A surface modification method for lithium alloy anodes in primary lithium batteries

Abstract

This invention belongs to the field of primary lithium battery technology, specifically relating to a surface modification method for the lithium alloy anode of a primary lithium battery. It employs trifluoromethane-silver trioxide modification of the Li-B alloy to form a surface layer containing metallic silver, LiF, and sulfides. This method constructs a surface layer with high stability and high lithium-ion conductivity on the lithium alloy surface, effectively protecting the metallic lithium, reducing surface impedance, and eliminating electrochemical noise, thereby extending the storage life of the primary lithium battery and improving its electrochemical performance. The method is simple, practical, and efficient, with strong application prospects.

Description

Technical Field

[0001] This invention belongs to the field of primary lithium battery technology, specifically relating to a surface modification method for a lithium alloy negative electrode of a primary lithium battery. Background Technology

[0002] Primary lithium batteries refer to batteries that use lithium metal or lithium alloy as the negative electrode and do not require recharging after a single discharge. These include primary lithium batteries (lithium sulfur dioxide batteries, lithium carbon fluoride batteries, lithium thionyl chloride batteries, etc.) and reserve lithium batteries (reserve lithium thionyl chloride batteries, reserve lithium sulfur batteries, etc.). To address lithium battery safety, replacing metallic lithium with lithium alloys can improve safety. However, the following issues remain to be addressed: 1. Primary lithium batteries require long-term storage before discharge, necessitating protection of the negative electrode to prevent corrosion of the metallic lithium and subsequent capacity reduction; 2. Batteries need to output stable electrical signals promptly during operation, avoiding electrochemical noise; 3. Lithium alloys have higher impedance than metallic lithium, leading to increased internal resistance and decreased electrochemical performance.

[0003] Currently, lithium alloys are mainly protected through two methods: one is to composite lithium metal with a substrate material through mechanical pressure, high-temperature melting and wetting, and electrochemical deposition to construct a composite metal anode. However, the preparation of composite electrodes requires attention to the following: 1) The study of the substrate material must fully consider whether lithium can be uniformly deposited within its pore structure. Unmodified substrate materials generally do not have lithium affinity, so further treatment of the substrate material is required, such as surface activation, etching, doping, and plating, to improve the lithium affinity of the substrate material; 2) For metal matrix frameworks (foamed copper, foamed nickel, etc.), it is difficult to obtain composite lithium anodes with high specific capacity because the density of the metal matrix is ​​much higher than that of lithium. Compared with lithium dendrites, three-dimensional metal substrate materials are more likely to puncture the separator and cause short circuits; 3) The high-temperature melting method poses significant safety hazards.

[0004] Secondly, physical / chemical protective layers are added to the lithium alloy surface. Physical protective layers can be constructed on the lithium alloy surface using processes such as atomic layer deposition, hard template methods, sputtering, and spin coating. This method requires high precision in controlling the ionic / electronic conductivity, mechanical strength, and flexibility of the physical protective film, and it is difficult to regulate local lithium deposition behavior using only physical protection methods. Although the high reactivity between metallic lithium and the electrolyte can allow for the in-situ formation of a surface layer similar to an SEI film on the lithium metal surface, and adjusting the lithium salt and using electrolyte additives are common strategies for in-situ SEI formation, the formation of the in-situ SEI film consumes some lithium ions, increasing the irreversible capacity during the first charge-discharge cycle and reducing the charge-discharge efficiency of the electrode material.

