Electrolyte of high-capacity lithium thionyl chloride battery and preparation method of electrolyte

Abstract

The invention provides an electrolyte of a high-capacity lithium thionyl chloride battery and a preparation method of the electrolyte. The method comprises the following steps: step 1, preparing raw materials; respectively purifying thionyl chloride and carbon tetrachloride, and drying lithium aluminum tetrachloride and sulfur dioxide; step 2, under a dry condition, adding lithium tetrachloroaluminate into thionyl chloride, and stirring to prepare a premix; step 3, putting a lithium sheet into the premix, heating and refluxing at 60-70 DEG C until the lithium sheet becomes black, filtering, and continuously repeating the operation until the lithium sheet does not obviously become black; and 4, adding carbon tetrachloride into the premix subjected to impurity removal, and introducing sulfur dioxide gas to prepare the electrolyte. According to the preparation method of the electrolyte, the raw materials are easy to obtain, the process is simple, the requirement of industrial production is met, meanwhile, the carbon tetrachloride additive can partially dissolve sulfur generated in the discharging process, more reaction active sites are exposed, the phenomenon of passivation and inactivation of a carbon positive electrode can be effectively relieved, and therefore the capacity of a lithium thionyl chloride battery is improved.

Description

Technical Field

[0001] The invention relates to the technical field of lithium thionyl chloride batteries, and in particular to an electrolyte of a high-capacity lithium thionyl chloride battery and a preparation method thereof. Background Art

[0002] Lithium thionyl chloride battery is a primary chemical power source composed of negative electrode metal lithium, carbon positive electrode and non-aqueous electrolyte (lithium tetrachloroaluminate-thionyl chloride). Thionyl chloride is both electrolyte solvent and positive electrode reaction active substance. Its high boiling point and low freezing point ensure a wide operating temperature range of the battery. Carbon is an inert positive electrode and does not participate in chemical reactions, but can provide a place for electrochemical reactions. The metal lithium negative electrode has the advantages of high capacity and low potential, which ensures the high energy density of the battery. In addition, after contacting with the electrolyte, the metal lithium spontaneously reacts to form a lithium chloride film that coats the surface of the lithium negative electrode, which can act as a physical barrier to prevent further contact between lithium and the electrolyte, avoid side reactions, and ensure a longer storage time of the battery.

[0003] The overall reaction of lithium thionyl chloride battery is 4Li+2SOCl2→4LiCl+S+SO2. A small part of the sulfur generated during the discharge process dissolves in the electrolyte, and most of it is deposited on the carbon surface or in the pores, which hinders the further contact between the electrode and the electrolyte, causing the carbon positive electrode to gradually passivate or even deactivate, resulting in a decrease in battery capacity. The common method to solve this problem before was to regulate the pore structure of the carbon positive electrode. Patent CN104518218A prepared a series of hierarchical porous carbons by template method. This method is costly and cumbersome to operate, involving carbonization, acid etching and other processes; CN 109449372 A patent coats acetylene black slurry on metal wire and then weaves it into a mesh with activated carbon fiber to make a porous positive electrode. This method is also more complicated to operate. It can be seen that optimizing the positive electrode structure is one of the strategies to solve the above problems, but it is difficult to be consistent with actual production.

[0004] Therefore, it is urgent to develop a new method to solve the problem of sulfur passivation of the positive electrode. Summary of the invention

[0005] In view of this, the present invention provides an electrolyte for a high-capacity lithium thionyl chloride battery and a preparation method thereof, which simply and effectively alleviates the phenomenon of sulfur passivation of the carbon positive electrode by adding a carbon tetrachloride additive, thereby improving the capacity and service life of the lithium thionyl chloride battery.

