Synthesis And Modification Of Fe_0.5Co_0.5S₂ Cathode Material For Thermal Batteries

Fe_0.5Co_0.5S₂,combined the advantages of low cost and high voltage of Fe S₂ and high conductivity of Co S₂,has become one of the most promising cathode materials for high-power,long-life and miniaturized thermal batteries.However,traditional preparation methods are either inefficient or difficult to synthesize high-purity Fe_0.5Co_0.5S₂cathode.In addition,the air stability and electrochemical performances of Fe_0.5Co_0.5S₂ cathode materials still need to be further improved.In this paper,Fe_0.5Co_0.5S₂ was synthesized by co-precipitation combined with high temperature solid state method.In addition,it was modified by KH550 and carbon to improve the electrochemical performances and/or air stability.Fe_0.5Co_0.5S₂ was synthesized by co-precipitation combined with high temperature solid state method.When the mass ratio of precursor and sulfur powder was 2:1,the reacted at 500℃for 4h,and then heat treated at 580℃for 2h,the prepared Fe_0.5Co_0.5S₂ exhibited a discharge specific capacity of 693m Ah g^-1 and a specific energy of 1096Wh kg^-1at the cut-off voltage 1.2V.Under pulse discharge model,the voltage can still be maintained at 1.26V after 20 pulses.KH550 modified Fe_0.5Co_0.5S₂ was prepared by a liquid phase method.XRD test results showed that the modification of KH550 had no obvious effect on the phase structure of Fe_0.5Co_0.5S₂.SEM and TEM results showed that KH550 mainly distributed on the surface of Fe_0.5Co_0.5S₂ particles.The electrochemical performances of the as-prepared KH550-modified Fe_0.5Co_0.5S₂increased gradually with the decrease of acetic acid content.The KH550-modified Fe_0.5Co_0.5S₂（FC550-1）prepared with acetic acid content of 1 wt%exhibited the highest discharge specific capacity of739m Ah g^-1 at a cut-off voltage of 1.2 V,which was 46m Ah g^-1 higher than that of the Fe_0.5Co_0.5S₂（FC）cathode.In addition,storage experiments showed that the KH550coating improved the air stability of Fe_0.5Co_0.5S₂.After being stored for one week at100%relative humidity and 30°C,the FC550-1 only showed slightly degradation.The electrochemical performance tests after storage further showed that S-FC550-1can still maintain a specific capacity of 571m Ah g^-1（decay rate 22.7%）with the cut-off voltage 1.2V,while the specific capacity of S-FC in the same environment decayed to 489m Ah g^-1（29.4%decay rate）.Moreover,although the pulse performance of S-FC550-1 showed some attenuation,it was still better than that of S-FC.The carbon-coated Fe_0.5Co_0.5S₂ was successfully synthesized by hydrothermal carbonization combined with heat treatment.XRD showed that the carbon coating had no obvious effect on the phase structure of Fe_0.5Co_0.5S₂.SEM and TEM results showed that the carbon material was uniformly coated on the particle surface with a thickness of about 5 nm.Raman test further showed that the I_D/I_G value of the carbon material obtained by this method was 0.93,with a certain degree of graphitization,which could provide an excellent conductive network for the material.The content of carbon source had an important influence on the electrochemical performance of Fe_0.5Co_0.5S₂.With the increase of the carbon source content,the electrochemical performance first increased and then decreased.Under constant current discharge model,the carbon-coated Fe_0.5Co_0.5S₂（FC-C2）material prepared with a glucose content of 16wt%had the highest discharge performance.The specific capacity can reach 778m Ah g^-1 with the cut-off voltage 1.2V,which was which was 85m Ah g^-1higher than that of the Fe_0.5Co_0.5S₂（FC）.Under pulsed discharge model,the FC-C2material can still maintain a voltage of 1.36V after 20 pulses,while the FC sample has decayed to 1.26V.