[0005] Patent application number 202210715428.9 discloses a method for preparing a lithium metal anode protective layer hybridized with lithium fluoride and organofluorine compounds, a lithium metal anode, and a lithium battery. This method involves completely dispersing a liquid heptadecafluorodecyltrimethoxysilane in N-methylpyrrolidone to form a milky white solution, then coating this solution onto a lithium metal foil. After standing at room temperature until the solution evaporates, a lithium metal anode protective layer hybridized with lithium fluoride and organofluorine compounds is formed. This technical solution constructs a bilayer protective layer through the chemical reaction of heptadecafluorodecyltrimethylsiloxane on lithium metal. This protective layer effectively inhibits the formation of lithium dendrites and dead lithium, reduces electrolyte consumption, and significantly improves the cycle stability of the lithium metal battery. The lithium metal anode obtained by constructing this protective layer can be matched with commonly used commercially available ether-based and ester-based electrolytes, thereby obtaining a high-performance lithium metal battery.

[0006] Patent application number 201810104762.4 discloses a surface modification method for lithium anodes in lithium metal batteries and a lithium metal battery. The modification method includes the following steps: immersing a lithium metal anode in a fluorine-containing ionic liquid under a dry protective gas atmosphere, or applying a fluorine-containing ionic liquid to the surface of the lithium metal anode; after fluorination, removing the anode; and forming a protective layer rich in lithium fluoride on the surface of the lithium metal anode, thus obtaining a lithium fluoride-coated lithium metal anode. This technical solution yields a highly uniform and dense lithium fluoride protective layer through surface fluorination, which reduces the consumption of lithium metal and electrolyte, inhibits the formation of lithium dendrites, and gives the lithium metal anode advantages such as higher discharge specific capacity, longer cycle life, and better safety performance. This achieves stability and high efficiency of lithium metal batteries during long-cycle operation, meeting the requirements for high-energy, high-power power batteries.

[0007] Patent application number 201710044381.7 discloses an interface modification method for the negative electrode of a lithium metal battery. This surface-modified lithium metal can be applied to lithium metal batteries. The invention uses a solution containing heterogeneous metal ions such as copper, manganese, cobalt, nickel, iron, zinc, gold, silver, and platinum as the treatment liquid, and generates a heterogeneous metal film in situ on the lithium sheet surface through a liquid-phase chemical displacement method. This heterogeneous metal film can stabilize the lithium metal / electrolyte interface, effectively suppress the formation of lithium dendrites, reduce electrochemical polarization, improve the rechargeability of the lithium metal negative electrode, and thus improve the performance of the lithium metal battery.

[0008] The three representative patents mentioned above are mainly aimed at lithium metal secondary batteries that can be repeatedly charged and discharged. The goal is to suppress lithium dendrites generated during repeated charging and discharging, so that the battery has higher safety and better electrical performance. However, for the problems faced by the lithium alloy negative electrode in primary lithium batteries with only one discharge process, there is currently no effective solution reported.

[0009] Through in-depth research, the inventors learned that LiF's good hardness and stability give the SEI film high strength, effectively protecting lithium metal. However, LiF's high ion tunneling migration barrier also reduces the diffusion kinetics of Li+ through the SEI, resulting in low Li+ conductivity of the SEI. Low Li+ conductivity increases electrode polarization potential, which is detrimental to the exchange and conduction of lithium ions between the electrode and the electrolyte. Therefore, it is necessary to design a surface layer with multiple compositions to simultaneously meet the common requirements of primary lithium-ion battery lithium alloy anodes for protecting lithium metal, reducing alloy interface impedance, and eliminating electrochemical noise. Summary of the Invention

[0010] This invention addresses the shortcomings of existing technologies by proposing a surface modification method for lithium alloy anodes in primary lithium batteries.

[0011] Specifically, this is achieved through the following technical solutions:

[0012] A surface modification method for a primary lithium-ion battery lithium alloy negative electrode involves modifying a Li-B alloy with silver trifluoromethane mercaptan to generate a surface layer containing metallic silver, LiF, and sulfides on the Li-B alloy surface.

[0013] The sulfide is Li-S.

[0014] A surface modification method for a lithium alloy anode of a primary lithium battery includes the following steps:

[0015] Step 1: Dissolve silver trifluoromethane mercaptan in an organic solvent to prepare a reaction solution;

[0016] The mass concentration of silver trifluoromethane mercaptan in the reaction solution is 0.5-10%; preferably 0.5%.

