A pre-lithiation method for a lithium-sulfur battery electrode and a lithium-sulfur battery

Abstract

This invention belongs to the technical field of lithium-sulfur batteries, and discloses a pre-lithiation method for lithium-sulfur battery electrodes and a lithium-sulfur battery. The positive electrode of the lithium-sulfur battery is a sulfur positive electrode. The pre-lithiation method includes: attaching a lithium foil to the surface of the positive electrode; assembling the positive electrode with the attached lithium foil to form a full cell; and allowing the full cell to stand to lithimate the positive electrode. This invention, by pre-lithiating the sulfur positive electrode, avoids introducing lithium sources into the negative electrode. Because the conductivity of the sulfur positive electrode is lower than that of the negative electrode, the heat release during contact with the lithium source is slower, which helps reduce safety hazards and improve safety performance. Using lithium foil to lithimate the positive electrode avoids the introduction of other substances, which helps ensure energy density and is suitable for battery systems lacking all lithium sources. Furthermore, the in-situ pre-lithiation method, where the lithium foil is attached to the positive electrode, eliminates the need for battery disassembly or other complex pre-lithiation operations, facilitating production line operations and commercial applications, thus demonstrating strong practicality.

Description

Technical Field

[0001] This invention belongs to the technical field of lithium-sulfur batteries, and more specifically, relates to a pre-lithiation method for lithium-sulfur battery electrodes and a lithium-sulfur battery. Background Technology

[0002] Lithium-sulfur batteries are secondary batteries that use sulfur or sulfur-carbon composite materials as the positive electrode, with a theoretical energy density of approximately 2600 Wh·kg⁻¹. -1 Sulfur is inexpensive and environmentally friendly, making lithium-sulfur batteries a popular choice for battery systems. However, lithium-sulfur batteries use lithium metal as the negative electrode, which introduces significant safety risks. Furthermore, side reactions between the lithium metal negative electrode and the electrolyte greatly reduce the cycle life of lithium-sulfur batteries. Currently, lithium-sulfur batteries are known for their high energy density, but their cycle life and safety are far from meeting the standards for commercially viable batteries.

[0003] To improve the cycle life and safety of lithium-sulfur batteries, the negative electrode can use carbon-based materials such as graphite and silicon-carbon that do not contain lithium metal, allowing lithium ions to be inserted and extracted within the negative electrode. These negative electrodes are then paired with sulfur positive electrodes to form a full cell. However, it is worth noting that this full cell lacks a lithium source; therefore, introducing a lithium source, i.e., pre-lithiation, is a key technology required for its normal operation.

[0004] Currently, the mainstream pre-lithiation methods include pre-lithiation of the negative electrode and pre-lithiation of the positive electrode. Negative electrode pre-lithiation includes physical mixing pre-lithiation, vacuum-wound lithium plating, electrochemical pre-lithiation, and chemical pre-lithiation. Among these, physical mixing pre-lithiation is the most widely used and commercially viable method. Physical mixing pre-lithiation involves directly pressing lithium metal onto the surface of a negative electrode such as graphite, or adding passivated lithium powder during the homogenization process. Positive electrode pre-lithiation mainly involves adding lithium-rich materials such as Li₂O and Li₃N during the positive electrode homogenization process. In practical operation, physical mixing pre-lithiation of the negative electrode still presents safety risks because carbon-based negative electrode materials such as graphite have good conductivity and release heat relatively quickly upon contact with lithium. Furthermore, the lithium-rich materials used in positive electrode pre-lithiation often introduce other substances. Therefore, lithium-rich materials are more suitable as supplementary lithium materials in battery systems lacking a partial lithium source. For battery systems lacking all lithium sources, more lithium-rich materials need to be added, which is not conducive to ensuring a high energy density for the battery system. In summary, there is still a lack of safe and effective pre-lithiation methods for lithium-sulfur battery systems with sulfur cathodes and graphite / silicon-carbon anodes. Summary of the Invention

[0005] In view of the above defects or improvement requirements of the prior art, the present invention provides a prelithiation method for lithium-sulfur battery electrodes and a lithium-sulfur battery, which solves the problem that there is a lack of safe and effective prelithiation methods in the existing full lithium-sulfur battery system with a sulfur positive electrode and negative electrodes such as graphite / silicon carbon materials, realizes in-situ prelithiation of the positive electrode through lithium foil, facilitates production line operation, has strong practicability and high safety.

[0006] To achieve the above object, according to one aspect of the present invention, there is provided a prelithiation method for a lithium-sulfur battery electrode, wherein the positive electrode of the lithium-sulfur battery is a sulfur positive electrode, and the prelithiation method comprises:

[0007] Laminating lithium foil on the surface of said positive electrode;

[0008] Assembling said positive electrode laminated with said lithium foil into a full battery;

[0009] Allowing said full battery to stand still to lithiate said positive electrode.

[0010] According to the prelithiation method for lithium-sulfur battery electrodes provided by the present invention, laminating lithium foil on the surface of said positive electrode specifically comprises:

[0011] Laminating lithium foil on the surface of said positive electrode on which active material is provided.

