Method for preparing core-shell composite sulfide material by two-step method
阅读说明：本技术 一种两步法制备核壳复合型硫化物材料的方法 (Method for preparing core-shell composite sulfide material by two-step method ) 是由 刘志坚 宁慧龙 于 2021-06-25 设计创作，主要内容包括：本发明涉及热电池及常温锂一次电池电极材料的制造领域,具体为一种两步法制备核壳复合型硫化物材料的方法。本发明通过化学镀法在FeS-(2)粉末颗粒表面形成均匀分布的金属钴层,得到前驱材料；然后对前驱体材料进行硫化处理；得到所述核壳复合型硫化物材料。当本发明所制备的外壳二硫化钴占所述核壳复合型硫化物材料总质量的2.5～14.6％时,以所述核壳复合型正极材料为正极材料；组装成热电池后,热电池在520℃工作温度,200mA/cm～(2)电流密度下恒流放电,截止电压为1.6V时,其放电比容量高达331mAh/g。本发明制备操作方法可靠,成本低廉,所得产品具有优异的热稳定性能和电化学性能,便于大规模的工业化生产。(The invention relates to the field of manufacturing of electrode materials of thermal batteries and normal-temperature lithium primary batteries, in particular to a method for preparing a core-shell composite sulfide material by a two-step method. The invention adopts the chemical plating method to prepare FeS 2 Forming a uniformly distributed metal cobalt layer on the surface of the powder particles to obtain a precursor material; then vulcanizing the precursor material; and obtaining the core-shell composite sulfide material. When the shell cobalt disulfide prepared by the method accounts for 2.5-14.6% of the total mass of the core-shell composite sulfide material, taking the core-shell composite cathode material as a cathode material; assembled into a thermoelectricAfter the cell, the thermal cell was operated at 520 ℃ at 200mA/cm 2 The discharge specific capacity of the material is as high as 331mAh/g when the current density is constant current discharge and the cut-off voltage is 1.6V. The preparation method is reliable, the cost is low, and the obtained product has excellent thermal stability and electrochemical performance and is convenient for large-scale industrial production.)
1. A method for preparing a core-shell composite sulfide material by a two-step method; the method is characterized in that: by electroless plating on FeS2Forming a metal cobalt layer on the surface of the powder particles to obtain a precursor material; then vulcanizing the precursor material; and obtaining the core-shell composite sulfide material.
2. The method for preparing the core-shell composite sulfide material by the two-step method according to claim 1; the method is characterized in that: the preparation method comprises the following steps:
step one
Taking a cobalt-containing solution as a raw material; adding complexing agent into the raw materials, stirring to obtain a spare material, adjusting pH to 9-12, and adding natural pyrite and/or FeS2Powder; stirring and adjusting the pH to 9-12; then adding a reducing agent, and then placing the mixture in a water bath kettle; reacting at 55-95 ℃; obtaining a precursor material of the core-shell composite sulfide material after the solution is clarified liquid;
step two
Heating the precursor product of the core-shell composite sulfide material obtained in the step one to 300-490 ℃ in a sulfur-containing atmosphere in a sintering furnace, and keeping the temperature for about 8 hours at different temperature points; and cooling to room temperature along with the furnace to obtain the core-shell composite sulfide material.
3. The method for preparing the core-shell composite sulfide material by the two-step method according to claim 2; the method is characterized in that: the cobalt-containing solution is a cobalt salt solution; the cobalt salt is selected from at least one of cobalt chloride and cobalt sulfate;
the pH is mainly adjusted to be ammonia water or sodium hydroxide solution;
the complexing agent is citric acid;
the reducing agent is hydrazine solution, and the adding speed is adjusted according to the phenomenon of generating bubbles in the plating solution.
4. A two-step process according to claim 2A method for preparing the core-shell composite sulfide material; the method is characterized in that: in the first step, according to the mass ratio, Co: FeS20.11-0.78: 5.1-10.3, preparing cobalt salt and FeS2Fines and/or natural pyrites; in the second step, the heat preservation time at different temperature points is 7-15 h at the temperature of 300, 350, 430, 450 and 490 ℃.
5. The method for preparing the core-shell composite sulfide material by the two-step method according to claim 2; the method is characterized in that: heating to 55-95 ℃ at the heating rate of 5 ℃/min, stirring and preserving heat for one section; after the plating solution becomes clear; solid-liquid separation; and obtaining a precursor of the core-shell composite sulfide material.
6. The method for preparing the core-shell composite sulfide material by the two-step method according to claim 2; the method is characterized in that: in the second step: uniformly mixing the precursor of the core-shell composite sulfide material obtained in the step one with elemental sulfur powder; placing the mixture in a protective atmosphere in a sintering furnace, and placing the mixture in the protective atmosphere in the sintering furnace, wherein the specific operation is as follows: the first stage at 10 ℃ min-1Raising the temperature to 300 ℃ at the heating rate, and keeping the temperature for 7 hours; then entering the second stage at 5 ℃ min-1The temperature of the furnace is raised from 300 ℃ to 350 ℃ at the temperature raising rate, and the temperature is kept for 15 h; the third stage, at 5 ℃ min-1The temperature of the furnace is raised to 430 ℃ from the temperature of the second stage at the temperature raising rate of (1), and the temperature is kept for 15 hours. In the fourth stage, at 5 deg.C/min-1The temperature rise rate of the furnace is to raise the temperature of the furnace from the third stage to 450 ℃ and keep the temperature for 15 hours. The fifth stage, at 5 ℃ min-1The temperature rise rate of (3) is to raise the temperature of the furnace from the temperature of the fourth stage to 490 ℃, and the temperature is kept for 12 hours. And then, furnace cooling is carried out to room temperature. Cooling along with the furnace to obtain the core-shell composite sulfide material; the protective atmosphere is nitrogen or inert atmosphere.