[0006] In a first aspect, the present invention provides a method for preparing an electrolyte for a high-capacity lithium thionyl chloride battery, the method comprising the following steps:

[0007] Step 1: Raw material pretreatment

[0008] preparing constituent raw materials; purifying thionyl chloride and carbon tetrachloride respectively, and drying lithium tetrachloroaluminate and sulfur dioxide;

[0009] Step 2: Premix

[0010] Under dry conditions, adding the lithium tetrachloroaluminate pretreated in step 1 to thionyl chloride, stirring, to prepare a premix;

[0011] Step 3: Remove impurities

[0012] Place the lithium sheet in the premix of step 2, heat and reflux at 60-70°C until the lithium sheet turns black, filter, take another lithium sheet and place it in the filtered premix, and continue to reflux for 1 hour. If the lithium sheet does not turn black, the impurity removal is completed; if the lithium sheet turns black, continue to repeat the above operation until the lithium sheet is not obviously black;

[0013] Step 4: Prepare electrolyte

[0014] The carbon tetrachloride pretreated in step one is added to the premix after impurities are removed in step three, and sulfur dioxide gas is introduced to obtain an electrolyte.

[0015] On the basis of the above technical solution, preferably, in step 1, the purifying of thionyl chloride and carbon tetrachloride respectively comprises:

[0016] Thionyl chloride and carbon tetrachloride were purified separately by distillation in a fume hood.

[0017] On the basis of the above technical solution, preferably, in step 1, the drying of lithium tetrachloroaluminate comprises:

[0018] Lithium tetrachloroaluminate was vacuum dried at 60°C for 12 h, and then replaced with dry argon three times and vacuum dried at 60°C for another 12 h.

[0019] On the basis of the above technical solution, preferably, in step 1, the drying of sulfur dioxide comprises: passing sulfur dioxide into a gas washing bottle filled with molecular sieves.

[0020] On the basis of the above technical solution, preferably, the molecular sieve is a 3A type molecular sieve.

[0021] On the basis of the above technical solution, preferably, in step 2, the concentration of lithium tetrachloroaluminate in the premix is ​​1 mol / L.

[0022] In a second aspect, the present invention relates to an electrolyte for a high-capacity lithium thionyl chloride battery prepared by the above method, comprising thionyl chloride and lithium tetrachloroaluminate.

[0023] On the basis of the above technical solution, preferably, carbon tetrachloride is further included, and the carbon tetrachloride accounts for 5-10% of the total mass of the thionyl chloride and the lithium tetrachloroaluminate.

[0024] On the basis of the above technical solution, preferably, sulfur dioxide is further included, and the sulfur dioxide accounts for 5% of the total mass of the thionyl chloride and the lithium tetrachloroaluminate.

[0025] The electrolyte of the high-capacity lithium thionyl chloride battery and the preparation method thereof provided by the present invention have the following beneficial effects compared with the prior art:

[0026] The preparation method of the lithium thionyl chloride battery electrolyte provided by the invention has readily available raw materials, a simple process, and meets the requirements of industrial production. Meanwhile, the carbon tetrachloride additive can partially dissolve the sulfur generated during the discharge process, exposing more reactive sites, and can effectively alleviate the passivation and deactivation phenomenon of the carbon positive electrode, thereby improving the capacity of the lithium thionyl chloride battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0028] Figure 1 330Ω constant resistance discharge curves of lithium thionyl chloride batteries prepared in Examples 1, 2, 3 and Comparative Examples 1, 2, 3 at room temperature.

[0029] Figure 2 1000Ω constant resistance discharge curves of lithium thionyl chloride batteries prepared in Examples 1, 2, 3 and Comparative Examples 1, 2, 3 at room temperature. DETAILED DESCRIPTION

[0030] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0031] Example 1

[0032] Thionyl chloride and carbon tetrachloride were purified separately by distillation in a fume hood. For thionyl chloride, the components distilled at about 68°C were mainly collected; for carbon tetrachloride, the components distilled at about 76°C were mainly collected.

[0033] Lithium tetrachloroaluminate was placed in a vacuum drying oven and vacuum dried at 60°C for 12 hours, then replaced with dry argon gas three times and vacuum dried at 60°C for another 12 hours.

[0034] Under dry conditions, slowly pour 178 g of dry lithium tetrachloroaluminate into about 500 mL of thionyl chloride, mix and stir to avoid rapid heat release and explosive boiling of the electrolyte, and finally pour into a 1 L volumetric flask to make a solution with a lithium tetrachloroaluminate concentration of 1 mol / L.

