Study On Preparation Of Doped Cobalt Ferrite Magnetostrictive Materials From Recycling Waste Lithium Ion Batteries

Lithium ion batteries are widely used in electronic information products and new energy electric vehicles due to their high energy density,good cycle performance,and low self-discharge rate.The increasing consumption of lithium ion batteries leads to the imminent disposal of waste lithium-ion batteries.In the solid waste lithium ion battery,there are a lot of metal resources,if not used will not only cause a waste of resources,the heavy metal elements in the battery into the formation will also pollute the environment.Therefore,cobalt ferrite magnetostrictive materials with higher added value were synthesized by sol-gel-auto-combustion method from waste lithium ion batteries.This process not only lays the foundation for the industrialization of waste lithium ion batteries,but also benefits the sustainable development of the economy,and has a good application prospect.The magnitude of the magnetostriction of cobalt ferrite is measured by the magnetostrictive strain coefficientλand the strain derivative dλ/d H,but the values of these two parameters are not high enough and there is room for improvement.Therefore,in this thesis,the magnetostrictive properties are improved by compounding and doping to meet the needs of applications.The specific research contents and conclusions are as follows:（1）Using waste lithium ion batteries as raw materials,the Mg O composite Co Fe₂O₄ magnetostrictive nanomaterials were synthesized by the sol-gel-auto-combustion method,and the structure,morphology,magnetic properties,and magnetostrictive properties of the composite samples were analyzed;（2）The influence of two metals with different valence states on the magnetostrictive properties of Co Fe₂O₄ was studied on the basis of single metal doping;（3）The influence of co-doping on the morphology,particle size,crystallinity,magnetic properties and magnetostrictive properties of the prepared samples was investigated by co-doping of metal ions in three different valence states.X-ray diffractometer was used to analyze the crystal form and structure of the powdery samples.Field emission scanning electron microscopy（SEM）and high-resolution transmission electron microscopy（HRTEM）were used to determine the morphology of samples,aggregation state,and crystal plane spacing.The Fourier Infrared Spectroscopy（FT-IR）analyzes the functional groups in the sample,and uses X-ray photoelectron spectroscopy（XPS）to determine the valence state of the metal elements contained in the sample and its distribution at the tetrahedral and octahedral positions.Vibrating sample magnetometer（VSM）and magnetostrictive tester can determine the magnetic and magnetostrictive properties of samples at room temperature.Research shows:1 The non-magnetic MgO composite CoFe₂O₄ material is a crystal with a face-centered cubic structure.The minimum particle size of all samples was 34.1 nm.With the increase of Mg O concentration,the microstructure of the composite changed.The characteristic absorption peak caused by tensile vibration of Fe³⁺-O^2-at the tetrahedron around at 576 cm^-1 has a small displacement.The saturation magnetization and maximum magnetostrictive strain derivative of Co Fe₂O₄/Mg O（x=0.02）nanocomposites are 77.35emu·g^-1 and 2.16×10^-9A^-1·m,respectively.These values are about 50%higher than those reported in the literature for changing the magnetostrictive properties of rare earth ion-doped ferrites.At the same time,the magnetic field strength required to achieve the maximum strain derivative is one-ninth that of pure Co Fe₂O₄.2 the magnetic 2Fe³⁺with different doping amounts of Zn²⁺and Zr⁴⁺entered the cubic spinel structure,which made the grain size first decrease and then increase,and the lattice distortion occurred.The grains changed from regular hexagons to amorphous.The spin vibration of the cobalt ferrite octahedral position metal(Fe³⁺-O^2-)shifts with the increase of Zn²⁺and Zr⁴⁺co-doping.At x=0.05,the doped sample achieved the maximum saturation magnetization of 87.56 emu·g^-1,the magnetostriction coefficient of-122.2 ppm,and the strain derivative of-1.81×10^-9A^-1·m.The maximum saturation magnetization was increased compared with the pure one,the strain derivative is increased by about 20%compared with the conventional rare earth doping,and the magnetic field when the maximum strain derivative is obtained is greatly reduced.3 Containing Co²⁺,Al³⁺,Zr⁴⁺doped Fe³⁺into the spinel structure,the grain size of the sample changes,the lattice distortion,the concentration of Co²⁺at the B site decreases first and then increases,which promotes the magnetic and magnetostrictive properties.At x=0.02,the saturation magnetization and magnetostriction of the sample did not change much compared to pure cobalt ferrite,but the increase in the strain derivative value was the highlight in this study,with the highest value reaching-2.15×10^-9A^-1·m,and the minimum magnetic field strength required,which is of great significance for the application of magnetostrictive sensors in low magnetic fields.