7. The method for preparing the core-shell composite sulfide material by the two-step method according to claim 2; the method is characterized in that: according to the mass ratio, the precursor of the core-shell composite sulfide material is as follows: 1-12% of elemental sulfur: 3-8; and (3) uniformly mixing the precursor of the core-shell composite sulfide material obtained in the step one with elemental sulfur.
8. The method for preparing the core-shell composite sulfide material by the two-step method according to claim 2; the method is characterized in that: the core of the prepared core-shell composite sulfide material is iron disulfide, and the shell is compact cobalt disulfide.
9. The method for preparing the core-shell composite sulfide material by the two-step method according to claim 8; the method is characterized in that:
in the prepared core-shell composite sulfide material, the cobalt disulfide of the shell accounts for 0.25-60% of the total mass of the core-shell composite sulfide material, and the granularity of the core is 0.5-65.0 microns.
10. The method for preparing the core-shell composite sulfide material by the two-step method according to claim 9; the method is characterized in that: when the prepared shell cobalt disulfide accounts for 2.5-14.6% of the total mass of the core-shell composite sulfide material, taking Li-B alloy as a negative electrode material, LiCl-LiBr-KBr as an electrolyte and nano MgO as isolation powder; taking the core-shell composite type positive electrode material as a positive electrode material; after the thermal battery is assembled, the thermal battery works at the working temperature of 520 ℃ and the working temperature of 200mA/cm2The discharge specific capacity of the material is as high as 331mAh/g when the current density is constant current discharge and the cut-off voltage is 1.6V.
Technical Field
The invention relates to the field of manufacturing of electrode materials of thermal batteries and normal-temperature lithium primary batteries, in particular to a method for preparing a core-shell composite sulfide material by a two-step method.
Technical Field
The thermal battery is a special battery using molten salt as electrolyte, and has the advantages of high power density, high energy density, long storage time and quick activationFast and reliable, is suitable for various harsh working conditions, and is simple and convenient to use. Therefore, the power supply is mainly used as the power supply of high and new technology weapons such as missiles, guided bombs, torpedoes and the like. In the civil field, the thermal battery has wide application prospect as an emergency power supply of an airplane, a power supply of underground high-temperature prospecting equipment and a fire alarm power supply. The anode material widely used at present is mainly natural pyrite iron disulfide (FeS)2). The material has moderate capacity, moderate discharge voltage and low price. The problem is that the performance is related to the choice of the site. Particularly, with the increase of the activity of the negative electrode material of the thermal battery (from Li-Al, Li-Si to Li-B alloy) and the application of the all-lithium electrolyte, the operating temperature of the thermal battery is greatly increased, the requirements of specific power and specific energy indexes are also continuously increased, the thermal decomposition temperature of iron disulfide (550 ℃) is low, the internal resistance is high, the self-discharge is serious and the like, so that the problems become extremely prominent. Becoming a new bottleneck problem. The thermal decomposition temperature of the cobalt disulfide is high (650 ℃), and the internal resistance is small. Is stable in high-temperature molten salt electrolyte, and can obviously improve the effective discharge capacity and power characteristic of the thermal battery. However, cobalt disulfide can only be synthesized artificially, and the cobalt raw material is more expensive than iron. Except that the thermal battery which has special requirements uses the cobalt disulfide as the anode material, the price and the performance can be considered after the cobalt disulfide and the iron disulfide are mixed, and the method is a compromise method adopted by the current thermal battery manufacturers. The principle of the method is that firstly, the iron disulfide with slightly high voltage is used as main discharge, and then the cobalt disulfide with slightly low voltage is used as main discharge. Thereby reducing the risk of thermal instability and improving the effective discharge capacity. The method requires the same amount of the two to produce effective effect. And the intrinsic disadvantages associated with iron disulfide are not completely eliminated. In addition, iron disulfide is often used as a positive electrode material of a lithium primary battery for research and application, so that it is a valuable research work to discuss the electrochemical performance of a core-shell type sulfide composite material as a positive electrode active material of the lithium primary battery.
FeS has been successfully prepared in the laboratory by a hydrothermal method2@CoS2The composite material and the hydrothermal method preparation material technology need to be carried out in a high-temperature and sealed reaction kettle, the dependence of the reaction process on experimental equipment is strong, and the reaction process has strong dependence on experimental reactionThe observation and monitoring of the process and the controllability of the experimental technology are difficult, the batch is small, the danger is high, and the realization of the industrial target with high cost performance is difficult. Therefore, a synthesis method with less difficulty and better material performance needs to be explored to ensure that the FeS can be obtained2@CoS2The novel positive electrode material is accepted in the market. In this chapter, new experimental thought is adopted to complete CoS2For FeS2The coating modification of (3). Firstly, adopting a catalyst-free powder chemical plating technology to perform chemical plating on FeS2Depositing a layer of metal cobalt on the surface of the powder as a precursor with a core-shell structure (first step), and then vulcanizing cobalt particles in a shell layer into CoS by adopting a high-temperature vulcanization technology2Shell (second step), the final shell obtained is CoS2The kernel is FeS2FeS of2@CoS2. The method bypasses the requirements of a hydrothermal method on high-temperature and high-pressure conditions so as to realize the future low-cost preparation of FeS2@CoS2Composite material, herein referred to as FeS Synthesis by two-step Process2@CoS2A composite material.
