【作者】 程静；

【导师】 刘韩星；

【作者基本信息】 武汉理工大学 ， 材料科学与工程， 2021， 硕士

【摘要】 热电池的正极材料是构成热电池的关键组分,其对热电池的容量、工作时间等都有着重要影响。Fe S₂由于存储量大,容量高,是应用较早最广的热电池正极材料,但存在内阻较大、导电性差、热稳定性差等不足之处。具有Fe S₂相似结构的Co S₂内阻小、电导率高且热稳定性好,是比较优良的热单池正极材料,但目前Co S₂主要通过固相法、水热法等方法合成,存在着形貌控制难、成本高、环境污染等问题;此外,Co S₂空气稳定性较差,限制了其在热电池中的实际应用。因此本文通过简单的沉淀法结合高温固相法合成Co S₂,研究了合成工艺对材料结构与电化学性能的影响;同时,采用沉淀法对其进行Fe S₂包覆改性研究,研究了包覆改性对其空气稳定性及电化学性能的影响。本文通过沉淀法和高温固相法结合制备了Co S₂,并研究前驱体溶液的p H值,前驱体反应时间,反应物浓度,高温温度,高温时间对Co S₂形貌、物相及电化学性能等的影响。结果表明前驱体溶液的p H值,高温补硫的反应温度和时间对其放电性能的影响较大。其中前驱体溶液的p H值大于3时,产物中易生成Co₃S₄杂质。在优化条件下合成的Co S₂没有明显杂相,颗粒粒径均一性较好,电化学性能优越。在截止电压为1.2 V时,其所制备的单体电池的恒流放电比容量（比能量）可以达到759 m Ah·g^-1(1204 Wh·kg^-1),脉冲放电时的脉冲个数达到了23个。采用沉淀法合成了Fe S₂@Co S₂,并对其电化学性能及空气稳定性进行了研究。XRD、SEM和TEM等结果显示确实生成了Fe S₂包覆Co S₂的壳核结构。同时,放电结果表明在100 m A·cm^-2电流密度下,随着Fe S₂量的增加,xwt%-Fe S₂@Co S₂（x=0,3,6,9）的放电比容量和比能量先增加而后减少,其中6wt%-Fe S₂@Co S₂的样品放电比容量和比能量最高,在截止电压为1.2 V时,其恒流放电比容量（比能量）可以达到779 m Ah·g^-1(1244 Wh·kg^-1),这要比同样条件下的纯Co S₂的760 m Ah·g^-1(1208 Wh·kg^-1)高。同时,在脉冲条件下6wt%-Fe S₂@Co S₂的脉冲个数为24个,稍高于纯Co S₂的23个。另外,存储后的纯Co S₂的物相中有较多的杂质,而S-6wt%-Fe S₂@Co S₂物相中的杂质较少。对各组分Fe S₂@Co S₂存储后放电测试发现,存储后Fe S₂@Co S₂放电性能明显优于未包覆的纯Co S₂。在截止电压为1.2 V时,S-6wt%-Fe S₂@Co S₂的恒流放电比容量（比能量）可以达到539 m Ah·g^-1(852 Wh·kg^-1),而S-Co S₂仅有205 m Ah·g^-1(293Wh·kg^-1)的放电比容量（比能量）。因此,包覆一定量的Fe S₂可以提高Co S₂的空气稳定性。更多还原

【Abstract】 The cathode materials have important influences on the capacities and working time of the thermal batteries,which have been considered as key component of thermal batteries.Fe S₂is the earliest and most widely used cathode material for thermal batteries due to its large storage capacity and high capacity.However,it has disadvantages such as large internal resistance,poor electrical conductivity and poor thermal stability.Co S₂,which has a similar structure to Fe S₂,has low internal resistance,high conductivity and good thermal stability,so it is a kind of promising cathode material.However,at present,Co S₂is mainly synthesized by solid phase method,hydrothermal method,etc.,which products problems such as difficult topography control,high cost and environmental pollution.In addition,the poor air stability of Co S₂limits its practical application in thermal batteries.Therefore,in this paper,Co S₂was synthesized by simple precipitation combined with high-temperature solid phase method,and the influence of the synthesis process on the structure and electrochemical performance of the material was studied.At the same time,the Fe S₂coating modification of Co S₂was studied by the precipitation method,and the influence of the coating modification on its air stability and electrochemical performances were studied.In this paper,Co S₂was prepared by the combination of the precipitation method and high-temperature solid phase method and the effects of p H value,reaction time,reactant concentration,heating temperature and time on the morphology,phase and electrochemical performances of Co S₂were studied.The results show that the p H value,heating temperature and time have the obvious influences on its discharge performances.When the p H value is greater than 3,Co₃S₄impurities are easily generated in the product.The Co S₂with no obvious impurity phase,good size uniformity and electrochemical performance could be obtained under the optimized conditions.When the cut-off voltage is 1.2 V,constant current discharge specific capacity（specific energy）of the Co S₂can reach 759 m Ah·g^-1(1204 Wh·kg^-1),and the number of pulses during pulse discharge can reache 23.Fe S₂@Co S₂was synthesized by precipitation method,and its electrochemical performances and air stability were studied.The results of XRD,SEM and TEM showed that the core-shell structure of Fe S₂coated Co S₂was indeed formed.At the same time,the discharge results show that at a current density of 100 m A cm^-2,as the amount of FeS₂ increases,the discharge specific capacities and specific energies of xwt%-Fe S₂@Co S₂（x=0,3,6,9）first increase and then decrease,of which6wt%-Fe S₂@Co S₂sample shows the highest discharge specific capacity and specific energy.When the cut-off voltage is 1.2 V,its constant current discharge specific capacity（specific energy）can reach 779 m Ah·g^-1(1244 Wh·kg^-1),which is higher than 760 m Ah·g^-1(1208 Wh·kg^-1)of pure Co S₂under the same conditions.At the same time,the number of pulses of 6wt%-Fe S₂@Co S₂under the pulse condition is 24,which is slightly higher than the 23 of pure Co S₂.In addition,more impurity can be found in pure Co S₂after storage,while less impurity can be found in S-6wt%-Fe S₂@Co S₂.The discharge tests for each component Fe S₂@Co S₂after storage found that the discharge performances of Fe S₂@Co S₂after storage were better than that of uncoated pure Co S₂.When the cut-off voltage is 1.2 V,the constant current discharge specific capacity（specific energy）of S-6wt%-Fe S₂@Co S₂can reach539 m Ah·g^-1(852 Wh·kg^-1),while S-Co S₂only shows 205 m Ah·g^-1(293 Wh·kg^-1)discharge specific capacity（specific energy）.Therefore,coating a certain amount of Fe S₂can improve the air stability of Co S₂.更多还原