CN110233258B - Preparation method of modified lithium boron alloy composite negative electrode material for thermal battery - Google Patents
Preparation method of modified lithium boron alloy composite negative electrode material for thermal battery Download PDFInfo
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Abstract
The invention provides a modified lithium boron alloy composite negative electrode material for a thermal battery and a preparation method thereof, wherein the modified lithium boron alloy composite negative electrode material is prepared from Li7B6The lithium-magnesium solid solution phase and the ionic conducting agent phase, wherein the ionic conducting agent phase accounts for 1-15 wt% of the modified lithium-boron alloy composite negative electrode material; the modified lithium boron alloy is added with an ion conductive agent in advance, and the ion conductive agent is consistent with a conductive component in an electrolyte matched with a thermal battery. When the material is used as a negative electrode material for a thermal battery, the wettability of electrolyte and free lithium at the initial stage of low-temperature large-current discharge of the thermal battery is good, the electrode reaction rate can be increased, and the voltage peak dip can be improved. The method adopts a double-liquid mixing mode, can uniformly disperse the ionic conduction agent in the solid lithium boron alloy, has simple preparation process, and solves the problem that the ionic conduction agent and the lithium boron alloy cannot be mixed by a mechanical method in the later period.
Description
[ technical field ] A method for producing a semiconductor device
The invention belongs to the technical field of thermal batteries, and particularly relates to a preparation method of a modified lithium boron alloy composite negative electrode material for a thermal battery.
[ background of the invention ]
The thermal battery is a primary reserve battery activated by using molten salt as electrolyte and melting the molten salt by using a heat source. It has the features of high specific energy and power, wide temperature range, long storage period, fast and reliable activation, etc. and is one ideal power source for modern missile, gun and other weapons.
The lithium boron alloy is a novel thermal battery cathode material developed in recent years, and the structure of the lithium boron alloy is a dual-phase structure for adsorbing free Li in a heat-resistant porous skeleton lithium boron compound, so that the chemical property of the lithium boron alloy is close to that of pure Li, and the lithium boron alloy can keep the free Li not to overflow at 600 ℃ due to the adsorption effect of the lithium boron compound, thereby meeting the use requirement of the thermal battery at the temperature of about 500 ℃. The lithium boron alloy has the advantages of high specific capacity, good high-power performance and the like. However, in the initial stage of low-temperature large-current discharge of the lithium boron alloy thermal battery, because the internal temperature of the thermal battery is low, the electrolyte and the free lithium in the lithium boron alloy can not be completely infiltrated, part of the free lithium in the anode reaction can not be smoothly converted into lithium ions to enter the electrolyte, concentration polarization is generated, and a voltage concave peak is macroscopically shown, which can be solved only by adding a thermal design mode at present, and the mode can affect the safety of the battery and reduce the specific characteristics of the battery, so that the problem needs to be solved from the aspect of lithium boron alloy materials urgently.
[ summary of the invention ]
The invention aims to provide a preparation method of a modified lithium boron alloy composite negative electrode material for a thermal battery to overcome the defects of the prior art.
On one hand, the invention provides a modified lithium boron alloy composite negative electrode material for a thermal battery, which comprises the following components in percentage by weight:
Li7B6phase 41-69 wt%;
25-55 wt% of lithium-magnesium solid solution phase; and
1-15 wt% of ionic conductive agent phase.
Preferably, the composition is prepared from the following raw materials in percentage by weight:
preferably, the ion conductive agent has the same conductive component as the thermal battery electrolyte and is any one of LiCl-KCl binary salt, LiBr-LiCl-LiF ternary salt and binary or multi-element salt consisting of lithium salt of VII-group element and other inorganic salts of VII-group element in the periodic table,
the binary or multi-element salt composed of the VII-group element lithium salt and the VII-group element other inorganic salt in the periodic table can be preferably LiI-KI binary salt, LiBr-CsCl binary salt, LiBr-CsBr binary salt, LiCl-RbCl binary salt, LiBr-KBr-LiF ternary salt, CsBr-LiBr-KBr ternary salt, RbCl-LiCl-KCl ternary salt, LiBr-RbBr binary salt or LiCl-KCl2One of ternary salts.
On the other hand, the invention provides a preparation method of the modified lithium boron alloy composite negative electrode material for the thermal battery, which comprises the following steps:
s1, melting an ionic conduction agent to obtain a first melt;
s2, mixing the molten metal lithium, boron and metal magnesium to obtain a second melt;
s3, adding the first melt into the stirred second melt to obtain a mixed melt;
and S4, heating the mixed melt to react until a lithium boron compound skeleton is generated to obtain the solid alloy.
Preferably, the process is carried out in an inert gas atmosphere; the inert gas atmosphere has a water content of < 1ppm and an oxygen content of <10 ppm.
Preferably, the step S1 is performed at a temperature of 400-500 ℃, the step S2 is performed at a temperature of 250-400 ℃, and the stirring speed of the step S3 is not less than 1000 r/min.