[0035] Put about 50g of bright lithium strip into the solution prepared in the previous step, heat and reflux at 60-70℃ for 10h to fully remove impurities in the electrolyte. It is normal for the lithium sheet to turn black after reflux. Then filter it in a glove box or drying room. Then continue to add new lithium sheets to the filtered solution, reflux for one hour. If the lithium sheet does not turn black, it means that the impurities have been removed, and finally filter it.

[0036] 88 g of sulfur dioxide gas that has been dehydrated by 3A molecular sieve was introduced into the above filtrate and allowed to stand for 1 hour.

[0037] Add 84 g of carbon tetrachloride (5% of the mass of lithium tetrachloroaluminate and thionyl chloride) to the above solution to obtain the desired electrolyte.

[0038] An energy-type lithium thionyl chloride battery is made according to the ER14250 battery process, wherein acetylene black particles are used as the positive electrode, metallic lithium is used as the negative electrode, and the solution prepared by the above method is used as the electrolyte.

[0039] The ER14250 lithium thionyl chloride battery in this example was subjected to 330Ω and 1000Ω constant resistance discharge at room temperature. The results are as follows: Figure 1 and 2 shown.

[0040] Example 2

[0041] The difference between this embodiment and embodiment 1 is that the mass of carbon tetrachloride added is 135 g (8% of the mass of lithium tetrachloroaluminate and thionyl chloride), and the other conditions and parameters are exactly the same as those in embodiment 1.

[0042] The ER14250 lithium thionyl chloride battery in this example was subjected to 330Ω and 1000Ω constant resistance discharge at room temperature. The results are as follows: Figure 1 and 2 shown.

[0043] Example 3

[0044] The difference between this embodiment and embodiment 1 is that the mass of carbon tetrachloride added is 168 g (10% of the mass of lithium tetrachloroaluminate and thionyl chloride), and the other conditions and parameters are exactly the same as those in embodiment 1.

[0045] The ER14250 lithium thionyl chloride battery in this example was subjected to 330Ω and 1000Ω constant resistance discharge at room temperature. The results are as follows: Figure 1 and 2 shown.

[0046] Comparative Example 1

[0047] The difference between this comparative example and Example 1 is that carbon tetrachloride is omitted, and the remaining conditions and parameters are exactly the same as those in the example.

[0048] The ER14250 lithium thionyl chloride battery configured in this comparative example was subjected to 330Ω and 1000Ω constant resistance discharge at room temperature. The results are as follows Figure 1 and 2 shown.

[0049] Depend on Figure 1 , 2 It can be seen that the battery prepared in this comparative example has a 330Ω constant group discharge time of 113.9 hours at room temperature; and a 1000Ω constant group discharge time of 300.9 hours, and the discharge effect is poor.

[0050] Comparative Example 2

[0051] The difference between this comparative example and Example 1 is that the mass of carbon tetrachloride added is 34 g (2% of the mass of lithium tetrachloroaluminate and thionyl chloride), and the other conditions and parameters are exactly the same as those in Example 1.

[0052] The ER14250 lithium thionyl chloride battery configured in this comparative example was subjected to 330Ω and 1000Ω constant resistance discharge at room temperature. The results are as follows Figure 1 and 2 shown.

[0053] Depend on Figure 1 , 2 It can be seen that the battery prepared in this comparative example has a 330Ω constant group discharge time of 114.1h at room temperature; and a 1000Ω constant group discharge time of 302.6h, which is close to the discharge time of comparative example 1, and the discharge effect is poor.

[0054] Comparative Example 3

[0055] The difference between this comparative example and Example 1 is that the mass of carbon tetrachloride added is 252 g (15% of the mass of lithium tetrachloroaluminate and thionyl chloride), and the other conditions and parameters are exactly the same as those in Example 1.

[0056] The ER14250 lithium thionyl chloride battery configured in this comparative example was subjected to 330Ω and 1000Ω constant resistance discharge at room temperature. The results are as follows Figure 1 and 2 shown.

