]. [PERSON]'s group fabricated a spongy CoS\({}_{2}\)/carbon composite that showed marvelous electrochemical performances as anode materials for both LIBs and SIBs. It retained a capacity of 610 mA h g\({}^{-1}\) after 120 cycles at 0.5 A g\({}^{-1}\) in LIBs and 330 mA h g\({}^{-1}\) after 60 cycles at 0.5 A g\({}^{-1}\) in SIBs, respectively [12]. [PERSON] and his colleagues synthesized CoP nanoparticles embedded in N-doped carbon nanosheets that displayed a Na-storage capacity of 598 mA h g\({}^{-1}\) at 0.1 A g\({}^{-1}\)[13]. Nonetheless, a large proportion of cobalt-based electrode materials are subjected to severe volume fluctuations caused by the uptaking and releasing of Li\({}^{+}\) or Na\({}^{+}\), which eventually yield a pulverization of electrode materials and detachment from the current collector, finally giving rise to a decaying of capacity [14; 15; 16]. To circumvent these issues, plenty of cobalt-based materials with special structures have been reported [17; 18; 19; 20]. In general, active materials with a nanometer scale can be conducive to the transfer of Li\({}^{+}\) or Na\({}^{+}\) owing to shorter diffusion lengths and tolerate the strain caused by volume expansion during periodical cycle processes, consequently enhancing electrochemical performances [21; 22]. [PERSON] et al. fabricated Co\({}_{9}\)S\({}_{8}\)@carbon nanospheres with an average size of 60 nm, which delivers an astonishing rate capability of 305 mA h g\({}^{-1}\) after 1000 cycles at 5 A g\({}^{-1}\) for anode materials of SIBs [23]. CoSe\({}_{2}\)/N-doped carbon nanofibers synthesized by [PERSON]'s group shows excellent structure retention. Even cycled for 1000 cycles, the sample well maintained its original structure without pulverization or amorphization [24]. Furthermore, the electrochemical properties of cobalt-based materials can also be improved by combining with carbonaceous buffers [19; 25; 26]. Beneficially, the carbonaceous buffer can enhance the electrical conductivity of the composite, as well as mitigate pulverization and aggregation during periodical cycles. [PERSON] et al.