Ceramic composite lithium supplementing diaphragm as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of lithium ion batteries, and particularly relates to a ceramic composite lithium supplementing diaphragm and a preparation method and application thereof.The preparation method comprises the following steps that a cobalt source is dissolved in ethylene glycol, polyvinylpyrrolidone and a first sulfur source are added, and a solid precursor is obtained; calcining the solid precursor in a protective atmosphere, mixing the solid precursor with a second sulfur source, transferring the mixture into a closed container, and calcining to obtain a composite material; dispersing the composite material, conductive carbon black and PVDF in a solvent, grinding into slurry, coating a diaphragm with the slurry, and drying to obtain a CSP diaphragm; and dropwise adding electrolyte on the surface of the CSP diaphragm, and then covering the CSP diaphragm with a lithium sheet for in-situ lithiation to obtain the LCSP diaphragm. Compared with the prior art, the problems of complex process and expensive raw materials in the prior art are solved. According to the scheme, the method is simple in preparation process, large-scale production can be further achieved in a roll-to-roll mode, the whole manufacturing process of the diaphragm completely adapts to the production process of the lithium ion battery, and the production cost is reduced.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium-ion batteries, and in particular relates to a ceramic composite lithium-supplementing diaphragm and a preparation method and application thereof. Background Art

[0002] Lithium-ion batteries have been widely used in energy storage grids, portable electronics, and electric vehicles.

[0003] Commercial lithium-ion batteries are typically composed of a lithium-containing transition metal oxide positive electrode (lithium cobalt oxide, lithium iron phosphate, and ternary materials, etc.) and a lithium-poor negative electrode (mainly graphite). During the first cycle of charging, the electrolyte undergoes an irreversible electrochemical reduction reaction, forming a SEI film on the surface of the negative electrode. In this process, 5-20% of the active lithium ions in the positive electrode are usually consumed, resulting in a decrease in the first cycle coulombic efficiency and a decrease in battery capacity. In order to compensate for this capacity loss, it is necessary to supplement the electrodes with additional active lithium ions before battery assembly.

[0004] Lithium replenishment methods can be divided into negative electrode lithium replenishment and positive electrode lithium replenishment, among which the negative electrode lithium replenishment methods mainly include chemical lithiation and electrochemical lithiation. Metal lithium foil or stabilized lithium metal powder is directly contacted with the negative electrode or the negative electrode is immersed in a reducing lithium-containing solution, and a part of the lithium ions are pre-embedded into the negative electrode through in-situ chemical reaction, thereby compensating for the loss of capacity. However, the degree of pre-lithiation with this method is difficult to control, and excessive lithium replenishment will cause lithium deposition in the battery, causing safety hazards. The degree of pre-lithiation can be precisely controlled by the electrochemical pre-embedding method, but the operation process requires assembly and disassembly of the battery, and the process is relatively complicated and not suitable for commercial mass production. Another method is to replenish lithium on the positive electrode side, such as using over-lithiated positive electrode materials (Li5V2(PO4)3, Li 1+x Ni 0.5 Mn 1.5 During the first charge, additional lithium ions are released from the positive electrode to compensate for the lithium ion consumption by the SEI film. However, these materials have limited lithium replenishment capacity, and their high voltage platform can easily cause electrolyte decomposition, which is not conducive to the stable cycle of the battery.

[0005] The introduction of lithium-supplementing additives is currently a relatively feasible solution. Its lithium-supplementing capacity can be controlled by adjusting the additive content, and the additive can be directly mixed with the positive electrode material, making the preparation process simple. In addition, positive electrode lithium-supplementing additives are usually low-cost and have good chemical stability, making them suitable for large-scale commercial applications. The ideal lithium-supplementing additive needs to have a lithium storage capacity far higher than that of the positive electrode material, its delithiation potential should be lower than the maximum charge potential of the positive electrode, and it should no longer insert lithium within the positive electrode discharge voltage range. Specifically, the lithium-supplementing agent should remain electrochemically inert after delithiation and should not affect the subsequent cycles of the battery.

[0006] However, current lithium-supplementing additives typically become poor conductors of lithium ions and electrons after de-lithiation. When introduced into the positive electrode, this reduces the overall conductivity of the electrode, hindering the subsequent battery capacity. Applying lithium-supplementing additives to the separator can address this issue. Furthermore, as an inorganic coating, they can improve the separator's electrolyte wettability, thereby reducing interfacial impedance.