Preferably, in the step S2, firstly, metal lithium is melted into lithium liquid, then boron and metal magnesium are added into the lithium liquid, the temperature of the lithium liquid is 250-.
Preferably, in the step S4, the temperature of the mixed melt is raised to 500-.
Preferably, after the solid alloy is obtained in step S4, the extrusion cogging and the rolling into a ribbon are continued.
On the other hand, the application also provides a thermal battery, and the negative electrode of the thermal battery is made of the modified lithium boron alloy composite negative electrode material.
The modified lithium boron alloy composite negative electrode material for the thermal battery is characterized in that an ion conductive agent is added in the modified lithium boron alloy in advance, and the ion conductive agent is consistent with conductive components in an electrolyte matched with the thermal battery, so that when the modified lithium boron alloy composite negative electrode material is used as the negative electrode material for the thermal battery, the wettability of the electrolyte and free lithium at the initial stage of low-temperature large-current discharge of the thermal battery is good, the electrode reaction rate can be improved, and the voltage concave peak can be improved. In the thermal battery discharge process, free lithium in the lithium boron alloy can transfer to the electrolyte and form the hole in the lithium boron alloy, and the electrolyte can fill in the lithium boron alloy hole, and when two kinds of materials wettability are poor, the electrolyte fills the hole slowly, can lead to the polarization to produce. The lithium boron alloy added with the ionic conductive agent in advance is easier to infiltrate and higher in filling efficiency because the alloy contains the same components, and the electrode reaction efficiency can be improved.
The preparation method of the modified lithium boron alloy composite negative electrode material provided by the invention adopts a double-liquid state mixing mode, can uniformly disperse the ionic conductive agent in the solid lithium boron alloy, has a simple preparation process, and solves the problem that the ionic conductive agent and the lithium boron alloy cannot be mixed by a mechanical method in the later stage.
[ description of the drawings ]
Fig. 1 is an X-ray diffraction phase diagram of the lithium boron alloy composite negative electrode material provided by the invention.
FIG. 2 is a schematic view of a reaction apparatus according to the present invention.
FIG. 3 is a comparative test chart of low-temperature 20A constant current discharge obtained by using the modified Li-B alloy obtained in example 1 as a battery negative plate.
FIG. 4 is a comparative test chart of low-temperature 20A constant current discharge obtained by using the modified Li-B alloy obtained in example 2 as a battery negative plate.
FIG. 5 is a low-temperature 13A constant-current discharge test chart of the modified Li-B alloy obtained in comparative example 3 as a battery negative plate.
[ detailed description ] embodiments
The invention is further described with reference to the following figures and embodiments.
The invention provides a modified lithium boron alloy composite negative electrode material for a thermal battery, which is prepared from Li7B6A phase, a lithium magnesium solid solution phase and an ion conductive agent phase, wherein Li7B6The phase accounts for 41-69 wt% of the modified lithium boron alloy composite negative electrode material, the lithium magnesium solid solution phase accounts for 25-55 wt% of the modified lithium boron alloy composite negative electrode material, the ionic conductive agent phase accounts for 1-15 wt% of the modified lithium boron alloy composite negative electrode material, the ionic conductive agent and the thermal battery electrolyte have the same conductive component, and the modified lithium boron alloy obtained according to the invention is a silver gray soft metal material.
Research shows that the electrical property of the alloy is not obviously improved when the ion conductive agent is added too little, the capacity of the alloy is lost when the ion conductive agent is added too much, and in addition, the alloy becomes brittle and the processing difficulty is increased. A certain amount of metal magnesium is added to form a lithium-magnesium solid solution phase with lithium, compared with pure lithium, the melting point is improved, the fluidity is reduced, and the high-temperature stability of the alloy is improved.
The modified lithium boron alloy composite negative electrode material is added with an ion conductive agent which is consistent with the conductive component in the electrolyte used in a matched manner in advance, when the modified lithium boron alloy composite negative electrode material is used as a negative electrode material for a thermal battery, the electrolyte and free lithium are well infiltrated in the initial stage of low-temperature large-current discharge of the thermal battery, the electrode reaction rate can be improved, and the voltage concave peak can be improved. The phase spectrum of the modified lithium boron alloy composite negative electrode material by X-ray diffraction is shown in figure 1. As can be seen from FIG. 1, the alloy is Li7B6The phase, the lithium magnesium phase and the ionic conductive agent are of a three-phase structure.
