A method for improving storage reliability of lithium thionyl chloride batteries

Abstract

The present invention proposes a method for improving the storage reliability of lithium thionyl chloride batteries. The battery comprises a carbon positive electrode, a metal lithium negative electrode and a SOCl2 electrolyte / active substance. The method generates a passivation film on the surface of the metal lithium negative electrode to improve the storage reliability of the lithium thionyl chloride battery. The present invention generates a dense passivation film (SEI film) in situ on the surface of the metal lithium negative electrode through an electrochemical pre-filming method. The main component of the passivation film is LiF, which is thin and dense and allows ions to pass through. Compared with the passivation film mainly composed of LiCl generated by SOCl2 and metal lithium, its properties are more stable and will not continue to grow and thicken. Therefore, it can effectively improve the storage reliability of lithium thionyl chloride batteries and alleviate the voltage hysteresis and failure caused by the excessive thickness of the passivation film.

Description

Technical Field

[0001] The invention relates to the technical field of lithium primary batteries, and in particular to a method for improving the storage reliability of lithium thionyl chloride batteries. Background Art

[0002] Li / SOCl2 battery (full name "lithium thionyl chloride battery", also known as "lithium thionyl chloride battery") has the advantages of high operating voltage, long storage life, wide operating temperature range, easy use and maintenance, and strong adaptability. In the past decade, it has been widely used in the national economy represented by the defense field.

[0003] Li / SOCl2 battery adopts (-)Li┃LiAlCl4 / SOCl2┃C(+) electrochemical system. The negative electrode active material is metallic Li, the positive electrode active material is thionyl chloride (SOCl2), carbon (C) is the reduction carrier of SOCl2, and the electrolyte is lithium tetrachloroaluminate (LiAlCl4) SOCl2 solution.

[0004] Lithium-ion batteries are prone to voltage hysteresis, battery swelling, leakage and failure after long-term storage at high temperatures. The reason for the decline in battery reliability is generally believed to be the reaction between the electrolyte and the lithium negative electrode to form a passivation film mainly composed of LiCl. The passivation film becomes thicker over time and grows into a loose and porous multi-level structure, which increases the resistance to ion transmission, thereby causing voltage hysteresis and even failure.

[0005] In response to the above problems, domestic and foreign research has mainly focused on functional additives to electrolytes and replacement of lithium salts. Research results show that these methods have limited effects.

[0006] Therefore, it is urgent to develop a new method to improve the storage reliability of lithium-ion batteries. Summary of the invention

[0007] In view of this, the present invention proposes a method for improving the storage reliability of lithium thionyl chloride batteries. A dense passivation film is generated on the surface of the negative electrode by an electrochemical pre-filming method. The passivation film has excellent stability and will not continue to react and become thicker over time, thereby effectively improving the storage reliability of the lithium thionyl chloride battery.

[0008] The invention provides a method for improving the storage reliability of a lithium thionyl chloride battery. The battery comprises a carbon positive electrode, a metal lithium negative electrode and a SOCl2 electrolyte. The method generates a passivation film on the surface of the metal lithium negative electrode to improve the storage reliability of the lithium thionyl chloride battery.

[0009] On the basis of the above technical solution, preferably, the metal lithium negative electrode is passivated by an electrochemical method to generate the passivation film.

[0010] On the basis of the above technical solution, preferably, the passivation treatment comprises the following steps:

[0011] Step 1: Injection and soaking

[0012] Immersing the metallic lithium negative electrode in an electrolytic cell containing a lithium salt electrolyte;

[0013] Step 2: Power on

[0014] Connect the negative terminal of the DC formation equipment to the metal lithium negative electrode, and connect to the positive terminal at the same time, start the equipment, and complete the formation;

[0015] Step 3: Cleaning

[0016] Disconnect the equipment, take out the metal lithium negative electrode, and use an organic solvent to clean the formed metal lithium negative electrode;

[0017] Step 4: Drying

[0018] The metal lithium negative electrode cleaned in step 3 is dried to obtain a metal lithium negative electrode after passivation treatment.