[0007] In the existing technology, such as CN119651057A (a lithium-replenishing diaphragm and its preparation method, lithium-ion battery), CN114552125B (a lossless lithium-replenishing composite diaphragm and its preparation method and application) and CN117936757B (a lithium-replenishing material, a lithium-replenishing diaphragm and its preparation method), relevant research has been conducted on lithium-replenishing diaphragms. However, the solutions adopted in the existing technology have problems such as complex processes and expensive raw materials, which make it difficult for lithium-replenishing diaphragms to be effectively applied in actual production. Summary of the Invention

[0008] The present invention aims to address at least one of the aforementioned issues by providing a ceramic composite lithium-replenishing separator, its preparation method, and its application, addressing the complex processes and expensive raw materials inherent in the prior art. This approach involves modifying the separator with a lithium-replenishing agent, designed to compensate for the initial capacity loss of the battery. This method offers a simple preparation process and can be further scaled up via a roll-to-roll process. The entire separator manufacturing process is fully compatible with current lithium-ion battery production processes, significantly reducing production costs and demonstrating promising prospects for practical application.

[0009] The purpose of the present invention is achieved through the following technical solutions:

[0010] The first aspect of the present invention discloses a method for preparing a ceramic composite lithium-supplementing separator, comprising the following steps:

[0011] S1: Preparation of CoS2 / Co3S4 composite materials:

[0012] A cobalt source is dissolved in ethylene glycol, and then polyvinyl pyrrolidone and a first sulfur source are added to react to obtain a solid precursor; the solid precursor is calcined under a protective atmosphere, and the black powder obtained after calcination is mixed with a second sulfur source, and then transferred to a closed container for calcination to perform sulfurization to obtain a CoS2 / Co3S4 composite material;

[0013] S2: Preparation of CSP diaphragm:

[0014] The CoS2 / Co3S4 composite material, conductive carbon black and PVDF are dispersed in an organic solvent and ground to form a slurry, which is then coated on a diaphragm and dried to obtain a CSP diaphragm.

[0015] S3: Preparation of LCSP membrane:

[0016] After adding electrolyte to the surface of the CSP diaphragm, a lithium sheet is placed on it. The CSP diaphragm is pressurized by the lithium sheet to perform in-situ lithiation to obtain an LCSP diaphragm.

[0017] Preferably, step S1 includes one or more of the following:

[0018] i) the cobalt source is one or more of anhydrous cobalt acetate, anhydrous cobalt sulfate, anhydrous cobalt nitrate, anhydrous cobalt carbonate, cobalt naphthenate, anhydrous cobalt chloride, anhydrous cobalt bromide, cobalt boroacylate and cobalt citrate;

[0019] ii) the first sulfur source is thiourea;

[0020] iii) the mass ratio of the cobalt source, polyvinyl pyrrolidone and the first sulfur source is 6-10:8-12:1-10;

[0021] iv) the second sulfur source is sulfur powder;

[0022] v) The mass ratio of the black powder to the second sulfur source is 1 to 6:1.

[0023] Preferably, step S1 includes one or more of the following:

[0024] i) ethylene glycol containing a cobalt source, polyvinyl pyrrolidone and thiourea are subjected to condensation reflux reaction at 120-180° C. for 2-6 hours;

[0025] ii) The solid precursor was heated at 1-5°C·min in an argon atmosphere. -1 The temperature is raised to 800°C at a rate of 100°C and kept at this temperature for 1 to 6 hours;

[0026] iii) The mixture of the black powder and the sulfur powder is sulfurized at 200-500° C. for 1-6 hours under an argon atmosphere.

[0027] Preferably, in step S1, after the sulfurization is completed, the sealed state of the closed container is released, and calcination is continued to completely volatilize excess sulfur.

[0028] Preferably, after the vulcanization is completed, the sealed state of the sealed container is released, and calcination is continued at 200-500° C. for 1-6 hours to completely volatilize excess sulfur.

[0029] Preferably, step S2 includes one or more of the following:

[0030] i) the conductive carbon black is Super P;

[0031] ii) the mass ratio of the CoS2 / Co3S4 composite material, the conductive carbon black and the PVDF is 4-8:1-3:1-3;

[0032] iii) the organic solvent is NMP;

[0033] iv) The separator is a PP separator.