The modified lithium boron alloy composite negative electrode material for the thermal battery can be prepared from the following raw materials in percentage by weight: 52-68 wt% of metal lithium, 1-6 wt% of metal magnesium, 25-38 wt% of boron and 1-15 wt% of ion conductive agent. The lithium metal, magnesium metal and boron can be selected from chemical materials, wherein the purity of the preferred lithium metal is more than or equal to 99.9 percent, and the lithium metal can be lithium ingot or lithium particleA lithium band; the purity of the metal magnesium is more than or equal to 99 percent, and the state can be magnesium grains and magnesium powder; the purity of boron is more than or equal to 97 percent, and the boron is in a powder state. The ion conductive agent can be selected from LiCl-KCl binary salt, LiBr-LiCl-LiF ternary salt, or binary or polynary salt consisting of VII-group element lithium salt and VII-group element other inorganic salts in the periodic table, and can be particularly LiI-KI binary salt, LiBr-CsCl binary salt, LiBr-CsBr binary salt, LiCl-RbCl binary salt, LiBr-KBr-LiF ternary salt, CsBr-LiBr-KBr ternary salt, RbCl-LiCl-KCl ternary salt, LiBr-RbBr binary salt or LiCl-KCl-CaCl2One of ternary salts.
The preparation method of the modified lithium boron alloy composite negative electrode material for the thermal battery comprises the following steps:
s1, melting an ionic conduction agent to obtain a first melt;
s2, melting and mixing raw materials containing metal lithium, metal magnesium and boron to obtain a second melt;
s3, adding the first melt into the stirred second melt to obtain a mixed melt, wherein metal lithium accounts for 52-68 wt% of the mixed melt, metal magnesium accounts for 1-6 wt% of the mixed melt, boron powder accounts for 25-38 wt% of the mixed melt, and the ionic conductive agent accounts for 1-15 wt% of the mixed melt;
and S4, heating the mixed melt to react until a lithium boron compound skeleton is generated to obtain a solid alloy, wherein the solid alloy is a silver gray soft metal material.
In the preparation method, the ionic conducting agent as the first melt and the second melt containing molten metal lithium, metal magnesium and boron are mixed in a double-liquid mode in the smelting process, so that the uniform dispersion of the ionic conducting agent can be ensured. At normal temperature, the ionic conductive agent is powder, the lithium boron alloy is solid block, and the powder cannot be prepared, so that the lithium boron alloy is difficult to be uniformly mixed. The method adopts a double-liquid mode for mixing, and solves the problem that the ionic conductive agent and the lithium boron alloy cannot be mixed by a mechanical method in the later period. The mixing temperature can be further controlled, the phenomenon that the mixing effect is influenced by the fact that the ionic conductive agent is solidified into blocks when the temperature is too low is prevented, meanwhile, explosive reaction caused by too high temperature is prevented, meanwhile, the second melt is stirred strongly in the adding process of the ionic conductive agent, and the stirring speed is more than or equal to 1000 r/min. The optimized ion conductive agent of the first melt and the second melt containing molten metal lithium, metal magnesium and boron are subjected to the melt mixing steps of:
melting the ion conductive agent into a first melt for later use within the temperature range of 400-400 ℃, melting metal lithium into lithium liquid, adding boron and metal magnesium into the lithium liquid, wherein the temperature of the lithium liquid is 400 ℃ at the time of feeding, the boron needs to be fed in batches, the feeding weight does not exceed 10 wt% of the total weight of all raw materials each time, the feeding time interval is not less than 5min, after the uniform second melt is formed by adding, continuously raising the temperature of the second melt to 500 ℃ at the time of 400-500 ℃, and enabling the temperature difference between the second melt and the first melt to be within 10 ℃, and then mixing the two melts. The boron is added into the lithium solution to generate a contact reaction, the temperature of the solution is increased, if the local temperature is within 500 ℃, an explosive reaction is generally not initiated, for safety, the temperature rise of the solution is controlled to be as small as possible, preferably, the boron is added in batches, the generated heat can be rapidly dissipated, and if the boron is added in 5-8 batches, the temperature rise of the solution is within 20 ℃, so that the explosive reaction is not initiated.
At high temperature, the metallic lithium is easy to react with oxygen, nitrogen, water vapor and the like in the air, so the preparation method of the invention is preferably carried out in the inert gas atmosphere as a whole, prevents the metallic lithium from reacting with the oxygen and the water vapor, and reduces Li in the alloy2O, LiOH and the like, and further preferably an inert gas atmosphere having a water content of < 1ppm and an oxygen content of <10 ppm.
In the step S4, the temperature of the mixed melt is preferably raised to 500-550 ℃ at a temperature raising rate within the range of 1-5 ℃/min until the solid alloy is obtained by the reaction, and the temperature raising rate is limited to 1-5 ℃/min, so that the reaction can be ensured to be more sufficient, but the reaction cannot be too slow, and the efficiency is affected.
After the solid alloy is obtained, the solid alloy can be continuously extruded, cogging and rolled into a belt for later use after being cooled; the wafer for the negative electrode of the thermal battery can be further punched.
