Research On Preparation And Additive Manufacturing Of Hemp Straw-based Carbon Materials For Lithium Ion Battery

To meet the increasing energy demand in the future,there is an urgent need to develop lithium-ion batteries with better performance,among which electrode materials are the key factors affecting battery performance.To overcome the shortcomings of traditional graphite anodes such as low specific capacity and poor cycle stability,anode materials represented by biomass porous carbon have become a hot topic of academic research due to their high specific capacity and wide sources.However,the use of biomass carbon materials is still difficult to overcome the problem that traditional flat plate electrodes cannot have both energy density and power density.Therefore,this article combines pneumatic additive manufacturing technology with the preparation of biomass porous carbon anode materials to construct porous carbon electrodes with special structures to overcome the shortcomings of the traditional flat electrode and further improve the electrochemical performance of lithium-ion batteries.Porous carbon materials were prepared using hemp straw as biomass and zinc chloride as the activator.The effects of different activation ratios and temperatures on the properties of porous carbon materials were investigated.When the activation ratio is 1:5 and the temperature is 600℃,the porous carbon has a specific surface area of822.78 m² g^-1,with an average pore size of 4.97 nm,and has the best electrochemical performance.After 100 cycles at 0.2 C,the capacity reaches 768.11 m Ah g^-1.Using porous carbon materials to configure battery pastes with different solid-liquid ratios,the shear rate apparent viscosity curve was obtained through rheological testing.Through fitting calculations,it can be seen that the Bird-Carreau model can best describe the rheological properties of battery pastes;Set corresponding material model parameters and boundary conditions in polyflow to conduct fluid simulation,explore the impact of extrusion pressure,extrusion diameter,and extrusion head type on the internal flow field of the extrusion head,and provide a reference for subsequent experiments in combination with pre-experimental results.Using a pneumatic additive manufacturing system to construct electrodes,determine process parameters through single-factor experiments,and construct printing electrodes with different layers.The electrochemical test results show that compared to conventional coated electrodes with similar quality,the 0.4 mm spacing single layer printed thin electrode has better cycle performance and rate performance,with a specific capacity of 607.3 m Ah g^-1 after 200 cycles at 2C;Printing multilayer electrodes at the spacing of 0.6 mm significantly increases the specific area capacity of the battery as the number of layers increases.At the rate of 0.2 C,the area capacity of the 6-layer printing electrode reaches 1.43 m Ah cm^-2,which has a higher power density compared to a large mass loaded coated electrode with similar mass.To further improve the electrochemical performance of the electrode,using thiourea as a nitrogen and sulfur source,nitrogen and sulfur double doped porous carbon materials were prepared by impregnation method,with a doping ratio of 1:4.The effects of different doping temperatures on the properties of the materials were investigated.When the doping temperature is 700℃,the specific surface area of the material reaches 1242.81 m² g^-1,and the pore diameter reaches 5.77 nm.After 100cycles at 1C,the specific capacity reaches 764.2 m Ah g^-1;The specific capacity of electrodes printed with doped materials has significantly improved compared to undoped electrodes,but the cyclic stability of 6-layer printed electrodes has decreased.The high specific surface area structure constructed by additive manufacturing technology,combined with the unique porous structure of biomass carbon materials and the synergistic effect of doped elements,effectively improves the performance of batteries,providing more possibilities for the application of biomass carbon materials in high energy and high power density applications.