[0034] Preferably, in step S3, the in-situ lithiation is: pressurizing the lithium sheet covering the surface of the CSP diaphragm to cause lithiation of the CSP diaphragm, and the duration of the lithiation process is within 45 seconds.

[0035] The second aspect of the present invention discloses a ceramic composite lithium-supplementing separator, which is prepared by any of the above methods.

[0036] The third aspect of the present invention discloses an application of the ceramic composite lithium-supplementing separator described above in a lithium-ion battery.

[0037] Preferably,

[0038] When the ceramic composite lithium-supplementing diaphragm is assembled in a half-cell, the half-cell is formed by pressing a positive electrode shell, a positive electrode sheet, a ceramic composite lithium-supplementing diaphragm, a lithium sheet, nickel foam and a negative electrode shell, wherein an electrolyte is dripped on the surface of the ceramic composite lithium-supplementing diaphragm;

[0039] When the ceramic composite lithium-supplementing diaphragm is assembled in a full battery, the full battery is pressed and formed by a positive electrode shell, a positive electrode plate, a ceramic composite lithium-supplementing diaphragm, a negative electrode plate, a stainless steel sheet, nickel foam and a negative electrode shell, wherein an electrolyte is dripped on the surface of the ceramic composite lithium-supplementing diaphragm.

[0040] Preferably, the half-cell is a lithium iron phosphate|Li half-cell or a graphite half-cell; and the full cell is a lithium iron phosphate|graphite full cell.

[0041] The working principle of the present invention is:

[0042] A CoS2 / Co3S4 composite material was synthesized using a simple condensation reflux method. This material exhibits high lithium storage capacity and good structural stability. Super P was then added to the mixture to form carbon-coated CoS2 / Co3S4 composite nanoparticles. This highly conductive nanostructure accelerates the lithiation reaction rate and increases the degree of lithiation. The resulting CoS2 / Co3S4 composite material retains its nanostructure, allowing lithium ions to be released more rapidly during charging, contributing to greater battery capacity. The carbon-coated CoS2 / Co3S4 composite nanoparticles were then modified onto a commercial PP separator via slurry coating, using a manufacturing process compatible with current lithium-ion battery production processes.

[0043] Compared with the prior art, the present invention has the following beneficial effects:

[0044] This approach synthesizes carbon-coated CoS2 / Co3S4 nanoparticles (a CoS2 / Co3S4 composite material coated with conductive carbon black) by condensation reflux followed by high-temperature sintering. These nanoparticles are then coated onto a commercial PP separator and, through in-situ lithiation, are used to create a Li2S / Co lithium-supplementing separator (LCSP). The manufacturing process for this functional separator is compatible with current lithium-ion battery production processes, making it an ideal industrial lithium-supplementing method.

[0045] The LCSP separator is fully lithiated in just 45 seconds, and the Li2S / Co coating formed after lithiation has a high lithium replenishment capacity (993 mA·h·g -1 ), the degree of lithium replenishment can be precisely controlled by adjusting the loading of the lithium replenishment coating.

[0046] LCSP separator can significantly improve the specific capacity of lithium iron phosphate / graphite batteries, and the energy density is also improved accordingly. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Figure 1 XRD patterns of (a) CoS2 / Co3S4 composite material and (b) Li2S / Co product.

[0048] Figure 2 SEM images of the coating surfaces of (a, b) CSP diaphragm and (c, d) LCSP diaphragm.

[0049] Figure 3 Specific capacity diagram of negative electrode half-cell assembled with LCSP separator, CSP separator, and PP separator.

[0050] Figure 4 Cross-sectional SEM images of (ac) CSP membrane and (df) LCSP membrane and the corresponding element distribution maps.

[0051] Figure 5 (a) The cycling performance of the lithium iron phosphate positive electrode at 0.5C and (b) the charge and discharge curve; (c) The cycling performance of the graphite negative electrode at 0.5C and (d) the first cycle charge and discharge curve.

[0052] Figure 6 These are the first cycle charge and discharge curves of graphite, lithium iron phosphate half-cells and full cells (the battery capacity is normalized based on the specific capacity of lithium iron phosphate being 1).

[0053] Figure 7 These are the first cycle charge and discharge curves of LiFePO4|graphite full batteries using different separators.