The preparation process of the present invention can be carried out in an apparatus as shown in FIG. 2. The preparation method can specifically adopt the following steps: in a glove box with oxygen content less than 0.1ppm and water content less than 10ppm, the ion conductive agent is put into a first iron crucible 1, the first iron crucible 1 is put into a tubular furnace 2 which can be inclined to rotate, the temperature is increased to 400-500 ℃ to melt the ion conductive agent, and the temperature of the melt is controlled to be the temperature for heat preservation, namely a first melt 3. Putting metal lithium into a second iron crucible 4, putting the second iron crucible 4 into a well-type resistance furnace 6, heating to 250-type 400 ℃ to melt the metal lithium, installing a stirring rod 5, carrying out strong stirring, adding boron powder and metal magnesium particles into lithium liquid, keeping the temperature at 250-type 400 ℃ and continuously stirring for more than 1h, then heating to 400-type 500 ℃ to ensure that the temperature difference between the second melt and the first melt is within 10 ℃, and controlling the temperature to keep the temperature, namely a second melt 7.
The first melt 3 in the first iron crucible 1 in the rotary tube furnace 2 is added into the second melt 7 which is stirred by strong force in the second iron crucible 4 in the well-type resistance furnace 6, and is stirred for more than 1h at the temperature of 400-500 ℃.
Stopping stirring, and raising the furnace temperature at the speed of 1-5 ℃/min until the liquid reacts to generate the solid alloy ingot.
The device has reasonable structural layout and can meet the preparation requirement of the invention.
Example 1
In a glove box having an oxygen content of <0.1ppm and a water content of 1.8ppm, 30g of a LiCl-KCl binary salt (wherein LiCl is 45 wt% and KCl is 55 wt%) as an ion conductive agent was placed in a first iron crucible, the iron crucible was placed in a tiltable rotary tube furnace, the temperature was raised to 420 ℃ to melt the ion conductive agent, and the melt temperature was controlled at this temperature and held, which was a first melt. 659.6g of metal lithium is placed into a second iron crucible, the iron crucible is placed into a well-type resistance furnace, the temperature is raised to 250 ℃ to melt the metal lithium, a stirring rod is installed to carry out strong stirring, the stirring speed is 1000r/min, 252.2g of boron powder is divided into 5 parts according to the weight average, one part is added into the lithium liquid at intervals of 10min until the addition is finished, 58.2g of metal magnesium particles are added into the lithium liquid at intervals of 10min at one time, the temperature is kept at 250 ℃ +/-10 ℃ and stirred for 2h, then the temperature is raised to 420 ℃ and the temperature is controlled to be kept, and the second melt is obtained.
The first melt in the first crucible in the rotary tube furnace was added to the vigorously stirred second melt in the second crucible in the well-type resistance furnace and stirred for 2h while being maintained at 420 ℃. + -. 5 ℃.
Stopping stirring, raising the furnace temperature to 520 ℃ at the speed of 3 ℃/min, and carrying out liquid reaction to generate a solid alloy ingot. Obtaining Li by theoretical calculation under the condition of complete reaction7B6The phase accounts for 44.92 wt% of the modified lithium boron alloy composite negative electrode material, the lithium magnesium solid solution phase accounts for 52.08 wt% of the modified lithium boron alloy composite negative electrode material, and the ionic conductive agent phase accounts for 3 wt% of the modified lithium boron alloy composite negative electrode material.
And taking the cooled alloy ingot out of the crucible in a drying room with the dew point of-43 ℃, removing surface oxide skin by using a grinding wheel machine, extruding the alloy ingot into a 5mm strip by using a profile extruder, rolling the strip into a 0.6mm thin strip by using a double-roll film rolling machine (the pressing proportion is less than 20 percent each time), and then punching the thin strip into a wafer with the diameter of 58mm by using a punching machine.
A thermal battery is assembled by taking a conventional lithium boron alloy sheet and a modified lithium boron alloy sheet as negative electrodes, cobalt disulfide as a positive electrode (excessive positive electrode) and LiCl-KCl-MgO as electrolytes, standing for 6 hours in a low-temperature box at-40 ℃, then taking out and carrying out a 20A constant-current discharge comparative test, and the test result is shown in figure 3, and it can be known from figure 3 that the voltage concave peak at the early stage of the modified lithium boron alloy sheet obtained by the embodiment is obviously improved (the voltage sudden drop in the figure is caused by pulse current) compared with the conventional lithium boron alloy sheet.
Example 2
In a glove box with oxygen content less than 0.1ppm and water content of 1.0ppm, 90g of LiBr-LiCl-LiF ternary salt (wherein LiBr is 68 wt%, LiCl is 22 wt% and LiF is 10 wt%) as an ion conductive agent is put into a first iron crucible, the iron crucible is put into a tubular furnace which can be tilted to rotate, the temperature is increased to 480 ℃ to melt the ion conductive agent, and the temperature of the melt is controlled to be the temperature for heat preservation, so that the first melt is obtained. 546g of metal lithium is placed into a second iron crucible, the iron crucible is placed into a well-type resistance furnace, the temperature is increased to 300 ℃ to melt the metal lithium, a stirring rod is installed to carry out strong stirring, the stirring speed is 1000r/min, 327.6g of boron powder is evenly divided into 6 parts by weight, one part is added into the lithium liquid at intervals of 10min until the addition is finished, 36.4g of metal magnesium particles are added into the lithium liquid at intervals of 10min at one time, the temperature is kept at 300 +/-10 ℃ and stirred for 3h, then the temperature is increased to 480 ℃ and the temperature is controlled to be kept, and the second melt is obtained.