[0057] Depend on Figure 1 , 2 It can be seen that the battery prepared in this comparative example has a 330Ω constant group discharge time of 106.6h at room temperature, which is 6.5% shorter than that of comparative example 1; the 1000Ω constant group discharge time is 280.8h, which is 6.7% shorter than that of comparative example 1, and the discharge effect is poor. This is because although carbon tetrachloride can dissolve part of the sulfur generated during the discharge process and effectively alleviate the passivation of the positive electrode, excessive addition will lead to a decrease in the content of thionyl chloride, an active substance in the electrolyte, and reduce the battery capacity.

[0058] An energy-type lithium thionyl chloride battery was made according to the ER14250 battery process, wherein acetylene black particles were used as the positive electrode, metallic lithium was used as the negative electrode, and the solution prepared in each embodiment and comparative example was used as the electrolyte. The configured ER14250 lithium thionyl chloride battery was subjected to 330Ω and 1000Ω constant resistance discharge at room temperature to obtain the performance test data shown in Table 1.

[0059] Table 1 Test data results

[0060] Carbon tetrachloride content 330Ω discharge time 1000Ω discharge time Example 1 5％ 119.6 h 320.9h Example 2 8％ 128.1h 340.3h Example 3 10％ 124.7h 337.2h Comparative Example 1 0％ 113.9h 300.9h Comparative Example 2 2％ 114.1h 302.6h Comparative Example 3 12％ 106.6h 280.8h

[0061] Combining Table 1 and Figures 1-2 It can be seen that the battery configured in Example 1 has a 330Ω constant group discharge time of 119.6h at room temperature, which is 4.9% longer than that in Comparative Example 1; the 1000Ω constant group discharge time is 320.9h, which is 6.6% longer than that in Comparative Example 1. The battery configured in Example 2 has a 330Ω constant group discharge time of 128.1h at room temperature, which is 12.3% longer than that in Comparative Example 1; the 1000Ω constant group discharge time is 340.3h, which is 13.1% longer than that in Comparative Example 1. The battery configured in Example 3 has a 330Ω constant group discharge time of 124.7h at room temperature, which is 9.5% longer than that in Comparative Example 1; the 1000Ω constant group discharge time is 337.2h, which is 12.1% longer than that in Comparative Example 1.

[0062] From the above results, it can be seen that in Comparative Example 1, no carbon tetrachloride is added, and the discharge time is the shortest. This should be due to the fact that the sulfur generated during the discharge process adheres to the surface of the carbon positive electrode, causing the battery to deactivate; in Comparative Example 2, the amount of carbon tetrachloride added is 2%, and the discharge time is equivalent to the discharge time of Comparative Example 1, indicating that the amount of carbon tetrachloride added is too little, and the effect of dissolving sulfur cannot be achieved, so the discharge time is not improved compared with Comparative Example 1; when the amount of carbon tetrachloride added is too much, such as when the amount added is 12%, the discharge time is shorter than the discharge time when it is not added. This is because although carbon tetrachloride can partially dissolve the sulfur generated during the discharge process and effectively alleviate the passivation of the positive electrode, excessive addition will cause the content of active substance thionyl chloride in the electrolyte to decrease, resulting in a reduction in battery capacity. It can be seen that the optimal amount of carbon tetrachloride added is between 5% and 10%, which will not only not excessively reduce the mass proportion of active substance thionyl chloride in the electrolyte and reduce the battery capacity, but also partially dissolve the sulfur generated during the discharge process, exposing more reactive sites, thereby alleviating the passivation of the positive electrode, and thus obtaining a relatively long discharge time.

[0063] Comparative Example 4

[0064] The only difference between this comparative example and Example 1 is that benzene, which can also dissolve sulfur, is used as an additive, but benzene reacts with thionyl chloride in the electrolyte, so this solution cannot be carried out.

[0065] Comparative Example 5

[0066] The only difference between this comparative example and Example 1 is that toluene, which can also dissolve sulfur, is used as an additive, but toluene reacts with thionyl chloride in the electrolyte, so this solution cannot be carried out.

[0067] Comparative Example 6

[0068] The only difference between this comparative example and Example 1 is that dimethyl sulfoxide, which can also dissolve sulfur, is used as an additive, but dimethyl sulfoxide reacts with thionyl chloride in the electrolyte, so this solution cannot be carried out.