[0054] Figure 8 (a) Cycling performance of LiFePO4|graphite full batteries with different separators; charge and discharge curves of full batteries assembled with (b) PP separator and (c) LCSP separator at different cycles.

[0055] Figure 9 Specific capacity and energy density of two types of membrane batteries. DETAILED DESCRIPTION

[0056] The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0057] In the following description, unless otherwise specified, the reagents used are conventional commercial products, the methods used are well known in the art, and other matters not mentioned are prior art.

[0058] A method for preparing a ceramic composite lithium-supplementing diaphragm comprises the following steps:

[0059] S1: Preparation of CoS2 / Co3S4 composite materials:

[0060] A cobalt source is dissolved in ethylene glycol, and then polyvinyl pyrrolidone and a first sulfur source are added to react to obtain a solid precursor; the solid precursor is calcined under a protective atmosphere, and the black powder obtained after calcination is mixed with a second sulfur source, and then transferred to a closed container for calcination to perform sulfurization to obtain a CoS2 / Co3S4 composite material;

[0061] S2: Preparation of CSP diaphragm:

[0062] The CoS2 / Co3S4 composite material, conductive carbon black and PVDF are dispersed in an organic solvent and ground to form a slurry, which is then coated on a diaphragm and dried to obtain a CSP diaphragm.

[0063] S3: Preparation of LCSP membrane:

[0064] After adding electrolyte to the surface of the CSP diaphragm, a lithium sheet is placed on it. The CSP diaphragm is pressurized by the lithium sheet to perform in-situ lithiation to obtain an LCSP diaphragm.

[0065] in,

[0066] In step S1:

[0067] The cobalt source is one or more of anhydrous cobalt acetate, anhydrous cobalt sulfate, anhydrous cobalt nitrate, anhydrous cobalt carbonate, cobalt naphthenate, anhydrous cobalt chloride, anhydrous cobalt bromide, cobalt boroacylate and cobalt citrate; further, the cobalt source is preferably anhydrous cobalt acetate;

[0068] The first sulfur source is thiourea;

[0069] The mass ratio of the cobalt source, polyvinyl pyrrolidone and the first sulfur source is 6-10:8-12:1-10; further, the mass ratio is 8:10.8:8;

[0070] The second sulfur source is sulfur powder;

[0071] The mass ratio of the black powder to the second sulfur source is 1 to 6:1; further, the mass ratio is 3:1;

[0072] Ethylene glycol, polyvinyl pyrrolidone and thiourea dissolved with a cobalt source are subjected to condensation reflux reaction at 120-180° C. for 2-6 hours; further, the reaction is carried out at 150° C. for 4 hours;

[0073] The solid precursor was heated at 1-5℃·min in argon atmosphere. -1 The temperature was raised to 800℃ at a rate of 1-6h and kept at that temperature for 1-6h; further, the temperature was raised to 800℃ at a rate of 2℃·min -1 The temperature was raised to 800℃ at a rate of 1000℃ and kept at this temperature for 2h;

[0074] The mixture of black powder and sulfur powder is sulfurized at 200-500° C. for 1-6 hours under an argon atmosphere; further, it is sulfurized at 300° C. for 2 hours.

[0075] In step S1, after the vulcanization is completed, the sealed state of the closed container is released, and calcination is continued to completely volatilize excess sulfur. Specifically, after the vulcanization is completed, the sealed state of the closed container is released, and calcination is continued at 200-500° C. for 1-6 hours to completely volatilize excess sulfur. Further, calcination is performed at 300° C. for 2 hours.

[0076] In step S2:

[0077] The conductive carbon black is Super P;

[0078] The mass ratio of the CoS2 / Co3S4 composite material, the conductive carbon black and the PVDF is 4-8:1-3:1-3; further, the mass ratio is 7:2:1;

[0079] The organic solvent is NMP;

[0080] The diaphragm is a PP diaphragm.

[0081] In step S3:

[0082] In-situ lithiation involves applying pressure to the lithium sheet covering the surface of the CSP diaphragm (pressurizing the CSP diaphragm from the side of the lithium sheet) to cause lithiation of the CSP diaphragm. The lithiation process takes less than 45 seconds.