[0019] On the basis of the above technical scheme, in order to facilitate subsequent operations, step one and step two can be carried out in a cylindrical steel shell. The specific operations are as follows: the metal lithium negative electrode and the glass fiber diaphragm are distributed and loaded into the cylindrical steel shell in the conventional way of assembling lithium thionyl chloride batteries, the negative terminal of the DC formation equipment is connected to the stainless steel shell, and the positive terminal is connected to the inert electrode, which is a platinum electrode; when performing the cleaning work in step three, an organic solvent is required to be used to clean the metal lithium negative electrode and the glass fiber diaphragm after formation.

[0020] On the basis of the above technical solution, preferably, in step 1, in the electrolyte, the solvent is selected from carbonates, and the lithium salt is selected from LiFSA (lithium bis(fluorosulfonylamide)) and / or LiTFSA (lithium bis(trifluoromethylsulfonylamide)).

[0021] More preferably, the solvent is PC (propylene carbonate).

[0022] Based on the above technical solution, preferably, the concentration of the lithium salt is 4 to 5 mol / L.

[0023] On the basis of the above technical solution, preferably, the lithium salt electrolyte contains a film-forming additive; the film-forming additive is selected from LiPO2F2 with a concentration of 0.05 to 0.1 mol / L.

[0024] On the basis of the above technical solution, preferably, in step 2, the formation conditions include: the current is selected from 0.01 to 0.15 C, and the time is selected from 10 to 15 min.

[0025] On the basis of the above technical solution, preferably, in step three, the cleaning requirement is: cleaning until the lithium salt concentration in the washing liquid is lower than 0.03 mol / L.

[0026] On the basis of the above technical solution, preferably, the organic solvent is selected from dimethyl ether (DME) or dimethyl carbonate (DMC).

[0027] Based on the above technical solution, preferably, in step 4, the drying temperature is 35-40°C.

[0028] The method provided by the present invention has the following beneficial effects compared with the prior art:

[0029] The present invention generates a dense passivation film (SEI film) in situ on the surface of the metal lithium negative electrode by an electrochemical pre-filming method. The main component of the passivation film is LiF, which is thin and dense and allows ions to pass through. Compared with the passivation film mainly composed of LiCl generated by SOCl2 and metal lithium, its properties are more stable and will not continue to grow and thicken. Therefore, it can effectively improve the storage reliability of lithium thionyl chloride batteries and alleviate the voltage hysteresis and failure caused by the excessive thickness of the passivation film. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] 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.

[0031] Figure 1 Schematic diagram of electrochemical pre-film formation;

[0032] Figure 2 This is a comparison diagram of initial discharge curves of Examples 1 to 3 of the present invention;

[0033] Figure 3 This is a comparison diagram of initial discharge curves of Example 1 of the present invention and Comparative Example 1;

[0034] Figure 4 This is a comparison diagram of initial discharge curves of Example 1 of the present invention and Comparative Example 2;

[0035] Figure 5 This is a comparison diagram of initial discharge curves of Example 1 of the present invention and Comparative Example 3;

[0036] Figure 6 It is a comparison diagram of the initial discharge curves of Example 1 of the present invention and a commercially available lithium thionyl chloride battery. DETAILED DESCRIPTION

[0037] 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.

[0038] Example 1

[0039] This embodiment provides a passivation treatment method for a metal lithium negative electrode, comprising the following steps:

[0040] Preparation of electrolyte: Add 0.4 mol of lithium salt LiFSA into 100 ml of PC-based electrolyte. After the lithium salt is dissolved, weigh 0.1 mol of film-forming additive LiPO2F2 and add it to the electrolyte.

[0041] Passivation treatment: refer to the attached Figure 1 , inject the prepared electrolyte into the cylindrical steel shell containing the metal lithium negative electrode and the glass fiber diaphragm, so that the electrolyte covers the metal lithium negative electrode; connect the negative terminal of the DC formation equipment to the cylindrical shell of the battery, and connect the positive terminal of the DC formation equipment to a platinum electrode, and immerse the platinum electrode in the electrolyte. Use a 0.01C rate to form the negative electrode for 10 minutes; take out the platinum electrode, disconnect the formation equipment, and use DMC solvent to clean the metal lithium negative electrode and glass fiber diaphragm after formation until the lithium salt concentration in the washing liquid is lower than 0.03 mol / L, then dry the cleaned metal lithium negative electrode, glass fiber diaphragm, and steel shell at 30°C under vacuum conditions to obtain a metal lithium negative electrode with a passivation film on the surface.

