Intrinsic lithium storage mechanisms and superior electrochemical behaviors of monodispersed hierarchical CoCO3 sub-microspheroids as a competitive anode towards Li-ion batteries

Recently, CoCO3 is attracting extensive interests as a promising anode for Li-ion batteries (LIBs) thanks to its large capacities and simple synthesis. However, its modest electrochemical behaviors and ambiguous lithium storage mechanisms still need to be well addressed. Herein, we devise a scalable bottom-up solvothermal methodology to fabricate monodispersed pinecone-like CoCO3 sub-microspheroids constructed with nanosheet subunits. When evaluated as appealing anode for LIBs, the resultant CoCO3 anode exhibits high initial Coulombic efficiency of ∼75.2%, and large reversible capacity of ∼1008 mAh g−1 at a rate of 200 mA g−1, and even ∼663 mAh g−1 at 2 A g−1, benefiting its hierarchical micro-/nanostructures. Besides, the enhanced interfacial charge-storage capability of the CoCO3 sub-microspheroids with cycling accounts for the long-duration capacity retention of ∼138% over 500 consecutive cycles. More significantly, comprehensive lithium storage mechanism of the CoCO3, involving conventional conversion reactions, reversible redox reaction of low-valence C/C(IV), and debut observation of reversible Co(II)/Co(III) transition, is proposed with in-situ and ex-situ physicochemical and electrochemical investigations. Furthermore, a CoCO3//LiNi0.8Co0.15Al0.05O2 full battery is assembled and delivers prominent electrochemical properties, hugely highlighting the enormous potential of our CoCO3 sub-microspheroids in next-generation LIBs as competitive anodes.