Disclosure of Invention
The inventor considers that the electrochemical characteristics of the cathode material are determined by the surface state of the material, so the idea that the shell is cobalt disulfide and the core is an iron disulfide core-shell structure is provided, and the idea that the cathode material mainly comprises cheap iron disulfide but has the performance close to that of the expensive cobalt disulfide is tried to be realized. To realize the design function, the outer shell has to be complete and stable in crystal structure, tight and reliable in cladding, firm in core-shell combination and adjustable in wrapping thickness. The core material still uses natural pyrite, and the realization process is not difficult.
The invention provides a method for forming a metal cobalt layer on the surface of iron disulfide of an inner core by adopting a mode of firstly chemically plating cobalt, then carrying out vulcanization treatment on the metal cobalt of a shell layer, and finally obtaining a shell coating layer with cobalt disulfide uniformly distributed. And the cladding is firmer and more reliable.
The invention relates to a method for preparing a core-shell composite sulfide material by a two-step method; by electroless plating on FeS2Forming a metal cobalt layer on the surface of the powder particles to obtain a precursor material; then vulcanizing the precursor material; obtaining the core shellA composite sulfide material.
The invention relates to a method for preparing a core-shell composite sulfide material by a two-step method; the preparation method comprises the following steps:
step one
Taking a cobalt-containing solution as a raw material; adding complexing agent into raw materials, stirring to obtain stock, adjusting pH to 9-12, preferably 10.8-11.2, and more preferably 11, and adding natural pyrite and/or FeS into the stock2Powder; stirring and adjusting the pH to 9-12, preferably 10.8-11.2, more preferably 11; then adding a reducing agent, and then placing the mixture in a water bath kettle; reacting at 55-95 deg.C, preferably 60-85 deg.C; obtaining a precursor material of the core-shell composite sulfide material after the solution is clarified liquid; the cobalt source in the cobalt solution comprises sulfate, chloride and the like;
step two
Heating the precursor product of the core-shell composite sulfide material obtained in the step one to 300-490 ℃ in a sulfur-containing atmosphere in a sintering furnace, and keeping the temperature for about 8 hours at different temperature points; cooling to room temperature along with the furnace to obtain the core-shell composite sulfide material;
the invention relates to a method for preparing a core-shell composite sulfide material by a two-step method; natural pyrite and/or FeS2The particle size of the powder is 1.0 to 57.2. mu.m, preferably 4.9 to 10.1. mu.m, and more preferably 6.7 to 7.9. mu.m. Preferably, natural pyrite and/or FeS is used2The powder needs to be subjected to acidification pretreatment. The acidification pretreatment process comprises (1) taking 10g of natural pyrite or FeS2Placing the powder with specification amount in dilute hydrochloric acid with volume fraction of 8% (volume of dilute hydrochloric acid solution is 80mL) for ultrasonic cleaning for 30 min; (2) after the cleaning is finished, washing the sample by using deionized water (more than 3 times); (3) drying the cleaned sample in a drying oven at 80 ℃ for 4h to finally obtain the pyrite and/or FeS for chemical plating2And (3) powder. The powder may then be electroless cobalt plated.
The invention relates to a method for preparing a core-shell composite sulfide material by a two-step method; the cobalt-containing solution is a cobalt salt solution; the cobalt salt is selected from at least one of cobalt chloride and cobalt sulfate;
the pH is mainly adjusted to be ammonia water or sodium hydroxide solution;
the complexing agent is citric acid;
the reducing agent is hydrazine solution, and the adding speed is adjusted according to the phenomenon of generating bubbles in the plating solution.
The invention relates to a method for preparing a core-shell composite sulfide material by a two-step method; in the first step, according to the mass ratio, Co: FeS20.11-0.78: 5.1-10.3, preparing cobalt salt and FeS2Fines and/or natural pyrites; in the second step, the heat preservation time at different temperature points is 7-15 h at the temperature of 300, 350, 430, 450 and 490 ℃.
The invention relates to a method for preparing a core-shell composite sulfide material by a two-step method; heating to 55-95 ℃ at the heating rate of 5 ℃/min, stirring and preserving heat for one section; after the plating solution becomes clear; solid-liquid separation; and obtaining a precursor of the core-shell composite sulfide material.
The invention relates to a method for preparing a core-shell composite sulfide material by a two-step method; in the second step: uniformly mixing the precursor of the core-shell composite sulfide material obtained in the step one with elemental sulfur powder; placing the mixture in a protective atmosphere in a sintering furnace, and placing the mixture in the protective atmosphere in the sintering furnace, wherein the specific operation is as follows: the first stage at 10 ℃ min-1Raising the temperature to 300 ℃ at the heating rate, and keeping the temperature for 7 hours; then entering the second stage at 5 ℃ min-1The temperature of the furnace is raised from 300 ℃ to 350 ℃ at the temperature raising rate, and the temperature is kept for 15 h; the third stage, at 5 ℃ min-1The temperature of the furnace is raised to 430 ℃ from the temperature of the second stage at the temperature raising rate of (1), and the temperature is kept for 15 hours. In the fourth stage, at 5 deg.C/min-1The temperature rise rate of the furnace is to raise the temperature of the furnace from the third stage to 450 ℃ and keep the temperature for 15 hours. The fifth stage, at 5 ℃ min-1The temperature rise rate of (3) is to raise the temperature of the furnace from the temperature of the fourth stage to 490 ℃, and the temperature is kept for 12 hours. And then, furnace cooling is carried out to room temperature. And cooling along with the furnace to obtain the core-shell composite sulfide material. The protective atmosphere is nitrogen or inert atmosphere.