[0083] The ceramic composite lithium-supplementing separator prepared by the above method can be used in lithium-ion batteries. When assembled into a half-cell, the positive electrode housing, positive electrode sheet, ceramic composite lithium-supplementing separator, lithium sheet, nickel foam, and negative electrode housing are pressed into shape, wherein electrolyte is dripped onto the surface of the ceramic composite lithium-supplementing separator. When assembled into a full battery, the positive electrode housing, positive electrode sheet, ceramic composite lithium-supplementing separator, negative electrode sheet, stainless steel sheet, nickel foam, and negative electrode housing are pressed into shape, wherein electrolyte is dripped onto the surface of the ceramic composite lithium-supplementing separator. The above-mentioned half-cell is preferably a lithium iron phosphate|Li half-cell or a graphite half-cell; the above-mentioned full battery is preferably a lithium iron phosphate|graphite full battery.

[0084] Example 1

[0085] CoS 2 / Preparation of Co3S4 composite materials

[0086] Dissolve 8g of anhydrous cobalt acetate in 350mL of ethylene glycol, then add 10.8g of polyvinyl pyrrolidone (PVP, molecular weight 58000) and 8g of thiourea, and stir thoroughly to dissolve it completely. Transfer the solution to a round-bottom flask and place it in an oil bath, condense and reflux at 150°C for 4h, and after cooling, filter and wash three times with deionized water and dry in an 80°C oven for 12h to obtain the precursor. Transfer the precursor to a tube furnace and keep it at 800°C for 2h. The atmosphere in the furnace is argon and the heating rate is 2°C·min -1 The resulting black powder was ground and mixed evenly with sulfur powder in a mass ratio of 3:1. The mixture was then poured into a corundum boat and tightly wrapped with tin foil. The mixture was then sulfurized at 300°C for 2 hours in an argon atmosphere tube furnace. The tin foil was removed and the mixture was treated at 300°C for another 2 hours to volatilize the excess sulfur, yielding the product CoS2 / Co3S4.

[0087] Preparation of CSP diaphragms

[0088] The CoS2 / Co3S4 composite, Super P, and PVDF were dispersed in NMP at a mass ratio of 7:2:1 and ground to a fine, uniform slurry. This slurry was then coated onto a commercial PP separator using a doctor blade and then dried in a 50°C vacuum oven to produce a CSP separator. By adjusting the doctor blade thickness, coated separators with varying loadings could be obtained.

[0089] Preparation of LCSP membrane

[0090] The CSP diaphragm was cut into 19mm diameter discs. An appropriate amount of electrolyte was added, and then a lithium sheet was placed on top, applying a certain amount of pressure. After a certain reaction time, the lithium sheet was removed to obtain the LCSP lithium-supplemented diaphragm. The reaction was carried out under an inert atmosphere in a glove box.

[0091] Comparative Example 1

[0092] Preparation of CoS2 / Co3S4 composite materials

[0093] Dissolve 8g of anhydrous cobalt acetate in 350mL of ethylene glycol, then add 10.8g of polyvinyl pyrrolidone (PVP, molecular weight 58000) and 8g of thiourea, and stir thoroughly to dissolve it completely. Transfer the solution to a round-bottom flask and place it in an oil bath, condense and reflux at 150°C for 4h, and after cooling, filter and wash three times with deionized water and dry in an 80°C oven for 12h to obtain the precursor. Transfer the precursor to a tube furnace and keep it at 800°C for 2h. The atmosphere in the furnace is argon and the heating rate is 2°C·min -1 The resulting black powder was ground and mixed evenly with sulfur powder in a mass ratio of 3:1. The mixture was then poured into a corundum boat and tightly wrapped with tin foil. The mixture was then sulfurized at 300°C for 2 hours in an argon atmosphere tube furnace. The tin foil was removed and the mixture was treated at 300°C for another 2 hours to volatilize the excess sulfur, yielding the product CoS2 / Co3S4.

[0094] Preparation of CSP diaphragms

[0095] CoS2 / Co3S4 composite, Super P and PVDF were dispersed in NMP solvent at a mass ratio of 7:2:1.

[0096] The slurry was ground into a fine and uniform slurry, which was then coated onto a commercial PP separator with a doctor blade and then dried in a vacuum oven at 50°C to obtain a CSP separator. The CSP separator was cut into discs with a diameter of 19 mm.

[0097] Comparative Example 2

[0098] Preparation of PP diaphragm

[0099] The commercial PP diaphragm was placed in a vacuum oven at 50°C and baked, and then cut into discs with a diameter of 19 mm after baking.