The first melt in the first crucible in the rotary tube furnace is added to the strongly stirred second melt in the second crucible in the well resistance furnace.
Stopping stirring, raising the furnace temperature to 520 ℃ at the speed of 2 ℃/min, and carrying out liquid reaction to generate a solid alloy ingot. Li obtained by theoretical calculation under complete reaction condition7B6The phase accounts for 57.3 wt% of the modified lithium boron alloy composite negative electrode material, the lithium magnesium solid solution phase accounts for 33.7 wt% of the modified lithium boron alloy composite negative electrode material, and the ionic conductive agent phase accounts for 9 wt% of the modified lithium boron alloy composite negative electrode material.
In order to verify the three-phase distribution uniformity of the lithium boron phase, the lithium magnesium phase and the ion conductive agent in the alloy, 5 samples are taken at different positions of the alloy to test the lithium and magnesium contents, an inductively coupled plasma atomic emission spectrometer (ICP-AES) is adopted for the test, the test results are shown in Table 1, and as the theoretical lithium content of the lithium boron phase in the alloy is 39.1 wt%, the theoretical lithium content in the lithium magnesium solid solution is 80-90 wt%, the theoretical lithium content of the ion conductive agent phase is less than 12 wt%, and the lithium content difference of each phase structure is large, the data in Table 1 shows that the lithium content and the magnesium content of 5 groups of samples are good in consistency, so that the uniform dispersion of each phase in the alloy can be estimated.
TABLE 1 lithium and magnesium content of the samples
| Sample numbering | Lithium content% | Content of magnesium% |
| 1# | 56.02 | 3.72 |
| 2# | 56.10 | 3.70 |
| 3# | 55.93 | 3.71 |
| 4# | 56.02 | 3.71 |
| 5# | 55.99 | 3.71 |
| Standard deviation of | 0.061 | 0.007 |
And taking the cooled alloy ingot out of the crucible in a drying room with the dew point of-45 ℃, removing surface oxide skin by using a grinding wheel machine, extruding the alloy ingot into a 5mm strip by using a profile extruder, rolling the strip into a 0.6mm thin strip by using a double-roll film rolling machine (the pressing proportion is less than 20 percent each time), and then punching the thin strip into a wafer with the diameter of 58mm by using a punching machine.
A thermal battery is assembled by taking a conventional lithium boron alloy sheet and a modified lithium boron alloy sheet as negative electrodes, cobalt disulfide as a positive electrode (excessive positive electrode) and LiBr-LiCl-LiF + MgO as electrolytes, standing for 6 hours in a low-temperature box at-40 ℃, then taking out and carrying out a 20A constant-current discharge comparative test, and the test result is shown in figure 4, and it can be known from figure 4 that the voltage concave peak at the early stage of the modified lithium boron alloy sheet obtained by the embodiment is obviously improved (the voltage sudden drop is caused by pulse current in the figure) compared with the conventional lithium boron alloy sheet.
Example 3
In a glove box having an oxygen content of <0.1ppm and a water content of 1.8ppm, 55g of a LiCl-KCl binary salt (wherein LiCl is 45 wt% and KCl is 55 wt%) as an ion conductive agent was placed in a first iron crucible, the iron crucible was placed in a tiltable rotary tube furnace, the temperature was raised to 450 ℃ to melt the ion conductive agent, and the melt temperature was controlled at this temperature and held, which was a first melt. Placing 600g of metal lithium into a second iron crucible, placing the iron crucible into a well-type resistance furnace, heating to 350 ℃ to melt the metal lithium, installing a stirring rod, carrying out strong stirring at a stirring speed of 1000r/min, equally dividing 310g of boron powder into 5 parts by weight, adding one part into lithium liquid at intervals of 8min until the addition is finished, adding 35g of metal magnesium particles into the lithium liquid at intervals of 8min, keeping the temperature at 350 +/-10 ℃ and stirring for 2h, heating to 450 ℃ and keeping the temperature at the temperature, thus obtaining a second melt.
The first melt in the first crucible in the rotary tube furnace was added to the vigorously stirred second melt in the second crucible in the well resistance furnace and stirred for 2h while being maintained at 450 ℃. + -. 5 ℃.
Stopping stirring, raising the furnace temperature to 540 ℃ at the speed of 4 ℃/min, and carrying out liquid reaction to generate a solid alloy ingot. Li obtained by theoretical calculation under complete reaction condition7B6The phase accounts for 54.22 wt% of the modified lithium boron alloy composite negative electrode material, the lithium magnesium solid solution phase accounts for 40.28 wt% of the modified lithium boron alloy composite negative electrode material, and the ionic conductive agent phase accounts for 5.5 wt% of the modified lithium boron alloy composite negative electrode material.