[0017] The organic solvent is any one or more of diethyl ether, tetrahydrofuran, ethylene glycol dimethyl ether, and dichloromethane; preferably a tetrahydrofuran solution.

[0018] The tetrahydrofuran solution is first dehydrated using a lithium molecular sieve for 24–72 hours to avoid the influence of water molecules.

[0019] Step 2: Select a bright Li-B alloy strip and cut it into Li-B alloy discs with a diameter of 16mm using a manual punching machine;

[0020] Step 3: Place the Li-B alloy disc in the reaction solution from Step 1 and stir to perform thorough surface modification;

[0021] The stirring process conditions are a rotation speed of 300-600 rpm and a time of 10-60 min; preferably, the stirring process conditions are a rotation speed of 300 rpm and a time of 30 min.

[0022] Step 4: Clean and dry the alloy disc obtained in Step 3 to obtain a Li-B alloy with a surface rich in metallic silver, Li-F, and Li-S.

[0023] The present invention relates to the application of a primary lithium alloy negative electrode in the assembly of a primary lithium battery, wherein the electrolyte of the primary lithium battery contains one or two film-forming additives selected from vinylene carbonate (VC) and fluoroethylene carbonate (FEC).

[0024] Beneficial effects:

[0025] The method of the present invention constructs a surface layer with high stability and high lithium-ion conductivity on the surface of a lithium-boron alloy.

[0026] This invention utilizes the reaction of silver trifluoromethanethiol (AgSCF3) with Li-B alloys in THF or other organic solutions to construct a surface layer rich in metallic silver (Ag), LiF, and sulfides on the surface of lithium alloys. The prepared surface layer effectively protects the lithium in the alloy, reduces the interfacial impedance of the alloy, and eliminates electrochemical noise.

[0027] The method of this invention is a multi-modification method, which is mild, practical and efficient.

[0028] Using MnO2 as the positive electrode material to assemble primary lithium batteries, the batteries with surface-modified negative electrodes exhibit superior electrical performance compared to batteries using the original Li-B alloy. Attached Figure Description

[0029] Figure 1 This is a diagram showing the modification process of the Li-B alloy;

[0030] Figure 2 The images show scanning electron microscope (SEM) images of the surface and cross-section of the Li-B alloy disc obtained in Example 1 and the original Li-B alloy disc; where a represents the surface of the original Li-B, b represents the surface of the Li-B obtained in Example 1, c represents the cross-section of the original Li-B, and d represents the cross-section of the Li-B obtained in Example 1.

[0031] Figure 3 The distribution of different elements on the surface of the lithium-boron alloy disc obtained in Example 1;

[0032] Figure 4 EDX results for different elements on the surface of the lithium-boron alloy disc obtained in Example 1;

[0033] Figure 5 The discharge results of Li-B alloys assembled into batteries before and after AgSCF3 surface modification and before and after being placed in storage;

[0034] Figure 6Symmetric cells assembled from Li-B alloys before and after AgSCF3 modification at 1 mA·cm -2 Current density and 1 mAh·cm -2 Comparison of cycle stability at different lithium deposition capacities;

[0035] Figure 7 Electrochemical impedance spectroscopy (EIC) spectra of the Li-B / MnO2 battery in Example 1 and the Li-B / MnO2 battery in the control example;

[0036] Figure 8 This is a schematic diagram showing the performance of the Li-B / MnO2 battery of Example 1 and the Li-B / MnO2 battery of the control example at different discharge rates. Detailed Implementation

[0037] The specific embodiments of the present invention will be described in further detail below, but the present invention is not limited to these embodiments. Any improvements or substitutions based on the basic spirit of these embodiments shall still fall within the scope of protection claimed by the claims of the present invention.