[0012] According to the prelithiation method for lithium-sulfur battery electrodes provided by the present invention, the thickness b of said lithium foil specifically satisfies: 3a < b < 7a; wherein a is the areal capacity per unit of said positive electrode, with a unit of mAh·cm -2 ; b is the thickness of said lithium foil, with a unit of um.

[0013] According to the prelithiation method for lithium-sulfur battery electrodes provided by the present invention, said prelithiation method further comprises:

[0014] Applying a preset pressure to said full battery for pressure treatment.

[0015] According to the prelithiation method for lithium-sulfur battery electrodes provided by the present invention, the value of said preset pressure is obtained through a test method, and said test method specifically is:

[0016] Preparing a test sample, wherein said test sample comprises two positive electrode samples, a lithium foil sample is arranged between the two said positive electrode samples, and electrolyte is respectively provided on the opposite faces of the two said positive electrode samples;

[0017] After applying a test pressure to said test sample in a vacuum environment and allowing it to stand for a preset time, acquiring the surface temperature of said positive electrode sample to perform a temperature collection test;

[0018] Adjusting said test pressure so that said test pressure presents an increasing trend to perform multiple groups of said temperature collection tests;

[0019] Based on the surface temperature of the positive electrode sample obtained from multiple temperature acquisition tests, when the surface temperature of the positive electrode sample reaches a preset temperature value, the test pressure in the corresponding temperature acquisition test is confirmed as the maximum value of the preset pressure.

[0020] The pre-lithiation method for lithium-sulfur battery electrodes provided by the present invention specifically includes the following steps for preparing test samples:

[0021] The electrolyte is applied to one surface of any of the aforementioned positive electrode samples.

[0022] The surfaces of the two positive electrode samples containing the electrolyte are attached to each other and the lithium foil sample is placed between the two positive electrode samples.

[0023] According to the pre-lithiation method for lithium-sulfur battery electrodes provided by the present invention, for any one of the said positive electrode samples, the wetting amount of the electrolyte is:

[0024] d≥2c, where c is the mass of the active material in the positive electrode sample in mg; and d is the amount of electrolyte added in μL.

[0025] According to the pre-lithiation method for lithium-sulfur battery electrodes provided by the present invention, the positive electrode is an organic sulfur positive electrode, a pure sulfur positive electrode, or a carbon-sulfur composite positive electrode; the negative electrode of the lithium-sulfur battery is a graphite negative electrode, a hard carbon negative electrode, a silicon-carbon negative electrode, a tin-carbon negative electrode, or a silicon negative electrode.

[0026] According to the pre-lithiation method for lithium-sulfur battery electrodes provided by the present invention, the ratio (NP ratio) of the areal capacity per unit area of ​​the negative electrode to the areal capacity per unit area of ​​the positive electrode of the lithium-sulfur battery is 0.8-2.

[0027] According to another aspect of the present invention, a lithium-sulfur battery is provided, which is prepared by the pre-lithiation method of the lithium-sulfur battery electrode described in any of the preceding claims.

[0028] In summary, compared with the prior art, the pre-lithiation method for lithium-sulfur battery electrodes and the lithium-sulfur battery provided by this invention offer the following advantages:

[0029] 1. By pre-lithiating the sulfur cathode, the introduction of lithium source into the anode can be avoided. Due to the low conductivity of the sulfur cathode, the heat release during contact with the lithium source is relatively slow, which helps to reduce safety hazards and improve safety performance. Using lithium foil to lithiate the cathode can avoid the introduction of other substances, which helps to ensure energy density and is suitable for battery systems that lack all lithium sources. In addition, the in-situ pre-lithiation method of attaching lithium foil to the cathode does not require disassembling the battery or other complex pre-lithiation operations, which is conducive to the formation of production line operations to achieve commercial applications and has strong practicality.

[0030] 2. The provided lithium foil thickness setting range is based on the lithium source requirements. Lithium foil within this thickness range can meet the battery's lithium source requirements without causing excessive lithium foil usage.

[0031] 3. The maximum value of the preset pressure can be obtained through multiple temperature acquisition tests. The preset pressure can be set according to this maximum value to pressurize the whole battery, which helps to accelerate the lithiation speed of the positive electrode and ensure safety performance. Attached Figure Description

[0032] Figure 1 This is a schematic flowchart of the pre-lithiation method for lithium-sulfur battery electrodes provided by the present invention.