The invention relates to a method for preparing a core-shell composite sulfide material by a two-step method; according to the mass ratio, the precursor of the core-shell composite sulfide material is as follows: 1-12% of elemental sulfur: 3-8; and (3) uniformly mixing the precursor of the core-shell composite sulfide material obtained in the step one with elemental sulfur.
The invention relates to a method for preparing a core-shell composite sulfide material by a two-step method; the core of the prepared core-shell composite sulfide material is iron disulfide, and the shell is compact cobalt disulfide. The particle size of the core is 1.0 to 57.2 microns, preferably 4.9 to 10.1 microns, and more preferably 6.7 to 7.9 microns.
The invention relates to a method for preparing a core-shell composite sulfide material by a two-step method; in the prepared core-shell composite sulfide material, the shell cobalt disulfide accounts for 0.25-60% of the total mass of the core-shell composite sulfide material, preferably 0.25-14.7%, and further preferably 2.5-14.6%. In industrial application, the content of cobalt disulfide in the product is controlled by controlling the content of cobalt salt in the plating solution, controlling the content of metal cobalt in the plating layer and finally controlling elemental sulfur powder and other reaction parameters. And the particle size of the core is 1.0 to 57.2 microns, preferably 4.9 to 10.1 microns, and more preferably 6.7 to 7.9 microns.
The invention relates to a method for preparing a core-shell composite sulfide material by a two-step method; when the prepared shell cobalt disulfide accounts for 2.5-14.6% of the total mass of the core-shell composite sulfide material, taking Li-B alloy as a negative electrode material, LiCl-LiBr-KBr as an electrolyte and nano MgO as isolation powder; taking the core-shell composite type positive electrode material as a positive electrode material; after the thermal battery is assembled, the thermal battery works at the working temperature of 520 ℃ and the working temperature of 200mA/cm2The discharge specific capacity of the material is as high as 331mAh/g when the current density is constant current discharge and the cut-off voltage is 1.6V.
When the core-shell composite cathode material is prepared, the adopted coating method is that firstly, a cobalt source (including chloride and sulfate) is adopted, and a chemical cobalt plating reaction is adopted to form a metal cobalt particle coating layer on the surface of iron disulfide powder particles. The product is then sulphurized. Because the metal cobalt layer is prepared by chemical cobalt plating reaction, the metal cobalt causes the epitaxial growth of the material in the process of vulcanization, so that the cladding is more uniform, compact and effective. And because the chemical cobalt plating layer is firmly attached to the surface of the iron disulfide particles, the subsequent sulfuration can cause the elements in the cobalt disulfide phase and the iron disulfide phase to have micro mutual diffusion to form a stable blended interface layer. Thereby the core-shell type material has more stable structure and firmer combination.
The main advantages of the technical scheme are as follows:
mineral iron disulfide is generally not high in purity and poor in thermal stability, and artificially synthesized iron disulfide is generally easy to thermally decompose when the temperature is high. The former artificial synthesis method of cobalt disulfide is usually a hydrothermal method or a high-temperature solid-phase synthesis method, the hydrothermal synthesis of cobalt disulfide is usually carried out in a shell-empty manner, and the like, so that the thermal stability is reduced, the solid-phase synthesis of cobalt disulfide usually needs a lot of time, and in the solid-phase synthesis, when large-batch production of cobalt disulfide is carried out, pure-phase cobalt disulfide is often difficult to obtain, and sulfur is taken as sulfur steam during solid-phase synthesis and hardly permeates into the interior of large-batch powder. The experiment adopts a mode of chemical cobalt plating and then vulcanization, the utilization rate of cobalt salt can be improved by a chemical cobalt plating method in the early stage, and the combination of a cobalt plating layer of the chemical cobalt plating and the iron disulfide of the inner core is very stable. After sulfurization treatment by adding sulfur, high-purity cobalt disulfide can be obtained and can be particularly firmly attached to the surface of iron disulfide particles, thereby forming the core-shell type sulfide composite material. The iron disulfide is used as the inner core of the material, and can be used as a source point of autocatalysis when the cobalt is chemically plated, so that a substance containing palladium does not need to be added as an activating agent. Meanwhile, the temperature of the vulcanization reaction does not exceed the thermal decomposition temperature of the iron disulfide, so that the self structure of the iron disulfide is not damaged in the processes of chemical cobalt plating and vulcanization treatment.
The thermal stability of the core-shell material prepared by the invention is obviously improved, and compared with pure iron disulfide, the thermal decomposition temperature is increased from 550 ℃ to 592-640 ℃; the room temperature conductivity of the material is obviously improved, and compared with pure iron disulfide, the room temperature conductivity is increased by orders of magnitude; the specific power characteristic of the thermal battery is improved by reducing the internal resistance of the thermal battery when the material is discharged; the self-loss of the thermal battery is reduced when the material is discharged, and the discharge voltage platform characteristic is obviously improved. The effective discharge capacity of the battery is obviously improved. The preparation method has the advantages of high utilization rate, mild preparation conditions and low production risk, is suitable for large-scale production, and has a significant key effect on improving the cost performance of thermal battery materials or room-temperature lithium primary batteries.