[0038] Example 1

[0039] A surface modification method for a lithium alloy anode of a primary lithium battery includes the following steps:

[0040] Step 1: Dissolve silver trifluoromethanethiol in tetrahydrofuran solution to prepare a reaction solution with a silver trifluoromethanethiol mass concentration of 0.5%; the tetrahydrofuran solution is first dehydrated using a lithium molecular sieve for 3 days to avoid the influence of water molecules;

[0041] Step 2: Select a bright Li-B alloy strip and cut it into Li-B alloy discs with a diameter of 16mm using a manual punching machine;

[0042] Step 3: Place the Li-B alloy disc in the reaction solution of Step 1 and stir at 300 rpm for 30 min to fully modify the surface.

[0043] Step 4: Clean and dry the alloy disc obtained in Step 3 to obtain a Li-B alloy disc with a surface rich in metallic silver, Li-F, and Li-S.

[0044] Example 1: Characterization and testing of Li-B alloys

[0045] The surface of the Li-B alloy wafer obtained in Example 1 was compared with that of the original Li-B alloy wafer. Figure 2 a is a scanning electron microscope image of the original Li-B alloy disc. Figure 2b is a scanning electron microscope (SEM) image of the Li-B alloy disc obtained in Example 1. The SEM image of the Li-B alloy disc obtained in Example 1 shows that its surface layer is a rough surface morphology composed of dense micron-sized particles. Although the cross-sections of the original and modified Li-B look similar (as shown in Figures 1-1), the surface layer of the Li-B alloy disc obtained in Example 1 is a rough surface morphology composed of dense micron-sized particles. Figure 2 c and 2d), but the elemental distribution determined by EDX clearly shows that Ag, F, and S elements are uniformly distributed on the Li-B surface ( Figure 3 The large amount of O detected on the surface likely originates from the original oxide passivation layer on the original Li-B substrate. Figure 4 The content of each element is shown in Table 1.

[0046] Element Aromic percentage (%) B 6.28 C 8.85 O 73.73 F 3.26 S 2.15 Ag 5.73

[0047] Experiment Example 2: Battery Assembly and Testing

[0048] MnO2 positive electrode sheets were punched into 14mm diameter discs and placed in the positive electrode shell. 1mol / L lithium tetrafluoroborate (LiBF4) electrolyte was added in a 1:1 volume ratio of dimethyl ether (DME): ethylene carbonate (PC). A Cellgard 2400 polypropylene membrane was placed as a separator, and electrolyte was added again. Then, a Li-B alloy sheet, a gasket, a spring, and a negative electrode shell were sequentially added. The battery was then packaged using a battery packaging machine to obtain a CR2025 coin cell. After standing for 12 hours, constant current discharge to a cutoff voltage of 1.5V was conducted in a 25℃ constant temperature testing room under different rate conditions (0.5C, 1.0C, 2.0C, 5.0C). A treatment example and a control example were set up. The Li-B alloy sheet in the treatment example was the Li-B alloy sheet obtained in Example 1 (after surface modification treatment), while the Li-B alloy sheet in the control example was the original (unmodified) Li-B alloy sheet.

[0049] Figure 5 This represents the discharge results of Li-B alloys before and after surface modification, before and after being assembled into batteries and left to stand. Figure 5 It is evident that the positive electrode specific capacities of the Li-B alloy assembled before and after surface modification, when discharged at a rate of 0.1C to 1.5V without being left to stand, are 284 mAh / g and 280 mAh / g, respectively. After the batteries are left to stand at room temperature for 100 hours, the positive electrode specific capacities when discharged at a rate of 0.1C to 1.5V are 144 mAh / g and 208 mAh / g, respectively. The results demonstrate that the surface layer effectively protects the metallic lithium in the lithium alloy, suppresses the self-discharge phenomenon of the battery, and delays the performance degradation of the primary lithium battery.