[0033] Figure 2 The coin cell provided by this invention, which involves bonding lithium foil to the surface of a sulfurized polyacrylonitrile (SPAN) positive electrode and performing sufficient pre-lithiation, is paired with a graphite negative electrode and achieves a capacitance of 0.1 A·g. -1 The charge-discharge curves under the given current conditions;

[0034] Figure 3 In the comparative example, SPAN electrodes without attached lithium foil were assembled with lithium metal anodes to form a coin cell at 0.1 A·g. -1 The charge-discharge curves under the given current conditions;

[0035] Figure 4 The coin cell provided by this invention, which involves bonding lithium foil to the surface of a SPAN electrode for thorough pre-lithiation and then combining it with a graphite negative electrode, achieves a capacity of 0.5 A·g. -1 The cyclic curve of the current subjected to long-cycle testing;

[0036] Figure 5 In the comparative example, SPAN electrodes without attached lithium foil were assembled with lithium metal anodes to form a coin cell with a capacity of 0.5 A·g. -1 The cyclic curve of the current subjected to long-cycle testing;

[0037] Figure 6 The comparison involves a coin cell with lithium foil bonded to the surface of a graphite electrode and fully pre-lithiated, then combined with a SPAN electrode, achieving a capacitance of 0.5 A·g. -1 The cyclic curve of the current subjected to long-cycle testing;

[0038] Figure 7 The lithium foil provided by this invention is bonded to the surface of a SPAN electrode and fully pre-lithiated before being combined with graphite to form a coin cell with a capacity of 0.1 A·g. -1 The cyclic curve of the current subjected to long-cycle testing;

[0039] Figure 8 The lithium foil provided by this invention is fully pre-lithiated on the surface of a SPAN electrode and then combined with a commercial silicon-carbon anode to form a coin cell with a capacity of 0.1 A·g.-1 The current was subjected to a long-cycle test and the resulting cyclic curve was obtained. Detailed Implementation

[0040] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0041] Please see Figure 1 This invention provides a pre-lithiation method for a lithium-sulfur battery electrode, wherein the positive electrode of the lithium-sulfur battery is a sulfur positive electrode, and the pre-lithiation method includes:

[0042] S1, lithium foil is attached to the surface of the positive electrode;

[0043] S2, the positive electrode with the lithium foil attached is assembled to form a full battery;

[0044] S3, allow the full battery to stand to lithium-ionize the positive electrode.

[0045] This invention addresses the issue that most existing lithium-sulfur batteries use lithium metal as the negative electrode. The use of lithium metal negative electrodes poses significant safety risks to the battery system, and the side reactions between the lithium metal negative electrode and the electrolyte greatly reduce the cycle life of lithium-sulfur batteries. To improve the cycle life and safety of lithium-sulfur batteries, this invention provides a lithium-sulfur battery where the positive electrode is a sulfur positive electrode, and the negative electrode is an electrode that does not use lithium metal, such as a carbon-based negative electrode material like graphite. The electrode is then pre-lithiated to provide the lithium source required by the battery. Furthermore, this invention considers that even with pre-lithiation of the negative electrode, the high conductivity of carbon-based negative electrode materials like graphite still leads to rapid heat release during contact with lithium, posing a safety hazard. Therefore, this invention proposes pre-lithiating the sulfur positive electrode to ensure battery safety, improve energy density and cycle life, and facilitate the commercial application of lithium-sulfur batteries.

[0046] Specifically, compared with the existing commonly used method of adding lithium-rich materials such as Li₂O and Li₃N during the positive electrode homogenization process, the pre-lithiation method for sulfur positive electrode provided by the present invention directly adopts lithium foil to pre-lithiate the positive electrode, does not introduce other substances, which is conducive to ensuring the energy density of the battery. The method is not only suitable for lithium compensation of battery systems lacking part of lithium source, but also suitable for lithium compensation of battery systems lacking all lithium sources. Moreover, during the battery assembly process, it is only necessary to attach the lithium foil to the positive electrode sheet, and battery assembly can be performed after the lithium foil is attached to the positive electrode sheet. The lithiation of the positive electrode starts immediately after the lithium foil is attached to the positive electrode sheet, and sufficient lithiation of the positive electrode can be achieved through standing the full cell after the full cell is assembled, thereby realizing in-situ pre-lithiation of the sulfur positive electrode of a lithium-sulfur battery.

[0047] The pre-lithiation method for electrodes of lithium-sulfur batteries provided by the present invention can avoid introducing lithium source into the negative electrode by pre-lithiating the sulfur positive electrode. Due to the low electrical conductivity of the sulfur positive electrode, heat release is relatively slow during contact with the lithium source, which helps reduce safety hazards and improve safety performance; using lithium foil to lithiate the positive electrode can avoid introducing other substances, which is conducive to ensuring energy density and is suitable for battery systems lacking all lithium sources; in addition, the in-situ pre-lithiation method of attaching lithium foil to the positive electrode does not require battery disassembly or other complicated pre-lithiation operations, which is conducive to production line operation to realize commercial application, and has strong practicability.

[0048] Further, attaching the lithium foil to the surface of the positive electrode specifically includes: attaching the lithium foil to the surface of the positive electrode provided with active materials. In the present invention, pre-lithiation is performed by attaching lithium foil to the surface of the positive electrode where the active material is disposed. Specifically, when the active material is provided on one side of the positive electrode, lithium foil may be provided on the one side of the positive electrode; when the active material is provided on both sides of the positive electrode, lithium foil may be respectively provided on both sides of the positive electrode. This arrangement of lithium foil is conducive to faster and more uniform pre-lithiation of the positive electrode, ensuring the battery's demand for lithium source.

