Mixed structures as a new strategy to develop outstanding oxides-based cathode materials for sodium ion batteries: A review

Sodium ion batteries(SIBs)are an exciting alternative for post-lithium energy storage.They can be regarded as a promising and cost-efficient solution for grid applications as they exhibit similar’rocking chair’mechanism as lithium ion batteries,in addition to the abundance and low cost of sodium resources.Indeed,electrode materials,electrolytes,separators and smart design strategies are under spot and researchers are competing to come up with the ideal battery.Layered oxides with mixed structures are regarded as new concept that can offer a set of desired structural and energetic properties and are an attractive choice for next generation sodium ion batteries.However,unlocking this system chemistry,kinetics and reliable understanding of the intercalation/deintercalation mechanism upon electrochemical cycling is quite challenging.This review,through the examination of literature,gives a brief summary of the research progress and recent advances in the investigation of electrode materials based on layered oxides with mixed structures for sodium ion batteries.This new strategy leads in fact to positive electrodes with enhanced energetic performance as they consist of a combination of the energetic or/and structural properties of the existing structures.

Elucidation of the sodiation/desodiation mechanism in Ca_(0.5)Ti_(2)(PO_(4))_(3)/C as promising electrode for sodium batteries: New insights into the phase transitions

The structure evolution and electrochemical performance of Na SICON-type Ca_(0.5)Ti_(2)(PO_(4))_(3) for sodium batteries are presented.This phosphate was synthesized by a solid-state method,and the obtained particles were coated with carbon using sucrose.This compound crystallizes in the rhombohedral system with space group R-3.The presence of carbon in the Ca_(0.5)Ti_(2)(PO_(4))_(3)/C composite was confirmed by Raman and Thermogravimetric analysis.The electrochemical performance of Ca_(0.5)Ti_(2)(PO_(4))_(3)/C was investigated in the potential window 1.5–3.0 V vs.sodium metal at different scan rates.The compound is able to initially intercalate/deintercalate 1.6/1.15 Na per formula unit,respectively.In operando synchrotron diffraction was done in the potential window 0.02–3.0 V vs.Na|Na+and revealed the occurrence of several reaction regions upon first discharge.Up to 4 Na+ion per formula unit can be inserted during the first discharge.An intensive refinement of the synchrotron X-ray diffraction(SXRD)patterns of discharged Ca_(0.5)Ti_(2)(PO_(4))_(3) evidenced the existence of five regions depending on the sodium content while the crystal structures of new phases were elucidated for the first time where sodium insertion occurs in the unusual M3 and M’3 sites of the Na SICON structure.