[0050] Figure 6 This presents the initial cycle test results of a symmetrical battery assembled with Li-B alloys before and after surface modification. For a primary battery, the initial discharge characteristics of the alloy directly affect the battery's performance. Figure 6 As can be seen, the unmodified alloy exhibited typical electrochemical noise during the first discharge cycle, which was eliminated only after multiple cycles. The modified alloy's negative electrode showed a smooth and stable operating voltage signal, indicating that surface modification effectively eliminated the electrochemical noise.

[0051] The impedance records for Example 1 and the control example are as follows: Figure 7 As shown, the Li-B / MnO2 battery of Example 1 has a lower impedance than the original Li-B / MnO2 battery, which is more conducive to lithium-ion transport. Figure 8 As shown in the discharge capacity diagram, regardless of the rate of discharge, the discharge capacity of Example 1 is higher than that of the control example. This demonstrates that the Li-B alloy surface modification method described in this invention can effectively improve the discharge capacity of the MnO2 primary battery. When the terminal discharge voltage is 1.5V, the specific capacities of the Li-B / MnO2 battery in Example 1 are 223, 220, 197, and 132 mAh / g, respectively, which are 27%, 32%, 82%, and 76% higher than the original Li-B / MnO2 battery under 0.5C, 1.0C, 2.0C, and 5.0C conditions, respectively. Therefore, the discharge capacity of the modified Li-B / MnO2 battery is higher than that of the original Li-B / MnO2 battery at high rates. This proves that surface modification reduces the impedance of the lithium alloy and improves the electrical performance of the battery.

[0052] In summary, this invention focuses on constructing a surface modification layer with high mechanical strength and high lithium-ion conductivity on the surface of lithium metal / alloys. Specifically, it involves reacting trifluoromethanethiol silver (AgSCF3) with a Li-B alloy to generate an artificial surface modification layer rich in LiF, lithium-containing sulfides, and metallic silver (Ag) on ​​the surface of the lithium metal / alloy electrode. Assembled Li-B / MnO2 primary lithium batteries demonstrate that the surface layer rich in LiF, sulfides, and metallic silver effectively extends battery life, reduces battery impedance, and eliminates electrochemical noise, providing a novel method for modifying lithium alloy anodes in primary lithium batteries.

[0053] Example 2

[0054] A surface modification method for a lithium alloy anode of a primary lithium battery includes the following steps:

[0055] Step 1: Dissolve silver trifluoromethanethiol in tetrahydrofuran solution to prepare a reaction solution with a silver trifluoromethanethiol mass concentration of 10%; the tetrahydrofuran solution is first dehydrated with lithium molecular sieve for 1 day to avoid the influence of water molecules;

[0056] Step 2: Select a bright Li-B alloy strip and cut it into Li-B alloy discs with a diameter of 16mm using a manual punching machine;

[0057] Step 3: Place the Li-B alloy disc in the reaction solution of Step 1 and stir at 600 rpm for 10 min to fully modify the surface.

[0058] Step 4: Clean and dry the alloy disc obtained in Step 3 to obtain a Li-B alloy disc with a surface rich in metallic silver, Li-F, and Li-S.

[0059] Example 3

[0060] A surface modification method for a lithium alloy anode of a primary lithium battery includes the following steps:

[0061] Step 1: Dissolve silver trifluoromethanethiol in tetrahydrofuran solution to prepare a reaction solution with a silver trifluoromethanethiol mass concentration of 5%; the tetrahydrofuran solution is first dehydrated with lithium molecular sieve for 1 day to avoid the influence of water molecules;

[0062] Step 2: Select a bright Li-B alloy strip and cut it into Li-B alloy discs with a diameter of 16mm using a manual punching machine;

[0063] Step 3: Place the Li-B alloy disc in the reaction solution of Step 1 and stir at 400 rpm for 60 min to fully modify the surface.

[0064] Step 4: Clean and dry the alloy disc obtained in Step 3 to obtain a Li-B alloy disc with a surface rich in metallic silver, Li-F, and Li-S.