[0042] Example 2

[0043] This embodiment provides a passivation treatment method for a metal lithium negative electrode, comprising the following steps:

[0044] Preparation of electrolyte: Add 0.4 mol of lithium salt LiFSA into 100 ml of PC-based electrolyte. After the lithium salt is dissolved, weigh 0.1 mol of film-forming additive LiPO2F2 and add it to the electrolyte.

[0045] Passivation treatment: Inject the prepared electrolyte into the cylindrical steel shell containing the metal lithium negative electrode and the glass fiber diaphragm, so that the electrolyte covers the metal lithium negative electrode; connect the negative terminal of the DC formation equipment to the cylindrical shell of the battery, and connect the positive terminal of the DC formation equipment to a platinum electrode, and immerse the platinum electrode in the electrolyte. Use a 0.05C rate to form the negative electrode for 10 minutes; take out the platinum electrode, disconnect the formation equipment, and use DMC solvent to clean the metal lithium negative electrode and glass fiber diaphragm after formation until the lithium salt concentration in the washing liquid is lower than 0.03mol / L, then dry the cleaned metal lithium negative electrode, glass fiber diaphragm, and steel shell at 30°C under vacuum conditions to obtain a metal lithium negative electrode with a passivation film on the surface.

[0046] Example 3

[0047] This embodiment provides a passivation treatment method for a metal lithium negative electrode, comprising the following steps:

[0048] Preparation of electrolyte: Add 0.4 mol of lithium salt LiFSA into 100 ml of PC-based electrolyte. After the lithium salt is dissolved, weigh 0.1 mol of film-forming additive LiPO2F2 and add it to the electrolyte.

[0049] Passivation treatment: Inject the prepared electrolyte into the cylindrical steel shell containing the metal lithium negative electrode and the glass fiber diaphragm, so that the electrolyte covers the metal lithium negative electrode; connect the negative terminal of the DC formation equipment to the cylindrical shell of the battery, and connect the positive terminal of the DC formation equipment to a platinum electrode, and immerse the platinum electrode in the electrolyte. Use a 0.15C rate to form the negative electrode for 10 minutes; take out the platinum electrode, disconnect the formation equipment, and use DMC solvent to clean the metal lithium negative electrode and glass fiber diaphragm after formation until the lithium salt concentration in the washing liquid is lower than 0.03 mol / L, then dry the cleaned metal lithium negative electrode, glass fiber diaphragm, and steel shell at 30°C under vacuum conditions to obtain a metal lithium negative electrode with a passivation film on the surface.

[0050] Example 4

[0051] This embodiment provides a passivation treatment method for a metal lithium negative electrode, comprising the following steps:

[0052] Preparation of electrolyte: Add 0.4 mol of lithium salt LiFSA into 100 ml of PC-based electrolyte. After the lithium salt is dissolved, add 0.05 mol of film-forming additive LiPO2F2 into the electrolyte.

[0053] Passivation treatment: Inject the prepared electrolyte into the cylindrical steel shell containing the metal lithium negative electrode and the glass fiber diaphragm, so that the electrolyte covers the metal lithium negative electrode; connect the negative terminal of the DC formation equipment to the cylindrical shell of the battery, and connect the positive terminal of the DC formation equipment to a platinum electrode, and immerse the platinum electrode in the electrolyte. Use a 0.05C rate to form the negative electrode for 10 minutes; take out the platinum electrode, disconnect the formation equipment, and use DMC solvent to clean the metal lithium negative electrode and glass fiber diaphragm after formation until the lithium salt concentration in the washing liquid is lower than 0.03mol / L, then dry the cleaned metal lithium negative electrode, glass fiber diaphragm, and steel shell at 35°C under vacuum conditions to obtain a metal lithium negative electrode with a passivation film on the surface.

[0054] Example 5

[0055] This embodiment provides a passivation treatment method for a metal lithium negative electrode, comprising the following steps:

[0056] Preparation of electrolyte: Add 0.4 mol of lithium salt LiTFSA into 100 ml of PC-based electrolyte. After the lithium salt is dissolved, add 0.08 mol of film-forming additive LiPO2F2 into the electrolyte.