[0069] Comparative Example 7

[0070] The only difference between this comparative example and Example 1 is that disulfur dichloride, which can also dissolve sulfur, is used as an additive, but disulfur dichloride will react with the negative electrode metal lithium, so this solution cannot be carried out.

[0071] Comparative Example 8

[0072] The difference between this comparative example and Example 1 is that carbon disulfide, which can also dissolve sulfur, is used as an additive. However, carbon disulfide is extremely flammable and explosive, especially when it comes into contact with sparks, flames or oxidants (thionyl chloride is a strong oxidant), so this solution cannot be carried out.

[0073] In summary, due to the particularity of lithium thionyl chloride batteries (the negative electrode is lithium, which has strong reducing properties; the electrolyte solvent is thionyl chloride, which has strong oxidizing properties), its lithium negative electrode or electrolyte is easy to react with most solvents that can dissolve sulfur. Therefore, only carbon tetrachloride is the most suitable additive. When the amount of carbon tetrachloride added is controlled between 5% and 10%, the battery discharge time can be extended.

[0074] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing an electrolyte for a high-capacity lithium thionyl chloride battery, characterized in that: The method comprises the following steps: Step 1, preparing constituent raw materials; purifying thionyl chloride and carbon tetrachloride respectively, and drying lithium tetrachloroaluminate and sulfur dioxide; Step 2: under dry conditions, adding the lithium tetrachloroaluminate pretreated in step 1 to thionyl chloride, stirring, and preparing a premix; Step 3: Place the lithium sheet into the premix of step 2, heat and reflux at 60-70°C until the lithium sheet turns black, filter, take another lithium sheet and place it into the filtered premix, and continue to reflux for 1 hour. If the lithium sheet does not turn black, the impurity removal is completed; if the lithium sheet turns black, continue to repeat the above operation until the lithium sheet is not obviously black; Step 4: adding the carbon tetrachloride pretreated in step 1 to the premix after impurities are removed in step 3, and introducing sulfur dioxide gas to obtain an electrolyte.

2. The method for preparing an electrolyte for a high-capacity lithium thionyl chloride battery according to claim 1, characterized in that: In step 1, the thionyl chloride and carbon tetrachloride are purified separately, comprising: Thionyl chloride and carbon tetrachloride were purified separately by distillation in a fume hood.

3. The method for preparing the electrolyte of the high-capacity lithium thionyl chloride battery according to claim 2, characterized in that: In step 1, the drying of lithium tetrachloroaluminate comprises: Lithium tetrachloroaluminate was vacuum dried at 60°C for 12 h, and then replaced with dry argon three times and vacuum dried at 60°C for another 12 h.

4. The method for preparing an electrolyte for a high-capacity lithium thionyl chloride battery according to claim 3, characterized in that: In step 1, the drying of sulfur dioxide comprises: Pass sulfur dioxide into a scrubbing bottle filled with molecular sieves.

5. The method according to claim 4, characterized in that The molecular sieve is a 3A type molecular sieve.

6. The method for preparing an electrolyte for a high-capacity lithium thionyl chloride battery according to claim 1, characterized in that: In step 2, the concentration of lithium tetrachloroaluminate in the premix is ​​1 mol / L.

7. An electrolyte for a high-capacity lithium thionyl chloride battery, characterized in that: The electrolyte is prepared by the preparation method according to any one of claims 1 to 6.

8. The electrolyte of the high-capacity lithium thionyl chloride battery according to claim 7, comprising thionyl chloride and lithium tetrachloroaluminate, characterized in that: The invention also comprises carbon tetrachloride, wherein the carbon tetrachloride accounts for 5-10% of the total mass of the thionyl chloride and the lithium tetrachloroaluminate.

9. The electrolyte of the high-capacity lithium thionyl chloride battery according to claim 8, characterized in that: The invention also comprises sulfur dioxide, wherein the sulfur dioxide accounts for 5% of the total mass of the thionyl chloride and the lithium tetrachloroaluminate.

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