[0065] Example 4

[0066] A surface modification method for a lithium alloy anode of a primary lithium battery includes the following steps:

[0067] Step 1: Dissolve silver trifluoromethane mercaptan in diethyl ether solution to prepare a reaction solution with a silver trifluoromethane mercaptan mass concentration of 0.5%; the diethyl ether solution is first dehydrated with lithium molecular sieve for 1 day to avoid the influence of water molecules;

[0068] Step 2: Select a bright Li-B alloy strip and cut it into Li-B alloy discs with a diameter of 16mm using a manual punching machine;

[0069] Step 3: Place the Li-B alloy disc in the reaction solution of Step 1 and stir at 300 rpm for 20 min to fully modify the surface.

[0070] Step 4: Clean and dry the alloy disc obtained in Step 3 to obtain a Li-B alloy disc with a surface rich in metallic silver, Li-F, and Li-S.

[0071] Example 5

[0072] A surface modification method for a lithium alloy anode of a primary lithium battery includes the following steps:

[0073] Step 1: Dissolve silver trifluoromethane mercaptan in dichloromethane solution to prepare a reaction solution with a silver trifluoromethane mercaptan mass concentration of 0.5%; the dichloromethane solution is first dehydrated with lithium molecular sieve for 1 day to avoid the influence of water molecules;

[0074] Step 2: Select a bright Li-B alloy strip and cut it into Li-B alloy discs with a diameter of 16mm using a manual punching machine;

[0075] Step 3: Place the Li-B alloy disc in the reaction solution of Step 1 and stir at 300 rpm for 20 min to fully modify the surface.

[0076] Step 4: Clean and dry the alloy disc obtained in Step 3 to obtain a Li-B alloy disc with a surface rich in metallic silver, Li-F, and Li-S.

[0077] Following the method in Experimental Example 2, the Li-B alloy discs from Examples 2-5 were respectively fabricated into lithium primary batteries. Then, the corresponding lithium primary batteries were subjected to discharge tests. The results showed that the self-discharge phenomenon of the primary batteries from Examples 2-5 was suppressed, the impedance was reduced, the discharge capacity was high, and the working voltage signal of the modified alloy negative electrode was smooth and stable.

[0078] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A surface modification method for a lithium alloy negative electrode of a primary lithium battery, characterized in that, Li-B alloys were modified with silver trifluoromethane mercaptan to form a surface layer containing metallic silver, LiF, and sulfides; the sulfides were Li-S. The surface modification method includes the following steps: Step 1: Dissolve silver trifluoromethane mercaptan in an organic solvent to prepare a reaction solution; Step 2: Select a bright Li-B alloy strip and cut it into Li-B alloy discs with a diameter of 16mm using a manual punching machine; Step 3: Place the Li-B alloy disc in the reaction solution from Step 1 and stir to perform thorough surface modification; Step 4: Clean and dry the alloy disc obtained in Step 3 to obtain a Li-B alloy with a surface rich in metallic silver, Li-F, and Li-S. The mass concentration of silver trifluoromethane mercaptan in the reaction solution is 0.5-10%.

2. The surface modification method for a primary lithium alloy negative electrode as described in claim 1, characterized in that, The organic solvent is any one or more of diethyl ether, tetrahydrofuran, ethylene glycol dimethyl ether, and dichloromethane.

3. The surface modification method for a primary lithium alloy negative electrode as described in claim 1, characterized in that, The organic solvent is tetrahydrofuran solvent.

4. The surface modification method for a primary lithium alloy negative electrode as described in claim 3, characterized in that, The tetrahydrofuran solvent is first dehydrated using a lithium-ionized molecular sieve for 24–72 hours.

5. The surface modification method for a primary lithium alloy negative electrode as described in claim 1, characterized in that, The stirring process conditions are a rotation speed of 300-600 rpm and a stirring time of 10-60 min.

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