Drawings
FIG. 1 shows FeS prepared at different bath concentrations in example series 12SEM image of electroless cobalt plating product, wherein (a) is CoSO4Has a concentration of 6.5gL-1SEM image of the precursor obtained; (b) is CoSO4Has a concentration of 9.9gL-1SEM image of the precursor obtained; (c) is CoSO4Has a concentration of 13.2gL-1SEM image of the precursor obtained; (d) is CoSO4Has a concentration of 14.3gL-1SEM image of the precursor obtained; (e) is 6.5gL-1EDS spectrum of the precursor obtained under the condition;
FIG. 2 is an SEM image of FeS2 cobalt plated products prepared at different temperatures in example series 2; wherein (a) is SEM picture of precursor obtained when the temperature of the plating solution is 55 ℃; (b) is SEM picture of the precursor obtained when the temperature of the plating solution is 65 ℃; (c) is SEM picture of the precursor obtained when the temperature of the plating solution is 75 ℃; (d) is SEM picture of the precursor obtained when the temperature of the plating solution is 85 ℃; (e) is SEM picture of the precursor obtained when the temperature of the plating solution is 95 ℃; (f) a graph of reaction temperature versus reaction time;
FIG. 3 is an SEM image of FeS2 cobalt plated products prepared by performing series 3 at different pH values; wherein, the picture (a) is an SEM picture of the precursor obtained when the pH is equal to 8; FIG. (b) is an SEM image of the precursor obtained at pH 9; FIG. (c) is an SEM image of the precursor obtained at a pH of 10; FIG. d is an SEM image of the precursor obtained at pH 11; panel (e) is an SEM image of the resulting precursor at pH 12; FIG. f is an SEM image of the precursor obtained at pH 13;
FIG. 4 is an SEM image of FeS2 cobalt plated products prepared at different hydrazine concentrations in example series 4; wherein the hydrazine concentration is 8ml in graph (a)-1SEM image of the precursor obtained; FIG. b shows the hydrazine concentration at 10ml-1SEM image of the precursor obtained; FIG. C shows hydrazineThe concentration is 12ml-1SEM image of the precursor obtained; FIG. (d) shows a hydrazine concentration of 14ml-1SEM image of the precursor obtained; graph (e) shows the hydrazine concentration at 16mLL-1SEM image of the precursor obtained; graph (f) is a graph of hydrazine concentration versus reaction time;
FIG. 5 shows FeS obtained in examples 5 to 72XRD spectrogram of the electroless cobalt plating product;
FIG. 6 is an XRD diffraction of samples of example 5 at different sulfiding temperatures (a)350, 390, 430, 450 and 490 ℃; (b) partial XRD enlarged spectrogram;
FIG. 7 is an SEM of the morphology of the products of examples 5 to 7 after sulfidation (a) CP-1; (b) CP-2; (c) CP-3 and (d) solid phase Synthesis of CoS2
FIG. 8 is a graph showing the discharge characteristics of FeS2, MIX, CP-1, CP-2, and CP-3 at 520 ℃ and a current density of 200mA cm-2, wherein (a) is the specific capacity at a cut-off voltage of 1.6V.
Fig. 9 is an enlarged view of fig. 8 a.
Detailed Description
In the embodiment, the acidification pretreatment process is (1) taking 10g of natural pyrite or FeS2Placing the powder with specification amount in dilute hydrochloric acid with volume fraction of 8% (volume of dilute hydrochloric acid solution is 80mL) for ultrasonic cleaning for 30 min; (2) after the cleaning is finished, washing the sample by using deionized water (more than 3 times); (3) drying the cleaned sample in a drying oven at 80 ℃ for 4h to finally obtain the pyrite and/or FeS for chemical plating2And (3) powder. The powder may then be electroless cobalt plated.
