The Synthesis And Properties Of Na₃V₂?PO₄?₃/C And Li_xNa_3-xV₂?PO₄?₃/C Composite Materials

In this paper,Na₃V₂?PO₄?₃/C composites with different structures were synthesized by using sodium lignosulfonate,cellulose and 3,5-dinitrosalicylic acid as templates,which improved the electrochemical performance of the composites.The influence of the synthesis process,composition and structure on the properties were explored.On this basis,Li_xNa_3-xV₂?PO₄?₃/C composites were synthesized by lithium doping.The composition,structure,electrochemical performance of half-cell and full cell were studied,and the ion transport mechanism in lithium-sodium mixed ion battery was explored.The composite material of Na₃V₂?PO₄?₃/C was synthesized by solvothermal assisted method using cellulose as template and carbon source.The results show that the addition of cellulose provides growth points for Na₃V₂?PO₄?₃,avoiding the agglomeration of large particles,forming the morphology of Na₃V₂?PO₄?₃ coated cellulose carbon and increasing the electron conductivity.The solvothermal process ameliorates the interface and the stability of the material.The electrochemical performance of the composite is best when the amount of cellulose added is 1.5 g.At 50 C,the discharge specific capacity of 98 mAh g^-1 is still obtained.After 600 cycles,the specific discharge capacity is 85 mAh g^-1.In the full cell,it has a specific capacity of 85 mAh g^-1 at 2 C rate,and can still reach 57 mAh g^-1 after 300 cycles.In addition,a simple method of pre-sodiumation was explored.By adding a small amount of metal sodium foil,the sodium loss was compensated.Na₃V₂?PO₄?₃ ultrathin sheet/N-doping hard carbon ultrathin sheet was synthesized using sodium lignosulfonate as template.The results show that NaVP₂O₇ impurities can adversely affect the electrochemical performance of Na₃V₂?PO₄?₃.The appropriate excess of sodium component can inhibit the formation of NaVP₂O₇ impurities.The NHCUS acts as a conductive network for better electron conductivity.The NVPUS is uniformly deposited between the two NHCUS to form a stable sandwich sandwich structure,which effectively improves the transport of electrons and ions,alleviates the damage of the structure caused by volume change,and improves the rate performance and cycle stability.When V₂O₅/SLS/Na₂CO₃=2:1.5:1.7,the composite has excellent electrochemical performance(with a specific discharge capacity of 117.3 mA h g^-1 at 0.1 C rate,82 mAh g^-1 at 100 C).Even at 200 C,the discharge specific capacity is still reach 78 mAh g^-1,and after 6000 cycles the specific discharge capacity is 40 mAh g^-1.The Na₃V₂?PO₄?₃/C composites with different particle structures were synthesized by hydrothermal treatment using 3,5-dinitrosalicylic acid as template.The results show that the composite contains 3-6?m spherical particles,200-400 nm rhombohedral dodecahedral particles and some irregular particles when the amount of DNS is 3 mmol.This may be due to the difference in solubility of DNS in water and ethanol,resulting in a microreactor similar to microemulsion in the reaction system,which limits the growth of Na₃V₂?PO₄?₃ crystals.The microreactive droplets of different sizes result in the formation of spherical and rhombohedral dodecahedral particles of varying sizes.The composite material with this structure exhibites high rate performance,has a reversible discharge specific capacity of 73 mAh g^-1 at 100 C.The Li_xNa_3-xV₂?PO₄?₃/C composites were prepared by changing the ratio of sodium source and lithium source by using cellulose as the carbon source.The results show that Li_xNa_3-xV₂?PO₄?₃/C electrode materials have good compatibility.As a lithium ion battery,Li₂NaV₂?PO₄?₃/C exhibits a high specific capacity and excellent rate performance due to a structure inducing effect.The specific discharge capacitie is 138 mAh g^-1,128 mAh g^-1,117 mAh g^-1 and 98 mAh g^-1 at 0.5-20 C respectively.However,due to the structural changes of the polycrystalline phase is different during ion intercalation and deintercalation,the cycle performance is inferior to that of Li₃V₂?PO₄?₃/C.Na₃V₂?PO₄?₃/C has a significant polarization phenomenon as a cathode for lithium ion batteries due to the influence of Na?1?sodium ion on lithium ions.Studies on mixed electrolytes shows that lithium ions preferentially transport and participate in the reaction when lithium ions and sodium ions coexist.The addition of lithium ion reduces the insertion rate of sodium ions at the cathode,causing the polarization phenomenon to be aggravated and affecting the electrochemical performance.The battery design of the semi-metal sodium and lithium anode can realize the common transmission of sodium ions and lithium ions,and the specific capacity at 0.1 C is 111 mAh g^-1.