Study On Sodium Or Lithium Ion Intercalation Active Cathode Materials With High-potential

The environmental problems should be payed more attention with the fast development of economy,and the environmental problems also lead to the development of new energy.The progress of new energy needs a new type of energy storage technology to support.The lithium-ion battery is the most mainstream energy storage method in our country,but there are still some pain points,such as lower voltage,more complex internal structure,shorter service life and higher cost of the battery materials and so on.These problems lead to higher cost of lithium-ion battery for energy storage.The study on the development and research of lithium or sodium intercalation materials with high potential is the main line in this paper.The prelithiation?presodiation?technology,low cost synthesis technology of cathode materials for sodium ion batteries which is useful to improve the cyclic life and reduce the cost of batteries is the auxiliary lines.The basic reference for a new type low cost energy storage system are provided in this paper by the optimization of high-potential lithium or sodium ion embedded cathode materials and the research on the materials'own full cells.In this work,it firstly introduces the synthesis of C-Li₂Fe_0.95Ni_0.05P₂O₇ by ethanol sol gel method.The material particles have submicron size?100-200 nm?and the particle surfaces are covered with a 2 nm thick carbon layer.The electrochemical test results have shown that:The sample of C-Li₂FeP₂O₇ and C-Li₂Fe_0.95Ni_0.05P₂O₇ can deliver the specific capacities of 96 mAh/g and 103 mAh/g at the rate of 0.1 C.The capacity retention is 61.4%and 92.5%after 100 cycles.The simulated full cell is assembled by the C-Li₂Fe_0.95Ni_0.05P₂O₇ cathode and graphite anode.The capacity retention of the full cell which has been prelithiated increases by 11.3%compared with that of none prelithiation cell.In this work,it also introduces the preparation and modification of LiMnPO₄ by Polyhydroxysolvothermalmethod.Thesecondaryparticlesofacquired C-LiMn_xFe_1-x-x PO₄ samples are spherical or annular,and the primary particles are nano-sized?20-80 nm?.The TEM image shows that the primary particles of C-LiMn_0.8Fe_0.2PO₄ are uniformly covered by a carbon layer of 3 nm,and it can deliver a high discharge capacity of 161 mAh/g at 0.05 C.At the rate of 10 C,the C-LiMn_0.8Fe_0.2PO₄ sample can deliver the specific capacity of 93 mAh/g,and the C-LiMn_0.8Fe_0.2PO₄ has the energy density of 637 Wh/kg.The C-LiMn_0.8Fe_0.2PO₄ can maintain 80.4%of its initial capacity after 900 cycles,it can also maintain 90%and83%of its initial capacity at 45^oC and 55^oC after 100 cycles.The pouch full cell is assembled by the C-LiMn_0.8Fe_0.2PO₄ cathode and SiO_x-C anode,and the capacity retention is 79.5%after 200 cycles at the rate of 0.33 C which has been prelithiated.The purity and conductivity problems of spinel lithium nickel manganese oxide are also discussed in this paper.The influence of preparation process route,high temperature heat treatment condition,doping and coating modification for the materials are also studied systematically.At last,a process of high temperature heat treatment with low temperature annealing has been developed.The cathode material has a specific capacity of 140 mAh/g,and it has no voltage platform of 4.0 V.After Cr-doping and Ag-coating to the optimized material,the compound material of LiNi_0.45Cr_0.05Mn_1.5O₄/Ag has shown better cyclic and rate performance.Three electrodes pouch full cells have been assembled by the LiNi_0.45Cr_0.05Mn_1.5O₄/Ag cathode and different anodes.The prelithiated cell with SiO_x-C anode has the capacity retention of 68.6%after 100 cycles,and the prelithiated cell with graphite anode has the capacity retention of 88.2%after 200 cycles,the cylindrical cell?without prelithiation?with Li₄Ti₅O₁₂2 anode has the retention of 83.4%after 600 cycles.In this paper,it also introduces the P2 type Na-Mn-Fe-O cathode material for sodium ion battery.The rate and cyclic performance have been improved greatly after Ni and Zn doping.At the same time the capacity performance is not affected.The simulated full cell is assembled by the Na_0.67Mn_0.6Fe_0.2Zn_0.1Ni_0.1O₂ cathode and hard carbon anode.The average operating voltage of the cell is above 3.7 V,and the cyclic performance has been further enhanced after presodiation and adjusting the voltage range.In this paper,the P2 type Na-Ni-M-Mn-O?M=None,Zr,Cu?cathode materials are also prepared by acetal decomposition method.At the higher potential range?>4.2 V?,the doping of Cu and Zr can significantly improve the structural stability of the material and alleviate the capacity and voltage decay of Na-Ni-Mn-O system effectively.The initial discharge capacity of the Na_0.67Ni_0.27Cu_0.06Mn_0.67O₂ sample in the potential range of 2.0-4.5 V is 136 mAh/g,and it has the highest capacity retention of96.7%after50cycles.Inthewiderrangeof1.5-4.5V,the Na_0.67Ni_0.27Cu_0.06Mn_0.67O₂ material has the capacity retention of 85%after 30 cycles.The pouch full cell is assembled by the Na_0.67Ni_0.27Cu_0.06Mn_0.67O₂ cathode and hard carbon anode,and it has a capacity of 1.51 Ah.The average operating voltage of the cell is above 3.4 V,and the energy density of the cell is 114 Wh/kg.After 300 cycles,the capacity retention of the cell is 84.5%.At end of the paper,the O3 type cathode material——NaNi_0.5Co_0.2Mn_0.3O₂ for sodium ion battery is introduced.After prepared by Co-precipitation method,the research on characterization and electrochemical properties of the material have been conducted systematically.The results show that in the potential range of 2.0-4.25 V,the specific capacity of the sample is related to the redox couple of Mn³⁺/Mn⁴⁺,Ni²⁺/Ni³⁺?Ni³⁺/Ni⁴⁺,Co³⁺/Co⁴⁺.When charge-discharged at the rate of 0.05 C,the NaNi_0.5Co_0.2Mn_0.3O₂ material can deliver the capacity of 160 mAh/g.The sample also shows good rate performance,even at the rate of 10 C,it can deliver the capacity of80 mAh/g.The NaNi_0.5Co_0.2Mn_0.3O₂ has shown a good cyclic performance when cycled at 0.5 C,97.5%initial capacity can be retented after 50 cycles.The pouch cell with the capacity of 600 mAh has the retention of 87.5%after 300 cycles.