[0049] Further, the thickness b of the lithium foil specifically satisfies: 3a < b < 7a; wherein a is the areal capacity per unit of the positive electrode, whose unit is mAh·cm -2 ; b is the thickness of the lithium foil, whose unit is μm. The present invention provides a basis for selecting the thickness of lithium foil in this in-situ pre-lithiation method for positive electrodes. The thickness of the lithium foil is determined by the lithium source demand of the battery. The sulfur positive electrode provides all the lithium source required for the battery through pre-lithiation, so that the negative electrode does not need lithium compensation, which can improve safety performance. The lithium demand can be determined according to the areal capacity of the positive electrode, and the thickness of the lithium foil can be determined according to the lithium demand.

[0050] The lithium foil thickness setting range provided above is based on the lithium source requirements. Lithium foil within this thickness range can meet the battery's lithium source requirements without causing excessive lithium foil usage. If the lithium foil is too thin, the battery system will not receive enough lithium, resulting in a decrease in reversible capacity and overall energy density. If the lithium foil is too thick, it will lead to lithium waste and increase the battery's weight, thus reducing the overall energy density of the battery.

[0051] Furthermore, the thickness of the lithium foil is between 5µm and 300µm.

[0052] Furthermore, the area of ​​the lithium foil is greater than or equal to the area of ​​the positive electrode. The lithium foil should cover the positive electrode so that any part of the positive electrode can come into contact with the lithium foil for lithiation, thereby ensuring sufficient and uniform contact and lithiation between the positive electrode and the lithium foil.

[0053] Furthermore, the lithium foil can be directly attached to the positive electrode, or the lithium foil can be attached to the positive electrode and then fixed with tape or other means to ensure that the positive electrode and the lithium foil are in full contact, so as to facilitate battery assembly. There are no restrictions on whether additional fixing methods are used, or on the specific types of additional fixing methods.

[0054] Furthermore, the pre-lithiation method further includes: applying a preset pressure to the full battery for pressurization treatment. That is, when it is necessary to accelerate the lithiation speed, the battery can be pressurized. The pressurization treatment of the full battery can be performed after the full battery is assembled in S2. This pressurization process is beneficial to accelerate the lithiation speed of the positive electrode, achieve sufficient lithiation of the positive electrode, and ensure the lithiation effect. Furthermore, the pressurization treatment of the full battery can be performed by rolling, clamping with a clamping mechanism, or using atmospheric pressure, etc., and the specific pressurization method is not limited.

[0055] When the assembled full cell is pressurized, the pressure applied to the surface of the full cell is further transmitted to the positive electrode and the lithium foil, so that there is pressure between the positive electrode and the lithium foil, which is beneficial to accelerate the lithiation of the positive electrode and ensure the full lithiation of the positive electrode; and the pressurization of the full cell is convenient and easy to perform.

[0056] Furthermore, in other embodiments, when there is no requirement for the lithiation rate, it is not necessary to apply a preset pressure to the full battery for pressurization treatment.

[0057] Furthermore, when pressure needs to be applied, the value of the preset pressure is obtained through an experimental method, specifically:

[0058] Prepare a test sample, which includes two positive electrode samples, with a lithium foil sample between the two positive electrode samples, and an electrolyte is provided on the opposite surfaces of the two positive electrode samples; active material may be provided on the opposite surfaces of the two positive electrode samples.

[0059] After applying test pressure to the test sample in a vacuum environment and allowing it to stand for a preset time, the surface temperature of the positive electrode sample is obtained for temperature acquisition test.

[0060] Adjust the test pressure to make the test pressure increase in an incremental manner and perform multiple sets of temperature acquisition tests;

[0061] Based on the surface temperature of the positive electrode sample obtained from multiple temperature acquisition tests, when the surface temperature of the positive electrode sample reaches a preset temperature value, the test pressure in the corresponding temperature acquisition test is confirmed as the maximum value of the preset pressure.

[0062] This invention provides a method for obtaining a specific preset pressure value for pressurizing a full battery through experimentation. First, a test sample is prepared, comprising a positive electrode sample, a lithium foil sample, and an electrolyte. This test sample is consistent with the actual environment of the positive electrode and lithium foil during sulfur positive electrode pre-lithiation; that is, the lithium foil sample is in close contact with the positive electrode sample, and the surfaces of the lithium foil sample and the positive electrode sample in contact are in the electrolyte environment. This test sample can be used to verify the lithiation effect of the positive electrode through experimentation.

[0063] Specifically, this invention designs a temperature acquisition experiment. When the positive electrode and lithium foil undergo lithiation, a certain amount of heat is generated, causing the temperature of the test sample to rise. By acquiring the surface temperature of the positive electrode sample in the test sample, it can be observed that after the test sample is placed in a vacuum environment under pressure for a preset time, the surface temperature of the positive electrode sample will increase. Theoretically, the degree of surface temperature increase of the positive electrode sample will increase as the lithiation rate of the positive electrode accelerates.