Example 4
In a glove box having an oxygen content of <0.1ppm and a water content of 1.8ppm, 20g of a LiCl-KCl binary salt (wherein LiCl is 45 wt% and KCl is 55 wt%) as an ion conductive agent was placed in a first iron crucible, the iron crucible was placed in a tiltable rotary tube furnace, the temperature was raised to 480 ℃ to melt the ion conductive agent, and the melt temperature was controlled at this temperature and held, which was a first melt. Putting 555g of metal lithium into a second iron crucible, putting the iron crucible into a well-type resistance furnace, heating to 330 ℃ to melt the metal lithium, installing a stirring rod, carrying out strong stirring at a stirring speed of 1000r/min, equally dividing 370g of boron powder into 5 parts by weight, adding one part into the lithium liquid at intervals of 8min until the addition is finished, adding 55g of metal magnesium particles into the lithium liquid at intervals of 8min, keeping the temperature at 330 +/-10 ℃ and stirring for 2h, heating to 480 ℃ and keeping the temperature at the temperature, thus obtaining a second melt.
The first melt in the first crucible in the rotary tube furnace was added to the vigorously stirred second melt in the second crucible in the well resistance furnace and stirred for 2h while being maintained at 480 ℃. + -. 5 ℃.
Stopping stirring, raising the furnace temperature to 530 ℃ at the speed of 3 ℃/min, and carrying out liquid reaction to generate a solid alloy ingot. Li obtained by theoretical calculation under complete reaction condition7B6The phase accounts for 64.72 wt% of the modified lithium boron alloy composite negative electrode material, the lithium magnesium solid solution phase accounts for 33.28 wt% of the modified lithium boron alloy composite negative electrode material, and the ionic conductive agent phase accounts for 2 wt% of the modified lithium boron alloy composite negative electrode material.
Example 5
In a glove box with oxygen content less than 0.1ppm and water content of 1.8ppm, 15g of LiBr-KBr-LiF ternary salt (wherein LiBr is 57.3 wt%, KBr is 42 wt% and LiF is 0.7 wt%) as an ion conductive agent is put into a first iron crucible, the iron crucible is put into a tubular furnace which can be inclined to rotate, the temperature is increased to 450 ℃ to melt the ion conductive agent, and the temperature of the melt is controlled to be kept at the temperature, so that the first melt is obtained. 560g of metallic lithium is placed into a second iron crucible, the iron crucible is placed into a well-type resistance furnace, the temperature is raised to 280 ℃ to melt the metallic lithium, a stirring rod is arranged to carry out strong stirring, the stirring speed is 1000r/min, 370g of boron powder is divided into 5 parts according to weight average, one part is added into lithium liquid at intervals of 8min until the addition is finished, 55g of metallic magnesium particles are added into the lithium liquid at intervals of 8min at one time, the temperature is kept at 280 +/-10 ℃ and stirred for 2h, then the temperature is raised to 450 ℃ and the temperature is controlled to be kept, and the second melt is obtained.
The first melt in the first crucible in the rotary tube furnace was added to the vigorously stirred second melt in the second crucible in the well resistance furnace and stirred for 2h while being maintained at 450 ℃. + -. 5 ℃.
Stopping stirring, raising the furnace temperature to 530 ℃ at the speed of 3 ℃/min, and carrying out liquid reaction to generate a solid alloy ingot. Conditions for reaction completionLi obtained by theoretical calculation7B6The phase accounts for 64.72 wt% of the modified lithium boron alloy composite negative electrode material, the lithium magnesium solid solution phase accounts for 33.78 wt% of the modified lithium boron alloy composite negative electrode material, and the ionic conductive agent phase accounts for 1.5 wt% of the modified lithium boron alloy composite negative electrode material.
Comparative example 1
In a glove box with oxygen content less than 0.1ppm and water content of 1.0ppm, 60g of LiBr-LiCl-LiF ternary salt (wherein LiBr is 68 wt%, LiCl is 22 wt% and LiF is 10 wt%) as an ion conductive agent is put into a first iron crucible, the iron crucible is put into a tubular furnace which can be tilted to rotate, the temperature is increased to 460 ℃ to melt the ion conductive agent, and the temperature of the melt is controlled to be the temperature for heat preservation, so that the first melt is obtained. 500g of metal lithium is placed into a second iron crucible, the iron crucible is placed into a well-type resistance furnace, the temperature is increased to 300 ℃ to melt the metal lithium, a stirring rod is installed to carry out strong stirring, the stirring speed is 1200r/min, 400g of boron powder is divided into 8 parts according to weight, one part is added into lithium liquid at intervals of 10min until the addition is finished, 40g of metal magnesium particles are added into the lithium liquid at intervals of 10min at one time, the temperature is kept at 300 +/-10 ℃ and stirred for 4h, then the temperature is increased to 460 ℃, the temperature is controlled to be kept, and the second melt is obtained.