[0057] Passivation treatment: Inject the prepared electrolyte into the cylindrical steel shell containing the metal lithium negative electrode and the glass fiber diaphragm, so that the electrolyte covers the metal lithium negative electrode; connect the negative terminal of the DC formation equipment to the cylindrical shell of the battery, and connect the positive terminal of the DC formation equipment to a platinum electrode, and immerse the platinum electrode in the electrolyte. Use a 0.1C rate to form the negative electrode for 12 minutes; take out the platinum electrode, disconnect the formation equipment, and use DMC solvent to clean the metal lithium negative electrode and glass fiber diaphragm after formation until the lithium salt concentration in the washing liquid is lower than 0.03 mol / L, then dry the cleaned metal lithium negative electrode, glass fiber diaphragm, and steel shell at 35°C under vacuum conditions to obtain a metal lithium negative electrode with a passivation film on the surface.

[0058] Example 6

[0059] This embodiment provides a passivation treatment method for a metal lithium negative electrode, comprising the following steps:

[0060] Preparation of electrolyte: Add 0.5 mol of lithium salt LiTFSA into 100 ml of PC-based electrolyte. After the lithium salt is dissolved, add 0.1 mol of film-forming additive LiPO2F2 into the electrolyte.

[0061] Passivation treatment: Inject the prepared electrolyte into the cylindrical steel shell containing the metal lithium negative electrode and the glass fiber diaphragm, so that the electrolyte covers the metal lithium negative electrode; connect the negative terminal of the DC formation equipment to the cylindrical shell of the battery, and connect the positive terminal of the DC formation equipment to a platinum electrode, and immerse the platinum electrode in the electrolyte. Use a 0.15C rate to form the negative electrode for 15 minutes; take out the platinum electrode, disconnect the formation equipment, and use DMC solvent to clean the metal lithium negative electrode and glass fiber diaphragm after formation until the lithium salt concentration in the washing liquid is lower than 0.03 mol / L, then dry the cleaned metal lithium negative electrode, glass fiber diaphragm, and steel shell at 40°C under vacuum conditions to obtain a metal lithium negative electrode with a passivation film on the surface.

[0062] Comparative Example 1

[0063] The difference from Example 1 is that when the passivation treatment is performed, step 3 is not performed, and the other steps remain unchanged.

[0064] Comparative Example 2

[0065] The difference from Example 1 is that the lithium salt LiFSI is used to replace the lithium salt LiFSA, and the other steps remain unchanged.

[0066] Comparative Example 3

[0067] The difference from Example 1 is that the film-forming additive is replaced with 0.1 mol VC, and the other steps remain unchanged.

[0068] The embodiments 1 to 6 and comparative examples 1 to 3 were assembled into lithium thionyl chloride batteries according to conventional methods. Taking the embodiments 1 to 3 as examples, the following performance tests were performed on the above embodiments 1 to 3 and comparative examples 1 to 3, including:

[0069] After the battery was stored in a 55°C high temperature oven for 30 days, it was taken out and discharged at a rate of 0.05C.

[0070] Test results such as Figures 2 to 4 shown.

[0071] Through Examples 1 to 3, combined Figure 2 It can be seen that when the formation current is 0.01C, the voltage hysteresis during activation is the smallest, so the thickness and density of the metal lithium negative electrode film are optimal.

[0072] Through Example 1 and Comparative Example 1, combined Figure 3 It can be seen that the voltage drops greatly during activation, so the effect of the SEI film formed on the lithium negative electrode without a separator is worse than that after the lithium negative electrode and the separator are cleaned together.

[0073] Through Example 1 and Comparative Example 2, combined Figure 4It can be seen that after the lithium salt added during film formation is replaced by LiFSI from LiFSA, the lithium-ion battery after storage has a significant voltage drop at the beginning of discharge. After comparison, the effect is not as good as that of lithium salt LiFSA. It is speculated that this may be because in this system, LiFSA has a better film-forming effect and is more compatible with thionyl chloride. Therefore, the lithium salt LiFSA has a better effect.