[0064] Furthermore, multiple temperature acquisition tests can be conducted by changing the test pressure in the temperature acquisition test. Within a preset time, the rate of positive electrode lithiation is different under different test pressures. Therefore, the surface temperature of the positive electrode sample obtained under different test pressures is also different. It should be that as the test pressure increases, the rate of positive electrode lithiation increases, and the surface temperature of the positive electrode sample gradually increases.

[0065] This invention sets a safe temperature value for the surface of the positive electrode sample, namely a preset temperature value. When the surface temperature of the positive electrode sample is lower than the preset temperature value, the lithiation of the positive electrode sample and the lithium foil sample is within a safe range. However, if the surface temperature of the positive electrode sample is higher than the preset temperature value, it indicates that the lithiation rate is too high, which may cause certain safety hazards and damage to the material of the positive electrode sample. Therefore, the lithiation rate should be controlled to prevent it from becoming too high.

[0066] This invention proposes that when conducting multiple temperature acquisition tests, the surface temperature of the positive electrode sample gradually increases as the test pressure increases. When the surface temperature of the positive electrode sample increases to a preset temperature value, the corresponding test pressure in the temperature acquisition test is obtained, and this test pressure can be used as the maximum value of the preset pressure.

[0067] When actually pressurizing the full battery, the pressure applied to the full battery can be set to be less than or equal to the maximum value of the preset pressure to ensure that the lithiation rate of the positive electrode is not too high, so as to ensure safety and not damage the structure of the electrode.

[0068] Furthermore, the preset temperature can be 27-33℃. The preset time can be 3-10 minutes.

[0069] Furthermore, the preparation of test samples specifically includes:

[0070] The electrolyte is applied to one surface of any of the aforementioned positive electrode samples.

[0071] The surfaces of the two positive electrode samples containing the electrolyte are attached to each other and the lithium foil sample is placed between the two positive electrode samples.

[0072] This invention provides a specific method for preparing a test sample. First, an electrolyte is immersed in the surface of a positive electrode sample. Then, a lithium foil sample is attached between two positive electrode samples. The lithium foil sample is positioned between the surfaces of the two positive electrode samples, each immersed in the electrolyte, thereby placing the lithium foil sample in an electrolyte environment where it undergoes lithiation with the positive electrode samples, consistent with the actual lithiation environment of the positive electrode. Furthermore, an active material is provided on the surface of each positive electrode sample immersed in the electrolyte.

[0073] Furthermore, the specific operation of wetting the surface of the positive electrode sample with electrolyte can be as follows: drop a preset amount of electrolyte onto the surface of the positive electrode sample, so that the electrolyte covers the entire surface of the positive electrode sample.

[0074] Furthermore, for any one of the aforementioned positive electrode samples, the amount of electrolyte wetting is:

[0075] d≥2c, where c is the mass of the active material in the positive electrode sample (mg), and d is the amount of electrolyte added (µL). This invention also provides a specific amount of electrolyte to be taken when immersing the positive electrode sample in electrolyte. Electrolyte droplets within this range can ensure that the surface of the positive electrode sample is fully covered, allowing the active material on the surface of the positive electrode sample to be fully immersed in the electrolyte.

[0076] Further, when it is necessary to accelerate the lithiation speed, the acquisition of the preset pressure further comprises: setting the preset pressure according to the material properties of the positive electrode, so that the material properties of the positive electrode of the full battery remain stable under the preset pressure. That is, when applying pressure treatment to the full battery, a larger preset pressure is not necessarily better, and it should be ensured that the positive electrode is not damaged.

[0077] Optionally, the pressure range adjusted by the preset pressure is 0MPa-50 MPa. Performing pressure treatment on the full battery with the preset pressure within this value range is beneficial to increasing the lithiation speed of the positive electrode, ensuring full lithiation of the positive electrode, and will not damage the battery.

[0078] Further, the positive electrode is an organic sulfur positive electrode, a pure sulfur positive electrode or a carbon-sulfur composite positive electrode; the negative electrode of the lithium-sulfur battery is a graphite negative electrode, a hard carbon negative electrode, a silicon-carbon negative electrode, a tin-carbon negative electrode or a silicon negative electrode. Preferably, the positive electrode is a SPAN positive electrode, and the negative electrode is a graphite negative electrode.

[0079] Further, the NP ratio of the battery is 0.8-2.

[0080] Further, the present invention also provides a lithium-sulfur battery, which is prepared by any one of the above prelithiation methods for electrodes of lithium-sulfur batteries. That is, when the lithium-sulfur battery is prepared, a lithium foil is attached to the surface of the positive electrode, and the lithium-sulfur battery is assembled after attaching the lithium foil; the sulfur positive electrode of the lithium-sulfur battery is lithiated by means of in-situ prelithiation.

[0081] Further, aiming at the existing technical defects, the present invention provides a prelithiation method for a sulfur positive electrode of a lithium-sulfur battery, in which a thin lithium foil is attached to the surface of a sulfur positive electrode plate and then the battery is assembled to achieve in-situ prelithiation, and the introduction of a lithium source for a lithium-sulfur full battery is realized by the method of prelithiating the sulfur positive electrode.