The first melt in the first crucible in the rotary tube furnace is added to the strongly stirred second melt in the second crucible in the well resistance furnace.
Stopping stirring, and raising the furnace temperature to 520 ℃ at the speed of 2 ℃/min to enable the liquid to react to generate a solid alloy ingot. Li obtained by theoretical calculation under complete reaction condition7B6The phase accounts for 76.6 percent of the modified lithium boron alloy composite negative electrode material, the lithium magnesium solid solution phase accounts for 17.4 percent of the modified lithium boron alloy composite negative electrode material, and the ionic conductive agent phase accounts for 6 percent of the modified lithium boron alloy composite negative electrode material.
The cooled alloy ingot is taken out of a crucible in a drying room with the dew point of-45 ℃, surface oxide skin is removed by a grinding wheel machine, a 5mm strip is extruded by a profile extruder, a 0.6mm thin strip is rolled by a double-roll film rolling machine (the pressing proportion is less than 20% each time), black spots are visible on the surface of the alloy, the black spots are dissolved by deionized water, and insoluble black particles are still remained after the aqua regia is acidified, so that boron powder which is not completely reacted is contained in the alloy.
Comparative example 2
In a glove box with oxygen content less than 0.1ppm and water content of 1.1ppm, 160g of LiBr-LiCl-LiF ternary salt (wherein LiBr is 68 wt%, LiCl is 22 wt% and LiF is 10 wt%) as an ion conductive agent is put into a first iron crucible, the iron crucible is put into a tubular furnace which can be tilted to rotate, the temperature is increased to 460 ℃ to melt the ion conductive agent, and the temperature of the melt is controlled to be the temperature for heat preservation, so that the first melt is obtained. 563.2g of metal lithium is placed into a second iron crucible, the iron crucible is placed into a well-type resistance furnace, the temperature is raised to 300 ℃ to melt the metal lithium, a stirring rod is installed to carry out strong stirring, the stirring speed is 1200r/min, 256.8g of boron powder is divided into 6 parts according to the weight on average, one part is added into the lithium liquid at an interval of 10min until the addition is finished, 20g of metal magnesium particles are added into the lithium liquid at one time at an interval of 10min, the temperature is kept at 300 +/-10 ℃ and stirred for 4h, then the temperature is raised to 460 ℃ and the temperature is controlled to be kept, and the second melt is obtained.
The first melt in the first crucible in the rotary tube furnace is added to the strongly stirred second melt in the second crucible in the well resistance furnace.
Stopping stirring, raising the furnace temperature to 520 ℃ at the speed of 2 ℃/min, and carrying out liquid reaction to generate a solid alloy ingot. Li obtained by theoretical calculation under complete reaction condition7B6The phase accounts for 44.92% of the modified lithium boron alloy composite negative electrode material, the lithium magnesium solid solution phase accounts for 39.08 wt% of the modified lithium boron alloy composite negative electrode material, and the ionic conductive agent phase accounts for 16 wt% of the modified lithium boron alloy composite negative electrode material.
And taking the cooled alloy ingot out of the crucible in a drying room with the dew point of-45 ℃, removing surface oxide skin by using a grinding wheel machine, extruding the alloy ingot into a 5mm strip by using a profile extruder, rolling the strip into a 0.6mm thin strip by using a double-roll film rolling machine (the pressing proportion is less than 20 percent each time), cracking, layering and the like of the alloy strip, wherein the alloy strip cannot be assembled into a battery for use, and the reason is that the ductility of the alloy is insufficient due to excessive addition of an ionic conductive agent through analysis.
Comparative example 3
In a glove box with oxygen content less than 0.1ppm and water content of 1.0ppm, 60g of LiBr-LiCl-LiF ternary salt (wherein LiBr is 68 wt%, LiCl is 22 wt% and LiF is 10 wt%) as an ion conductive agent is put into a first iron crucible, the iron crucible is put into a tubular furnace which can be tilted to rotate, the temperature is increased to 460 ℃ to melt the ion conductive agent, and the temperature of the melt is controlled to be the temperature for heat preservation, so that the first melt is obtained. 700g of metal lithium is placed into a second iron crucible, the iron crucible is placed into a well-type resistance furnace, the temperature is raised to 380 ℃ to melt the metal lithium, a stirring rod is arranged to carry out strong stirring, the stirring speed is 1000r/min, 220g of boron powder is divided into 4 parts according to weight average, one part is added into lithium liquid at intervals of 10min until the addition is finished, 20g of metal magnesium particles are added into the lithium liquid at intervals of 10min at one time, the temperature is kept at 380 +/-10 ℃ and stirred for 1.5h, then the temperature is raised to 460 ℃ and the temperature is controlled to be kept, and the second melt is obtained.
The first melt in the first crucible in the rotary tube furnace is added to the strongly stirred second melt in the second crucible in the well resistance furnace.
