Preparation And Performance Study Of Li-CO₂ Battery Cathode Materials

Li-CO₂ batteries have received widespread attention in the past 20 years because they are much higher than the theoretical energy density（1876 Wh/kg）of commercial lithium-ion batteries and are environmentally friendly.However,the current Li-CO₂battery has problems such as high over-electric potential,low actual energy density and short cycle life,and there is still a long way to go for real commercial use.Designing and synthesizing more efficient catalysts is the only way to solve these problems at present.Nowadays,precious metal elements such as Pt and Ir are regarded as the best elements for making Li-CO₂ battery cathode materials,but their scarcity and high cost make them doomed to be used on a large scale.Therefore,the development of non-precious metal catalysts is crucial.This thesis mainly uses the cathode materials of transition metals Sn and Cu synthetic lithium-air batteries,and studies their properties.The main research contents are as follows:（1）Preparation and electrochemical performance study of Sn-based materials for battery cathodes（Sn/SnO₂@C）.A Sn-MOF nanoparticle was prepared using the transition metal tin sulfite in combination with the organic substance terephthalic acid,followed by carbonisation to form Sn/SnO₂@C.The nano-shape of the material was analysed using SEM and the formation of Sn/SnO₂@C nanomaterials was confirmed by XPS and XRD.Applying the Sn/SnO₂@C material as the cathode of a Li-CO₂battery,test results showed that the discharge plateau reached approximately 2.63 V and the discharge capacity reached 14,000 mAh/g at a current density of 50 mA/g.（2）Using Balsha wood as the precursor,the Sn-MOF nanosphere particles are grown in the channel of the wood itself,and then carbonized.The three-dimensional self-supporting material modified by Sn/SnO₂@C is prepared,which is directly used as the positive pole of Li-CO₂ battery.Compared with spraying Sn/SnO₂@C on carbon paper,the Sn-MOF material grows inside the wood and then carbonizes it.The obtained electrode material naturally has a wood channel,which is conducive to the transportation of carbon dioxide when the lithium-air battery is working.At the same time,due to the use of Paulownia wood as a precursor,Sn-MOF nanosphere particles are not easy to accumulate at high temperature and can withstand higher temperatures,so that they can be doped with nitrogen.When carbonizing the material,melamine is mixed in,and the material is further nitrogen-dated.With the three-dimensional self-supporting material modified by Sn/SnO₂@C as the positive electrode,the lithium-carbon dioxide battery discharge ratio capacity is as high as 12.86 mAh/cm²,the charging ratio capacity reaches 7.27 mAh/cm²,and the number of cycles is as high as75 times.（3）Using Balshamu as the precursor,Cu-MOF particles are grown on it and carbonized.Cu-MOF has an ortho-polyhedral structure and has excellent specific surface area and pore structure after N-doping.The Li-CO₂ battery with Cu-MOF modified three-dimensional self-supporting material as the anode achieved a discharge specific capacity of over 12 mAh/cm² and a charge specific capacity of 6.69 mAh/cm²after complete discharge,and could be cycled stably for 128 cycles.The above three research contents all select the metal components with transition metals as catalysts,and the cost is low.One of the synthesized cathode materials is powdery,and the other two combine biomass to synthesize three-dimensional materials with self-supporting capabilities.All three research contents have good electrocatalytic performance.Among them,the three-dimensional self-supporting material also has excellent circulation stability.