Among all components in battery, cathode material is one of the most crucial parts, for cathode material contributes a lot to a battery’s good performance. Sodium-ion batteries (SIBs) have attracted more and more attention for large-scale electrical energy storage due to the abundance and wide distribution of Na resources. Recently, researchers focus on layered transition metal oxide, for its stable structure. NaCrO₂ is one of the most promising sodium layered transition metal oxides as cathode material in SIBs, because of its excellent thermal stability and compatibility with non-aqueous electrolyte. Furthermore, certain remarkable advantages of NaCrO₂ have been reported, including a high theoretical capacity of about 250 mAh g^-1, although its practical reversible capacity is approximately 100 mAh g^-1.

Hard-carbon are considered as one of the most promising anode materials for sodium-ion batteries (SIBs), but there are still two main disadvantages of high cost and low initial coulombic efficiency to be overcomed for practical SIBs.

Herein, we report preparation of layered NaCrO₂ as sodium-ion battery cathode material using a gel-combustion method and a cheap pinecone derived biomass-bassed hard carbon (PHC) using a simple carbonization method as anode material for SIBs.

The electrochemical performance of layered NaCrO₂ is greatly affected by the calcination temperature due to difference microstructure and carbon content. The NaCrO₂ calcined at 850℃ shows the best electrochemical performance with a reversible capacity of 90 mAh g^-1 at a current density of 20 mA g^-1, along with a high initial coulombic efficiency and good cycling performance. To further study the microstructure of NaCrO₂, XRD and FESEM are used to study the structure and morphology of NaCrO₂.

The performance of PHC is greatly affected by the carbonization temperature due to different microstructure and impurity. The PHC carbonized at 1400℃ shows the best electrochemical performance with a reversible capacity of 345 mAh g^-1 at a current density 30 mA g^-1, along with a high initial coulombic efficiency of 85.4% and good cycling performance. To further study the microstructure of PHC, the amorphous structure is demonstrated by X-ray diffraction (XRD), Raman spectroscopy as well as high-resolution transmission electron microscopy (HRTEM).

We make a full cell using NaCrO₂ as cathode material and PHC1400 as anode material. The initial coulombic efficiency is 93%. The initial charge specific capacity based on anode material is 311 mAh g^-1, and the initial discharge specific capacity was 289 mAh g^-1 at a current density 30 mA g^-1. The specific capacity based on anode is 150 mAh g^-1 after 200 cycles. The full cell shows excellent electrochemical performance benefited by well-prepared cathode and anode materials.