Series of implementation 1
Optimization of precursor preparation conditions-CoSO4Optimisation of concentration
Taking a cobalt-containing solution as a raw material; firstly, adding complexing agent into raw material, stirring to obtain standby material, regulating pH to 11, then adding FeS into standby material2Powder; stirring and adjusting the pH to 11; then adding a reducing agent (80% hydrazine), and then placing the mixture in a water bath kettle; reacting at 75 ℃; obtaining the core-shell composite sulfide material after the solution is clarified liquidA bulk material;
investigation of concentration conditions:
the concentrations of the components are respectively 6.5, 9.9, 13.2 and 14.3 g.L-1CoSO of4And (3) carrying out a comparative experiment, wherein in the experimental process, other raw materials and experimental condition parameters are respectively as follows: the concentration of 80% hydrazine is 12 mL. L-1The pH value of the plating solution is 11, the temperature of the plating solution is 75 ℃, and the temperature of CoSO4The amount of the solution was 200mL, FeS2Mass 20g, C6H8O7·H2The mass of O was 10 g. Different CoSO4FeS coated with metallic Co particles obtained by chemical cobalt plating at concentration2The morphology of the material is shown in figure 1; as can be seen from the figure, with CoSO4The particle size of the metallic Co particles gradually becomes larger as the solution concentration increases. As can be seen from FIG. 1(a), when CoSO is used4The concentration is 6.5gL-1Hour FeS2The metal Co particles coated on the surface of the powder are relatively less and are distributed unevenly. With the gradual increase of the concentration, the coating particles on the surface of the powder become larger, the distribution is more uniform, and the particle size is more uniform (as shown in fig. 1 (b)). However, when the concentration is as high as 13.2gL-1Then FeS2The plating particles on the surface rapidly increase, causing the plating layer surface particles to be coarse and rough (fig. 1 (c)). When CoSO4The concentration reaches 14.3gL-1Then FeS2The metallic Co particles coated on the surface of the powder were aggregated in a large amount (FIG. 1(d)), and it was found by EDS spectroscopy (FIG. 1(e)) that FeS was present2The material attached to the surface of the particles is metal Co. The reaction speed is increased when the concentration is increased, and the experimental process shows that bubbles generated in the plating solution are increased, the time from the chemical cobalt plating reaction to the reaction solution changing into the clear solution is short (as shown in figure 1 (f)), and the excessive CoSO4The concentration is easy to cause the FeS as the matrix material2Co particles on the surface are seriously deposited locally, the distribution uniformity is not good enough, and CoSO can be obtained by comprehensive analysis4The optimal concentration of the plating solution is 9.9-13.2 gL-1。
Thus, the concentration of the active ingredient is 9.9-13.2 gL-1The concentration of (2) is selected to be 12 g.L-1Concentration of (CoSO)4) As a next step of the study (see example series 2)
Series of implementation 2
Optimization of precursor preparation conditions-optimization of plating solution temperature (i.e. plating temperature)
The treatment steps were identical to those of the series 1;
taking the concentration as 12gL-1CoSO of4200mL of acidified pretreated FeS with 20g2The powder was used as a raw material, and the plating solution temperatures were set to 55, 65, 75, 85 and 95 ℃ respectively, and NaOH and ammonia were used to adjust the pH of the plating solution to 11. The Co cladding morphologies obtained at different temperatures are greatly different, and the morphology graph is shown in FIG. 2.
As can be seen in FIGS. 2(a-e), the reaction temperature was too low (55 ℃ C.), and no significant morphology of Co particles appeared (FIG. 2 (a)). At a reaction temperature of 65 ℃, a small amount of Co particles appear (FIG. 2(b)), but the reaction requires a long reaction time, and the oxidation of metallic cobalt is caused by a large amount of air dissolved in the plating solution due to the long reaction time. The temperature of the plating solution is increased (75 ℃), and the Co particles in the coating are distributed more uniformly (figure 2 (c)); when the temperature of the plating solution is 85 ℃, Co particles are in FeS2The surface aggregates into larger particles (fig. 2 (d)). When the temperature of the plating solution is 95 ℃, Co particles are in FeS2The phenomenon of surface agglomeration into larger particles is more severe (fig. 2(e)), and there is a phenomenon that metallic cobalt is reduced without being deposited on the base FeS2Surface, FIG. 2(d)1) The silver white particles in the silver paste are metallic cobalt. Too high a temperature (especially if the temperature of the plating solution exceeds 95 ℃) also leads to excessive volatilization of ammonia. The relationship between the reaction times at different plating solution temperatures is shown in FIG. 2(f), in which it can be seen that the time required for the electroless cobalt plating reaction to reach a clear solution becomes shorter as the electroless plating reaction temperature increases. Combining the above analysis, the optimal plating solution temperature of 75 ℃ was determined.
Series of implementation 3
Optimization of precursor preparation conditions-optimization of bath pH
The treatment steps were identical to those of the series 1;
the reaction temperature is set to 75 ℃ in the experiment, and the concentration is taken to be 12gL-1CoSO of4200mL and 20g acidified pretreated FeS2The powder was used as a starting material and the reactions were examined at pH 8, 9, 10, 11, 12 and 13. During the chemical plating reaction, the pH value of the plating solution is reduced. To maintainThe pH value of the plating solution is not changed, the pH value of the plating solution is controlled by continuously adding sodium hydroxide solution or ammonia water in the experiment, the appearance is shown in figure 3, and the condition that the pH value is gradually increased from 8 and the matrix FeS is obtained2The particle size of the particles at the local position of the surface is increased. FeS when the pH increased to 132The particle diameter of the particles at the partial position appearing on the surface is small, and FeS2The surface had a rugged corrosion phenomenon (FIG. 3(f)), and the higher the pH, the more severe the corrosion was, since the excessively strong alkaline bath was associated with FeS2S in (1) is reacted. Thus, increasing the pH of the bath appropriately increases the reaction rate, while too high a pH leads to increased reaction rate and particles that are too large, and Co (OH) is produced2Is not beneficial to the subsequent sulfuration reaction. Finally, the optimum pH was determined to be 11.
Series of implementation 4
Optimization of precursor preparation conditions-optimization of reducing agent concentration (optimization of hydrazine concentration)
The treatment steps were identical to those of the series 1;
using L concentrations of 8, 10, 12, 14 and 16mL respectively-1The influence of hydrazine concentration on the Co coating is researched by taking 80% hydrazine as a selection item, and other experimental conditions are the same as above.
FIG. 4 shows hydrazine concentrations of 8, 10, 12, 14 and 16mL L-1Cobalt coated FeS prepared under conditions2SEM image of powder. The lower hydrazine concentration (8mL L) can be seen in FIG. 4(a)-1) To Co2+Is less reducing, FeS2The surface exhibited only a trace of fine Co particles. As the concentration increases, the grains also increase ((fig. 4 (b-d))). But when the concentration increased to 16mL L-1In this case (FIG. 4(e)), the Co particles did not have a large particle size, but the grown Co particles were agglomerated seriously.