[0074] Through Example 1 and Comparative Example 3, combined Figure 5 It can be seen that when the film-forming additive LiPO2F2 is replaced with VC, a commonly used film-forming additive for lithium-ion batteries, the lithium-ion battery after storage has a significant voltage drop at the beginning of discharge. After comparison, the effect is not as good as the additive LiPO2F2. It is speculated that the integrity, thickness, composition, etc. of the film are not compatible with the thionyl chloride system. Therefore, the additive LiPO2F2 has a better effect.

[0075] The metal lithium negative electrode after passivation treatment in Example 1 is used to assemble a lithium thionyl chloride battery, comprising the following steps:

[0076] Preparation of pelletized positive electrode: acetylene black (1kg), alcohol (1kg), deionized water (3kg), polytetrafluoroethylene emulsion (100g) were mixed and stirred, and the powder was crushed in a rotary granulator; the crushed material was poured into a shot blasting machine, the temperature was set at 80℃, and the speed was 300r / min for 10min, and the material was discharged. The pelletized particles on the plate were then dried in an oven at 150℃ for 12h; the temperature was then set to 250℃, and the fiberization treatment was performed for 5min; finally, the particles were broken up in a mixer, and then the particles were sieved and stored for later use.

[0077] Assembly of lithium-ion battery: Pour the pelletized positive electrode particles into the battery shell, install the cover assembly and weld it. After welding, inject SOCl2 electrolyte containing LiAlCl4 from the injection hole, and seal it to obtain a lithium-ion battery cell.

[0078] The ER26500 lithium thionyl chloride battery was purchased from the Korean manufacturer Star Sun Moon. It was placed at 55°C for 30 days and then taken out for discharge. The discharge curves were compared with those of the lithium thionyl chloride battery assembled above. Figure 5 shown.

[0079] Depend on Figure 6 It can be seen that in conventional lithium-ion batteries, a passivation film mainly composed of LiCl is generated due to the reaction between thionyl chloride and the metallic lithium negative electrode. The passivation film becomes thicker over time, resulting in voltage hysteresis when the battery is activated. The present invention generates a denser SEI film mainly composed of LiF on the lithium negative electrode in advance, which can prevent thionyl chloride from continuously reacting with metallic lithium, thereby eliminating voltage hysteresis.

[0080] 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 improving the storage reliability of a lithium thionyl chloride battery, the battery comprising a carbon positive electrode, a metal lithium negative electrode and a SOCl2 electrolyte / active material, characterized in that: The method enables a passivation film to be formed on the surface of a metallic lithium negative electrode, so as to improve the storage reliability of a lithium thionyl chloride battery.

2. The method according to claim 1, characterized in that The metal lithium negative electrode is passivated by an electrochemical method to generate the passivation film.

3. The method according to claim 2, characterized in that The passivation treatment comprises the following steps: Step 1: Injection and soaking Immersing the metallic lithium negative electrode in an electrolytic cell containing an electrolyte; Step 2: Power on Connect the negative terminal of the DC formation equipment to the negative electrode of the metal lithium, and connect the positive terminal to the inert electrode immersed in the electrolyte, start the equipment, and complete the formation; Step 3: Cleaning Disconnect the equipment, take out the metal lithium negative electrode, and use an organic solvent to clean the formed metal lithium negative electrode; Step 4: Drying The metal lithium negative electrode cleaned in step 3 is dried to obtain a metal lithium negative electrode after passivation treatment.

4. The method according to claim 3, characterized in that In step 1, in the electrolyte, the solvent is selected from carbonates; and the lithium salt is selected from LiFSA and / or LiTFSA.

5. The method according to claim 4, characterized in that The concentration of the lithium salt is 4-5 mol / L.

6. The method according to claim 5, characterized in that The lithium salt electrolyte contains a film-forming additive; the film-forming additive is selected from LiPO2F2 with a concentration of 0.05 to 0.1 mol / L.

7. The method according to claim 3, characterized in that In step 2, the formation conditions include: the current is selected from 0.01 to 0.15C, and the time is selected from 10 to 15 minutes.

8. The method according to claim 3, characterized in that In step three, the cleaning requirement is: cleaning until the lithium salt concentration in the washing solution is lower than 0.03 mol / L.

9. The method according to claim 3, characterized in that In step 4, the drying temperature is 35-40°C.

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