[0082] Specifically, the present invention adopts the following technical solution: preparing an ultra-thin lithium foil, the thickness of the lithium foil is in the range of 5um-300um; the purity of the lithium foil is greater than 90%, preferably greater than 99.5%; the required thickness of the lithium foil is determined according to the areal capacity of the positive electrode, assuming that the areal capacity of the positive electrode is a, whose unit is mAh·cm -2 , the thickness of the lithium foil is b, whose unit is um, then 3a<b<7a, for example, optionally b=5a; the positive electrode is a SPAN positive electrode or other organic sulfur positive electrode, pure sulfur positive electrode, or carbon-sulfur composite positive electrode; the negative electrode is a graphite negative electrode, a hard carbon negative electrode, a silicon-carbon negative electrode, a tin-carbon negative electrode or a silicon negative electrode; the NP ratio of the battery is 0.8-2; when assembling the battery, after attaching the lithium foil to the surface of the positive electrode plate, assemble it directly into a full battery. The area of the lithium foil is slightly larger than the area of the positive electrode plate to ensure that the positive electrode active material is in full contact with the lithium foil.

[0083] For button cells, the lithium foil can be placed directly on the surface of the positive electrode without special fixing. For pouch cells, the lithium foil can be fixed with tape or by machine alignment after it is attached to the positive electrode. After assembling the battery, appropriate pressure needs to be applied to ensure full lithiation within a specified time. The applied pressure should not exceed 50 MPa, preferably not exceeding 10 MPa. After the full battery is assembled, let it stand to allow the positive electrode to be fully lithiated by the lithium foil before charging and discharging tests and long-cycle tests are performed.

[0084] This in-situ pre-lithiation method eliminates the need for battery disassembly or other complex pre-processing, facilitating production line operation and commercialization. Furthermore, using lithium foil as the lithium source avoids the introduction of other substances. It is worth noting that the conductivity of the sulfur cathode is lower than that of carbon-based anodes such as graphite, resulting in a relatively slow heat release during contact with the lithium foil, thus reducing safety hazards.

[0085] To make the implementation scheme and effects of the present invention clearer, the present invention will be further explained below with reference to specific embodiments.

[0086] Example 1:

[0087] In this embodiment, lithium foil is bonded to the surface of the SPAN electrode, that is, SPAN is used as the positive electrode, and the positive electrode is pre-lithiated as described in the above embodiments.

[0088] The SPAN positive electrode sheet is made by mixing the active material SPAN, conductive carbon black Super P, and water-based binder LA133 in a ratio of 8:1:1. The SPAN loading in the electrode sheet is controlled at 3.8-4.2 mg·cm³. -2 Within the specified range. In an argon-filled glove box, two SPAN electrodes with a 20µm lithium foil sandwiched between them were used. An ester-based electrolyte (model LB-015) was added. The amount of electrolyte added needs to be determined based on the electrode area. Assuming the mass of the active material on the electrode is c (mg) and the amount of electrolyte added is d (µL), then d ≥ 2c. Infrared thermal imaging of the electrode surface immediately after adding the electrolyte showed that the temperature of most areas was around 13.8℃.

[0089] When pressure is applied to the lithium foil and electrode using a clamp, and after the electrode and lithium foil have made full contact and the electrolyte has fully wetted them (approximately 5 minutes), infrared thermal imaging of the electrode is performed again. It can be seen that as SPAN pre-lithiation proceeds, the temperature increases to a certain extent, reaching a local temperature of 16.6℃. This experiment also demonstrates that applying appropriate pressure after the electrode is bonded to the lithium foil is beneficial for ensuring sufficient lithiation of the electrode within the specified time. Experimental measurements show that insufficient pressure will lead to incomplete lithiation of the electrode within the specified time, while excessive pressure will cause the electrode temperature to become too high or even deform and be damaged. Therefore, for the positive electrode bonding method used in this invention, the pressure applied after bonding needs to be no greater than 50 MPa, preferably no greater than 10 MPa.

[0090] Comparative Example 1:

[0091] This comparative example uses lithium foil bonded to the surface of a graphite electrode, that is, the graphite anode is pre-lithiated using the pre-lithiation method described in the above embodiments.

[0092] The graphite electrode is made of artificial graphite, conductive carbon black Super P, carboxymethyl cellulose (CMC) binder, and styrene-butadiene rubber (SBR) binder in a ratio of 90:5:2.5:2.5. The graphite loading in the electrode is controlled at 9.8-10.2 mg·cm³. -2 Within the specified range, in an argon-filled glove box, two graphite electrodes with a 20µm lithium foil sandwiched between them were used. LB-015 electrolyte was added, and infrared thermal imaging was performed. It was observed that the temperature in most areas was around 14.8°C. After applying pressure with a fixture for 5 minutes, infrared thermal imaging was performed again, revealing that the temperature reached over 20°C as graphite pre-lithiation progressed. Compared to Example 1, Comparative Example 1 generated more heat in a shorter time. This is related to the higher electronic conductivity of graphite compared to SPAN. The rapid heat release from the excessively rapid lithiation reaction poses certain safety hazards to battery production.

