The Research On The Thermal Stability And Discharge Performance Of Copper-doped NiS₂ Cathode Materials In High Specific Energy Thermal Battery

Thermal battery is a kind of high-temperature primary battery mainly used for military field with harsh environment.Therefore,there is a high requirement for the performance of the electrode material,and cathode material is the key factor limiting the development of thermal battery.Ni S₂ is considered to be one of the ideal choices of cathode materials for high specific energy thermal battery,due to its excellent theoretical discharge capacity energy and low cost.However,Ni S₂ has the defects such as poor electrical conductivity and thermal stability,which limit its discharge performance.Aiming at the above problems,pure-phase nano-Ni S₂ with different particle sizes was prepared by ball milling-calcination method,and the effect of particle size on its thermal stability and discharge performance was systematically studied.The electrical conductivity and thermal stability of Ni S₂ were improved by Cu doping modification,and its high-temperature electrochemical performance was improved.（1）nanoscale pure Ni S₂ was prepared by a ball milling-calcination method,and the effect of particle size on the thermal stability and discharge performance of nano-Ni S₂ was studied.The research results show that on the one hand nanometerization can shorten the transport distance of Li⁺,improve the electron and ion conduction between cathode material particles,and thus promote the discharge of thermal batteries.But on the other hand,nanometerization increases the surface energy of the material and reduces its thermal stability.Therefore,as the particle size of Ni S₂ decreases,its discharge performance first increases and then decreases.In this paper,Ni S₂-20h（ball milling time is 20 h）with a grain size of 70 nm exhibits the best discharge performance.At a cut-off voltage of 1.5 V,its specific capacity and specific energy reached 516 m Ah g^-1 and 892 Wh kg^-1,respectively.（2）Ni S₂-20h was modified by Cu doping.The effects of Cu doping on the internal structure,electrical conductivity,thermal stability and discharge performance of Ni S₂were investigated.It was found that Cu doping would increase the lattice constant of Ni S₂.In Cu-doped Ni S₂,the Cu element exists in both monovalent and bivalent states,and is dominated by monovalent.In addition,doping with 10 at%of Cu can increase the room-temperature conductivity of Ni S₂ from 6.4 S cm^-1 to 58 S cm^-1,and at the same time increase its thermal decomposition temperature from 510°C to 580°C.It was found Cu-doped Ni S₂ has better high current discharge capability and high temperature discharge capability.Among them,Ni_0.9Cu_0.1S₂ exhibits the best comprehensive discharge performance.Discharged at 500°C and a current density of 0.1 A·cm^-2,with a cut-off voltage of 1.5 V,the discharge specific capacity and specific energy reached653 m Ah g^-1 and 1111 Wh kg^-1,respectively.The discharge specific capacity and specific energy of pure Ni S₂ under the same conditions are only 516 m Ah g^-1 and 892Wh kg^-1.The results of this thesis show that 1)for high-temperature electrochemical systems,the dual effect of nanometerization makes sulfides have a critical grain size with the best discharge performance.2)Appropriate doping can effectively increase the thermal decomposition temperature of nano-sulfides.3)It provides theoretical guidance and application solutions for the application of nano-sulfides in thermal batteries.