Preparation And Properties Of LiCoO₂ Materials

With the rapid development of stealth technology,absorbing materials play an important role in the defense system of modern military weapons.However,most of the traditional absorbing materials can only be suitable for the environment of normal temperature and pressure.Therefore,it is very meaningful to carry out the research and development of absorbing materials suitable for the special environment.In the new wave absorbing material,ceramic material can be used as a kind of high temperature wave absorbing material because of its high temperature resistance,high strength,low expansion coefficient and good chemical stability.At present,ceramic absorbents,such as SiC,Ti₃SiC₂,and four-needle ZnO,are mainly dielectric loss,which solves the problems of high density and single working environment of traditional magnetic absorbents.However,due to its own characteristics,the radar loss in the low-frequency band is small,and there are some problems such as lag in basic research,narrow absorption band,and poor long-term stability at high temperature.These conditions restrict its further application and development.Therefore,it is necessary to study the new absorbing materials to extend the application range.As a traditional electrical material,LiCoO₂ has the potential to be a new type of absorbing material because its conductivity belongs to the semiconductor range.It is a high temperature stable material with a certain degree of oxidation resistance,can be used in a variety of environmental conditions.Because the conductivity of LiCoO₂ lies between the insulator and the conductor,it is beneficial to absorb electromagnetic waves through dielectric loss.Finally,its conductivity can be adjusted through preparation process and doping modification,which is beneficial to the regulation of electromagnetic parameters.In this paper,the dielectric properties of doped LiCoO₂ material at X-band were tested by waveguide method under different conditions.Try to develop a new kind of absorbing material.The main research contents are as follows:The electrical and absorbing properties of Mg²⁺doped LiCoO₂ were discussed and its principle was analyzed.Firstly,comparing with the LiCoO₂ powder doped with Y³⁺,Zn²⁺,Mg²⁺,Mn³⁺and Ni³⁺,the influence of different doped ions on the absorbing properties of the material was analyzed.The Mg-doped LiCoO₂ powder was determined to have higher complex dielectric constant with higher conductivity and higher absorption property,and its principle was discussed.Secondly,the influence of electrical properties of LiCo_1-xMg_xO₂ was studied by controlling the doping content of Mg²⁺ions.The results showed that with the increase of doping content x,the conductivity and complex permittivity of LiCo_1-xMg_xO₂ increased first and then decreased,reaching the maximum value at x=0.06.Finally,the optimum preparation process is determined by controlling sintering temperature and holding time.When the sintering temperature is 900℃,LiCo_0.94Mg_0.06O₂ has the best electrical performance at24 h.Its conductivity reached 1.79×10^-1 S/cm.The real parts of the complex permittivity increased from 4.8 to 16.2 at 8.2 GH,and imaginary parts of the complex permittivity increased from 0.4 to 4.0 at 8.2 GHz.LiCo_0.94Mg_0.06O₂/paraffin exhibits the best microwave absorption properties when the sample thickness is 2.1 mm.the minimal reflection loss reaches-50.4 d B at 9.0 GHz and an effective absorption band width of 1.8 GHz.However,the properties of LiCo_0.94Mg_0.06O₂/paraffin decrease obviously when the sintering temperature reaches 1000℃.To investigate the absorption properties of composite materials prepared with Mg O or ZnO as matrix and LiCo_0.94Mg_0.06O₂ as absorbent.The influence of the sintering temperature and the absorbent content on the microstructure,permittivity and absorption properties of the composites was discussed.LiCo_0.94Mg_0.06O₂/Mg O composites were prepared by high temperature solid phase sintering.There is no chemical change between LiCo_0.94Mg_0.06O₂ and Mg O.The real and imaginary permittivity of the material does not change significantly when the sintering temperature reaches at 900°C or 950°C.The real part of permittivity was enhanced from 23.9-18.2 to 25.1-25.6 at 8.4-12.4 GHz.But the imaginary part of permittivity was stable.When sintering temperature reach at 900°C,40 wt%LiCo_0.94Mg_0.06O₂/Mg O composite with a thickness of 1.6 mm has relatively good absorbing properties,which shows an effective absorption bandwidth in all X-band.As sintering temperature is950°C,the minimal reflection loss of 40 wt%LiCo_0.94Mg_0.06O₂/Mg O composite with a thickness of 1.8 mm reached to-22.6 d B at 10.34 GHz.There is no chemical reaction between LiCo_0.94Mg_0.06O₂ and ZnO.LiCo_0.94Mg_0.06O₂/ZnO composite can be prepared by temperature solid phase sintering.With the increase of the content of LiCo_0.94Mg_0.06O₂,the real and imaginary permittivity of LiCo_0.94Mg_0.06O₂/ZnO composite increased at 900°C.When the content of LiCo_0.94Mg_0.06O₂ is 20 wt%,the minimal reflection loss of composite reached to-50 d B at 11.45 GHz,and an effective absorption bandwidth is 8.6-12.4 GHz.LiCo_0.6M_0.4O₂ solid solution was prepared by doping Mn³⁺and Ni³⁺ions.The effect of Mn and Ni ions substituting Co on the phase transition,microstructure,conductivity,permittivity,absorption properties of LiCo_0.6M_0.4O₂ solid solution was analyzed.The Ni-doped LiCoO₂ powder has higher conductivity,higher complex dielectric constant and higher absorption properties.The effect of electrical properties of LiCo_1-xNi_xO₂ was studied by controlling the doping content of Ni³⁺ions.With the increase of doping content,the conductivity and complex permittivity of LiCo_1-xNi_xO₂increased first and then decreased.When x is equal to 0.6 the permittivity reached maximum value.LiCo_0.4Ni_0.6O₂/paraffin sintered at 900℃for 24 h exhibits ideal electromagnetic absorption capacity when sintering temperature.Moreover,the reflection loss peak of LiCo_0.4Ni_0.6O₂/paraffin reaches-47 d B at 8.6 GHz,and the reflection loss in the whole X-band is less than-5d B.LiCo_0.4Ni_0.6O₂//ZnO composite ceramics were prepared by dry pressure sintering with good chemical compatibility.When the sample thickness is 2.2 mm and the absorbent LiCo_0.4Ni_0.6O₂content is 30wt%,the absorption performance of LiCo_0.4Ni_0.6O₂/ZnO composite reached-38 d B at10.1-12.4 GHz.