[0093] Example 2:

[0094] In this embodiment, a coin cell with a graphite negative electrode is used after being fully pre-lithiated by bonding lithium foil to the surface of the SPAN electrode.

[0095] The SPAN positive electrode sheet was prepared according to the method in Example 1. In an argon-filled glove box, a 20µm lithium foil was bonded to the positive electrode surface, and then assembled into a coin cell with a graphite negative electrode. The preparation method of the graphite electrode sheet was the same as in Comparative Example 1, and LB-015 electrolyte was used. The battery was allowed to stand for 12 hours before charge-discharge testing. Since the positive electrode underwent sufficient pre-lithiation, the battery was first charged at 0.1 A·g. -1The battery was charged to 3.4V under specified current conditions to ensure reversible lithium distribution from the positive electrode to the graphite negative electrode. It was then cycled twice within a voltage range of 1-3V. The battery charge-discharge curve is shown below. Figure 2 As shown, during the first discharge, the battery did not exhibit more polarization than the second discharge curve, and the discharge curve was consistent with the subsequent discharge. This indicates that after in-situ pre-lithiation, SPAN has formed a solid electrolyte interface (CEI) film, and lithium ions are embedded in the positive electrode skeleton, improving the overall conductivity of the electrode and thus reducing the polarization caused by the first lithium intercalation of the positive electrode.

[0096] Comparative Example 2:

[0097] This comparative example uses SPAN electrodes without attached lithium foil to assemble a coin cell with a lithium metal negative electrode for charge and discharge testing.

[0098] The SPAN positive electrode was prepared according to Example 1, and assembled into a lithium coin cell in an argon-filled glove box. LB-015 electrolyte was used. The electrolyte concentration was 0.1 A·g within a voltage range of 1-3V. -1 Under the specified current conditions, the battery was subjected to charge-discharge tests. For example... Figure 3 As shown, during the first discharge of the battery, due to the lack of pre-lithiation of the SPAN positive electrode, no CEI was formed and the conductivity was poor, resulting in significant polarization. The initial discharge requires additional lithium ions to lithimate the positive electrode, thus the initial discharge capacity is higher than that of subsequent discharges. These lithium ions irreversibly embed into the positive electrode framework, improving the conductivity of the positive electrode and reducing polarization during subsequent discharges.

[0099] Example 3:

[0100] This embodiment uses a coin cell with a graphite negative electrode after sufficient pre-lithiation by bonding lithium foil to the surface of a SPAN electrode. The desired result is 0.5 A·g. -1 The current was subjected to long-cycle testing.

[0101] The button cell was assembled using the method described in Example 2. After the cell was left to stand for 12 hours, it was tested at 0.5 A·g. -1 Long-cycle testing was performed under the specified current conditions. For example... Figure 4 As shown, after SPAN is matched with graphite anode, the specific capacity will decrease when discharged to 1V due to the overpotential of graphite lithium intercalation. However, since there is no lithium metal formation, the rapid capacity decay caused by the side reaction between lithium metal and electrolyte is avoided, and the cycle stability is improved. Through experiments, the battery can still cycle stably when cycled to 10,000 times.

[0102] Comparative Example 3-1:

[0103] This comparative example uses SPAN electrodes without attached lithium foil to assemble a coin cell with a lithium metal negative electrode at a capacity of 0.5 A·g. -1 The current was subjected to long-cycle testing.

[0104] The battery was assembled using the method described in Comparative Example 2. After being left to stand for 12 hours, the battery was tested at 0.5 A·g. -1 Long-cycle testing was performed under the specified current conditions. For example... Figure 5 As shown, due to the use of lithium metal, the side reactions between lithium metal and electrolyte lead to poor battery cycle stability, and the capacity decays rapidly in less than 200 cycles.

[0105] Comparative Example 3-2:

[0106] This comparative example uses lithium foil bonded to the surface of graphite electrodes for thorough pre-lithiation, followed by a coin cell with a SPAN electrode, achieving a capacitance of 0.5 A·g. -1 The current was subjected to long-cycle testing.

[0107] SPAN positive electrode and graphite negative electrode were prepared according to Example 1. In an argon-filled glove box, 20µm lithium foil was bonded to the surface of the graphite negative electrode, which was then assembled with the SPAN positive electrode to form a coin cell. LB-015 electrolyte was used. After the battery was allowed to stand for 12 hours, it was charged at 0.5 A·g. -1 The current is subjected to long-cycle testing. For example... Figure 6 As shown, the cycle stability of the battery is lower than that of Example 3. Experimental observations indicate that due to the different ways lithium ions are intercalated in the positive and negative electrodes, the volume expansion direction of the lithium-intercalated graphite is perpendicular to the electrode surface. Therefore, when lithium foil is attached to the graphite electrode, it easily leads to powder shedding from the graphite electrode, causing the active material to detach and resulting in capacity decay. Consequently, the specific capacity and cycle stability are lower than those of Example 3. In contrast, during the lithiation process of the positive electrode, the volume expansion diffuses outwards, and the active material basically does not detach, thus exhibiting higher stability.