Example 5
A vulcanization experiment of a precursor with low cobalt concentration;
the preparation process of the precursor is consistent with that of example 1, and the specific condition parameters are as follows:
the reaction temperature is set to be 75 ℃ in the experiment, and the concentration is taken to be 12 g.L-1CoSO of454 ml and 20g acidified pretreated FeS2Powder ofFor the raw material, the pH value at 11 was studied respectively; stirring; then heating to 60-85 ℃ at the heating rate of 5 ℃/min in a water bath solution, stirring and preserving heat for a period of time; after the plating solution becomes clear; solid-liquid separation; and obtaining a precursor of the core-shell composite sulfide material. The phase analysis of the obtained electroless cobalt plating product is shown in FIG. 5 as CP-1 (Co).
Adding simple substance sulfur powder into the prepared product, carrying out vulcanization reaction (enough sulfur powder), and carrying out a first stage at 10 ℃ for min-1Raising the temperature to 300 ℃ at the heating rate, and keeping the temperature for 7 hours; then entering the second stage at 5 deg.C for min-1The temperature of the furnace is raised from 300 ℃ to 350 ℃ at the temperature raising rate, and the temperature is kept for 15 h; the third stage, at 5 deg.C for min-1The temperature of the furnace is raised to 430 ℃ from the temperature of the second stage at the temperature raising rate of (1), and the temperature is kept for 15 hours. The fourth stage, at 5 deg.C for min-1The temperature rise rate of the furnace is to raise the temperature of the furnace from the third stage to 450 ℃ and keep the temperature for 15 hours. The fifth stage, at 5 deg.C for min-1The temperature rise rate of (3) is to raise the temperature of the furnace from the temperature of the fourth stage to 490 ℃, and the temperature is kept for 12 hours. And then, furnace cooling is carried out to room temperature.
Thus obtaining a two-step preparation of CoS2Coated FeS2Product (FeS)2@CoS2). The obtained core-shell sulfide composite was designated as (CP-1). (product phase is shown in FIG. 6)
The melting point of sulfur was 112.8 ℃ and the boiling point was 444.6 ℃. The cobalt sulfidation process, from the particle surface to the interior, has S/CoS2Liquid-solid reaction, CoS2/Co3S4Solid-solid reaction, Co3S4/Co9S8Solid-solid reaction, Co9S8Solid-solid reaction of Co. In the series of reactions, the reaction rate of solid-solid reaction is slower, the reaction rate can be accelerated by increasing the temperature, but the gaseous sulfur has larger loss in the reaction process under the influence of the boiling point of the sulfur. Especially of Co3S4The melting point is low, and the reaction heat of the fine cobalt powder and sulfur can cause the local temperature to rise to reach Co3S4Above the melting point, the high surface characteristics of the artificially synthesized fine powder are destroyed. Therefore, considering the several factors, the synthesis of the cobalt disulfide can only be carried out under the condition of lower temperature, and the external release of the reaction heat is also consideredWith considerable difficulty. The pure cobalt shell is vulcanized, and the reaction heat usually does not cause abnormal rise of the powder temperature because the cobalt equivalent is small during vulcanization. However, the following problems need to be considered: the particles of the chemical plating are attached to the surface of the iron disulfide, and whether the phase expansion caused by temperature rise and reaction can cause the plating layer of the precursor and the cobalt disulfide plating layer to fall off or not is judged. Whether the cobalt disulfide plating layer generates holes or not. After high-temperature vulcanization, the shell layer is more uniform or more nonuniform, the reaction can be completely finished under the condition of compactness, and the base material FeS is subjected to long-time high-temperature treatment2Whether it is still in a steady state. Based on these problems, process conditions need to be optimized. Firstly, a vulcanized sample is placed at 300 ℃ for heat preservation for a period of time, under the condition, the sulfur powder is completely converted from solid state to liquid state, and the purpose is to enable sulfur to pass through tiny gaps among cobalt particles in a cobalt-plated layer within sufficient time, so that the gaps among the cobalt particles in a shell layer are completely filled. And then to 350 c, at which time the reactions at the several interfaces described above can proceed, but at a slow rate, in order to allow a smooth, coordinated transition in the difference in core-shell expansion. The sulfur powder consumed by the internal reaction is continuously supplemented from the outside. The XRD pattern of the product sample obtained at 350 ℃ shows that trace CoS exists2Formation of, and also mesophase Co3S4Is present. When the vulcanization temperature reaches 430 ℃, CoS2The characteristic diffraction peak of the cobalt disulfide is obvious in the map, and the crystal integrity of the obtained cobalt disulfide is similar to that of the obtained cobalt disulfide when the vulcanization temperature is increased to 450 ℃. Under these conditions, the substrate FeS2The phase of (A) was not damaged and no decomposition products were present. The results of this are equal to Sun Xiong[117]CoS synthesis by solid phase method2The obtained material phase is the same. When the reaction is carried out at 490 c, the amount of cobalt disulfide synthesized decreases because the temperature is far above the boiling point of sulfur (444.6 c), and the effective sulfur powder of the reaction decreases greatly, so that the synthesis temperature is controlled to be around the boiling point of sulfur.