Stopping stirring, raising the furnace temperature to 520 ℃ at the speed of 5 ℃/min, and carrying out liquid reaction to generate a solid alloy ingot. Li by theoretical calculation7B6The phase accounts for 38.48 wt% of the modified lithium boron alloy composite negative electrode material, the lithium magnesium solid solution phase accounts for 55.52 wt% of the modified lithium boron alloy composite negative electrode material, and the ionic conductive agent phase accounts for 6 wt% of the modified lithium boron alloy composite negative electrode material.
And taking the cooled alloy ingot out of the crucible in a drying room with the dew point of-43 ℃, removing surface oxide skin by using a grinding wheel machine, extruding the alloy ingot into a 5mm strip by using a profile extruder, rolling the strip into a 0.6mm thin strip by using a double-roll film rolling machine (the pressing proportion is less than 20 percent each time), and then punching the thin strip into a wafer with the diameter of 58mm by using a punching machine.
The lithium boron alloy sheet is used as a negative electrode, cobalt disulfide is used as a positive electrode (the positive electrode is excessive), LiBr-LiCl-LiF + MgO is used as electrolyte to assemble a thermal battery, the thermal battery is placed in a low-temperature box at minus 40 ℃ for 6 hours and then taken out to perform 13A constant current discharge, the test result is shown in figure 5, as can be seen from figure 5, the modified lithium boron alloy sheet obtained by the embodiment has instantaneous drop of a plurality of voltages in the discharge period, which indicates that the short circuit occurs locally in the battery, and through the anatomical analysis of the battery, the side edge of the battery has negative electrode overflow, the reason of the short circuit is analyzed, namely the lithium content of the lithium boron alloy is too high, the lithium magnesium solid solution cannot be completely adsorbed in the lithium boron alloy framework with less relative content, and the overflow occurs under the discharge environment with high temperature and high.
While the foregoing is directed to embodiments of the present invention, it will be understood by those skilled in the art that various changes may be made without departing from the spirit and scope of the invention.
Claims (7)
1. The preparation method of the modified lithium boron alloy composite negative electrode material for the thermal battery is characterized in that the modified lithium boron alloy composite negative electrode material comprises the following components in percentage by weight:
Li7B6phase 41-69 wt%;
25-55 wt% of lithium-magnesium solid solution phase; and
1-15 wt% of ionic conductive agent phase;
the ion conductive agent is selected from LiCl-KCl binary salt, LiBr-LiCl-LiF ternary salt, LiI-KI binary salt, LiBr-CsCl binary salt, LiBr-CsBr binary salt, LiCl-RbCl binary salt, LiBr-KBr-LiF ternary salt, CsBr-LiBr-KBr ternary salt, RbCl-LiCl-KCl ternary salt, LiBr-RbBr binary salt or LiCl-KCl2One of ternary salts;
the preparation method comprises the following steps:
s1, melting an ionic conduction agent to obtain a first melt;
s2, mixing the molten metal lithium, boron and metal magnesium to obtain a second melt;
s3, adding the first melt into the stirred second melt to obtain a mixed melt;
and S4, heating the mixed melt for reaction until a lithium boron compound skeleton is generated to obtain the solid alloy.
2. The method for preparing the modified lithium boron alloy composite negative electrode material for the thermal battery according to claim 1, wherein the modified lithium boron alloy composite negative electrode material is prepared from the following raw materials in percentage by weight:
3. the method for preparing a modified lithium boron alloy composite negative electrode material for a thermal battery according to claim 1,
the process is carried out in an inert gas atmosphere; the inert gas atmosphere has a water content of < 1ppm and an oxygen content of <10 ppm.
4. The method for preparing a modified lithium boron alloy composite negative electrode material for a thermal battery according to claim 1,
the step S1 is carried out in the temperature range of 400-500 ℃, the step S2 is carried out in the temperature range of 250-400 ℃, and the stirring speed of the step S3 is more than or equal to 1000 r/min.
5. The method for preparing a modified lithium boron alloy composite negative electrode material for a thermal battery according to claim 4,
step S2, firstly melting lithium metal into lithium liquid, then adding boron and magnesium metal into the lithium liquid, wherein the temperature of the lithium liquid is 250-fold-400 ℃ during feeding, the boron needs to be fed in batches, the feeding weight does not exceed 10 wt% of the total weight of all raw materials each time, the feeding time interval is not less than 5min, after the uniform second melt is formed by adding, the temperature of the second melt is continuously raised to 400-fold-500 ℃, so that the temperature difference between the second melt and the first melt is within 10 ℃, and then the two melts can be mixed.
6. The method for preparing a modified lithium boron alloy composite negative electrode material for a thermal battery according to claim 1,
step S4, heating the mixed melt to 500-550 ℃ at a heating rate within the range of 1-5 ℃/min until the solid alloy is obtained by reaction, and ending the smelting process.
7. A thermal battery, characterized by: the negative electrode is made of the modified lithium boron alloy composite negative electrode material prepared by the preparation method of any one of claims 1 to 6.
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