[0108] Example 4:

[0109] This embodiment uses a coin cell with a graphite negative electrode after sufficient pre-lithiation by bonding lithium foil to the surface of a SPAN electrode. The desired result is 0.1 A·g. -1 The current was subjected to long-cycle testing.

[0110] The button cell was assembled using the method described in Example 2. After the cell was left to stand for 12 hours, its performance was 0.1 A·g. -1 Long-cycle testing was performed under the specified current conditions. For example... Figure 7 As shown, it can be seen that the full cell can still cycle stably under low current density conditions. Through experiments, the battery can still cycle stably even after 10,000 cycles.

[0111] Comparative Example 4:

[0112] This comparative example uses lithium foil bonded to the surface of a SPAN electrode for thorough pre-lithiation, followed by pairing with a commercially available silicon-carbon anode in a coin cell at 0.1 A·g. -1 The current was subjected to long-cycle testing.

[0113] The SPAN positive electrode was prepared according to Example 1. A 20µm lithium foil was bonded to the SPAN positive electrode surface in an argon-filled glove box, and then assembled into a coin cell with a commercial silicon-carbon negative electrode. The commercial silicon-carbon negative electrode was purchased from KELU Corporation, and LB-015 electrolyte was used. After the battery was allowed to stand for 12 hours, the electrolyte concentration was 0.1 A·g. -1 Long-cycle testing was performed under the specified current conditions. For example... Figure 8 As shown, it can be seen that due to the large volume change of the silicon-carbon anode during charging and discharging, the electrode structure is more severely damaged during cycling than that of the graphite anode, and the capacity decay is faster than that of the graphite anode.

[0114] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements 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 method for pre-lithiation of a lithium-sulfur battery electrode, characterized in that, The positive electrode of the lithium-sulfur battery is a sulfur positive electrode, and the pre-lithiation method includes: A lithium foil is attached to the surface of the positive electrode; The positive electrode, on which the lithium foil is attached, is assembled with the negative electrode of the lithium-sulfur battery to form a full cell; the negative electrode of the lithium-sulfur battery is a graphite negative electrode, a hard carbon negative electrode, a silicon-carbon negative electrode, a tin-carbon negative electrode, or a silicon negative electrode; The positive electrode is lithium-ionized by allowing the full battery to stand. Specifically, attaching lithium foil to the surface of the positive electrode includes: A lithium foil is attached to the surface of the positive electrode where an active material is disposed. The pre-lithiation method further includes: A preset pressure is applied to the full battery to accelerate the lithiation rate of the positive electrode; The value of the preset pressure is obtained through an experimental method, which specifically includes: Prepare a test sample, which includes two positive electrode samples, with a lithium foil sample between the two positive electrode samples, and electrolyte is provided on the opposite surfaces of the two positive electrode samples; After applying test pressure to the test sample in a vacuum environment and allowing it to stand for a preset time, the surface temperature of the positive electrode sample is obtained for temperature acquisition test. Adjust the test pressure to make the test pressure increase in an incremental manner and perform multiple sets of temperature acquisition tests; Based on the surface temperature of the positive electrode sample obtained from multiple temperature acquisition tests, when the surface temperature of the positive electrode sample reaches a preset temperature value, the test pressure in the corresponding temperature acquisition test is confirmed as the maximum value of the preset pressure; the preset temperature value is the safe temperature value of the surface of the positive electrode sample.

2. The pre-lithiation method for lithium-sulfur battery electrodes as described in claim 1, characterized in that, The thickness b of the lithium foil is specifically: 3a<b<7a; wherein, a is the areal capacity of the positive electrode, with a unit of mAh·cm 2 ; b is the thickness of the lithium foil, with a unit of μm.

3. The pre-lithiation method for lithium-sulfur battery electrodes as described in claim 1, characterized in that, The preparation of test samples specifically includes: The electrolyte is applied to one surface of any of the aforementioned positive electrode samples. The surfaces of the two positive electrode samples containing the electrolyte are attached to each other and the lithium foil sample is placed between the two positive electrode samples.

4. The pre-lithiation method for lithium-sulfur battery electrodes as described in claim 3, characterized in that, For any of the aforementioned positive electrode samples, the amount of electrolyte wetting is: d≥2c, where c is the mass of the active material in the positive electrode sample in mg; and d is the amount of electrolyte added in μL.

5. The pre-lithiation method for lithium-sulfur battery electrodes according to any one of claims 1-3, characterized in that, The cathode is an organic sulfur cathode, a pure sulfur cathode, or a carbon-sulfur composite cathode.

6. The pre-lithiation method for lithium-sulfur battery electrodes according to any one of claims 1-3, characterized in that, The ratio (NP ratio) of the areal capacity per unit area of ​​the negative electrode to the areal capacity per unit area of ​​the positive electrode in the lithium-sulfur battery is 0.

8.

2.

7. A lithium-sulfur battery, characterized in that, The lithium-sulfur battery electrode is prepared by the pre-lithiation method according to any one of claims 1-6.

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