And respectively taking the core-shell material and the iron disulfide as anode materials to prepare the single thermal battery. The diameter of the single battery is 17mm, the thickness of the single battery is 2mm, and the cathode of the single battery is Li-B. The current density is 200mA cm-2In time, the core-shell material is effectively dischargedCompared with iron disulfide, the platform is prolonged by 6.9%, and the effective specific capacity is increased by 69mA h g-1The internal resistance was reduced by 10.7% (see fig. 8).
Example 6
Carrying out a vulcanization experiment on a precursor with higher cobalt concentration;
the preparation process of the precursor is consistent with that of example 1, and the specific condition parameters are as follows:
the reaction temperature is set to be 75 ℃ in the experiment, and the concentration is taken to be 12 g.L-1CoSO of4110 ml and 20g acidified pretreated FeS2The powder is used as a raw material, and the pH value is respectively researched to be 11; stirring; then heating to 60-85 ℃ at the heating rate of 5 ℃/min in a water bath solution, stirring and preserving heat for a period of time; after the plating solution becomes clear; solid-liquid separation; and obtaining a precursor of the core-shell composite sulfide material. The phase analysis of the obtained electroless cobalt plating product is shown in FIG. 5, CP-2 (Co).
Adding simple substance sulfur powder into the prepared product, carrying out vulcanization reaction (enough sulfur powder), and carrying out a first stage at 10 ℃ for min-1Raising the temperature to 300 ℃ at the heating rate, and keeping the temperature for 7 hours; then entering the second stage at 5 deg.C for min-1The temperature of the furnace is raised from 300 ℃ to 350 ℃ at the temperature raising rate, and the temperature is kept for 15 h; the third stage, at 5 deg.C for min-1The temperature of the furnace is raised to 430 ℃ from the temperature of the second stage at the temperature raising rate of (1), and the temperature is kept for 15 hours. The fourth stage, at 5 deg.C for min-1The temperature rise rate of the furnace is to raise the temperature of the furnace from the third stage to 450 ℃ and keep the temperature for 15 hours. The fifth stage, at 5 deg.C for min-1The temperature rise rate of (3) is to raise the temperature of the furnace from the temperature of the fourth stage to 490 ℃, and the temperature is kept for 12 hours. And then, furnace cooling is carried out to room temperature. Thus obtaining a two-step preparation of CoS2Coated FeS2Product (FeS)2@CoS2). The obtained core-shell sulfide composite was designated as (CP-2). And respectively taking the core-shell material and the iron disulfide as anode materials to prepare the single thermal battery. The diameter of the single battery is 17mm, the thickness of the single battery is 2mm, and the cathode of the single battery is Li-B. The current density is 200mA cm-2In the process, the effective discharge platform of the core-shell material is prolonged by 7.5 percent compared with the iron disulfide, and the current density is 200 mA-cm-2When the specific capacity is increased, the effective specific capacity is increased by 79mA h g-1The internal resistance was reduced by 11.1% (see fig. 8).
Example 7
Carrying out a vulcanization experiment on a precursor with high cobalt concentration;
the preparation process of the precursor is consistent with that of example 1, and the specific condition parameters are as follows:
the reaction temperature is set to be 75 ℃ in the experiment, and the concentration is taken to be 12 g.L-1CoSO of4170 ml and 20g of pretreated FeS2The powder is used as a raw material, and the pH value is respectively researched to be 11; stirring; then heating to 60-85 ℃ at the heating rate of 5 ℃/min in a water bath solution, stirring and preserving heat for a period of time; after the plating solution becomes clear; solid-liquid separation; and obtaining a precursor of the core-shell composite sulfide material. The phase analysis of the obtained electroless cobalt plating product is shown in CP-3(Co) in FIG. 5.
Adding simple substance sulfur powder into the prepared product, carrying out vulcanization reaction (enough sulfur powder), and carrying out a first stage at 10 ℃ for min-1Raising the temperature to 300 ℃ at the heating rate, and keeping the temperature for 7 hours; then entering the second stage at 5 deg.C for min-1The temperature of the furnace is raised from 300 ℃ to 350 ℃ at the temperature raising rate, and the temperature is kept for 15 h; the third stage, at 5 deg.C for min-1The temperature of the furnace is raised to 430 ℃ from the temperature of the second stage at the temperature raising rate of (1), and the temperature is kept for 15 hours. The fourth stage, at 5 deg.C for min-1The temperature rise rate of the furnace is to raise the temperature of the furnace from the third stage to 450 ℃ and keep the temperature for 15 hours. The fifth stage, at 5 deg.C for min-1The temperature rise rate of (3) is to raise the temperature of the furnace from the temperature of the fourth stage to 490 ℃, and the temperature is kept for 12 hours. The obtained core-shell sulfide composite was designated as (CP-3). And respectively taking the core-shell material and the iron disulfide as anode materials to prepare the single thermal battery. The diameter of the single battery is 17mm, the thickness of the single battery is 2mm, and the cathode of the single battery is Li-B. The current density is 200mA cm-2In time, the effective discharge platform of the core-shell type material is prolonged by 8.0 percent compared with iron disulfide, and the effective specific capacity is increased by 91mA h g-1The internal resistance was reduced by 11.3% (see fig. 8).
In the process of technical development, the chemical plating is also researched, then the vulcanization treatment is carried out, the vulcanization sintering is carried out at the vulcanization temperature of less than 350 ℃ under the condition of protective gas, but other Co and S composition phases (such as Co and S) are contained in the obtained coating3S4). While the performance of the thermal battery is improved after the thermal battery is assembledIs inferior to the present invention.