[0100] Preparation of electrode

[0101] Lithium iron phosphate electrode: Lithium iron phosphate, Super P, and PVDF are added to a vacuum mixer at a mass ratio of 94:2:4. An appropriate amount of NMP solvent is added and stirred to form a fine, uniform slurry. This slurry is then applied to carbon-coated aluminum foil using a spatula and dried in a 70°C oven overnight. The electrode is then compacted using a roller press and cut to the desired size for later use.

[0102] The preparation method of graphite pole pieces is basically the same as that of lithium iron phosphate pole pieces. It only requires replacing the binder with PAALi and the current collector with copper foil.

[0103] The lithium iron phosphate electrode loading is 12-15 mg cm -2 , the graphite electrode loading is 6-8 mg cm -2 .

[0104] Battery assembly and testing

[0105] Battery assembly

[0106] The battery was assembled in a glove box with an argon atmosphere, and the water and oxygen contents did not exceed 0.1 ppm.

[0107] The button cell model of this solution is CR2032. For the half-cell, the positive electrode plate and the diaphragm prepared in the above embodiment 1, comparative example 1 or comparative example 2 are stacked on the positive electrode shell in sequence, and the electrolyte is added and then the lithium sheet and nickel foam are stacked. After the negative electrode shell is covered, it is transferred to the packaging machine for compression molding. When assembling a full lithium-ion battery, the lithium sheet is replaced with the negative electrode plate, and a stainless steel sheet is added between it and the nickel foam. In the above, the positive electrode plate is a lithium iron phosphate plate, and the negative electrode plate is a graphite plate.

[0108] The electrolyte used in the tested batteries was a 1M lithium hexafluorophosphate (LiPF6) solution in ethylene carbonate (EC) / diethyl carbonate (DEC) (volume ratio 1:1), with 5wt% fluoroethylene carbonate (FEC) added as an additive. The electrolyte volume was 50μL (button cell).

[0109] When assembling a full battery, the negative electrode capacity is 10% excess to match the positive electrode capacity.

[0110] The test voltage range for graphite half-cell is 0.01-2 V, and the test voltage range for lithium iron phosphate|Li half-cell and lithium iron phosphate|graphite full-cell is 2.5-4 V. The CV curve test voltage range is 2.5-4 V, and the scan rate is 0.1 mV·s -1 All battery tests were performed at 25°C.

[0111] Figure 1 (a) is the XRD pattern of the synthesized CoS2 / Co3S4 composite material. The peaks of the sample completely correspond to the standard cards of CoS2 (PDF#70-2866) and Co3S4 (PDF#42-1448), proving the successful preparation of the composite material and the absence of other impurities. The wide peak width of the diffraction peak in the figure indicates that the material particle size is small, which is conducive to the rapid progress of the subsequent lithiation reaction. Figure 1 As shown in (b), the product after in situ lithiation treatment has two smaller diffraction peaks at 27.0° and 44.9°, confirming the formation of Li2S after the reaction. No diffraction peak of single Co was observed, possibly because the Co particles are too small and the diffraction peak is obscured by the background (the peak at around 18° is the diffraction peak of the polyimide tape used in sample preparation).

[0112] The CSP diaphragm was characterized by SEM, such as Figure 2As shown in (a, b), the CoS2 / Co3S4 composite material is nanoscale particles of uniform size with a diameter of about 50 nm and is evenly distributed on the diaphragm substrate. Figure 2 (c, d) SEM images of the LCSP separator coating surface show little change in the overall morphology after lithiation. The particle distribution remains flat and uniform, with only a slight increase in size and closer adhesion between particles. The nano-sized particle structure facilitates a rapid lithiation reaction and a higher degree of lithiation. Furthermore, lithium ions can be rapidly released during charging, providing more lithium replenishment capacity.

[0113] from Figure 3 As can be seen, the capacity of the LCSP separator is much higher than that of the CSP separator and the commercial PP separator, indicating that the LCSP separator has been in situ lithiated through brief contact with the metallic lithium segment, replenishing a large amount of lithium. At the same time, the capacity of the CSP separator and the commercial PP separator is almost the same, which shows that the CoS2 / Co3S4 composite material has good cycling stability and does not consume additional lithium ions.

[0114] from Figure 4 (ac) The cross-sectional SEM images and corresponding X-ray energy dispersive spectrum (EDS) analysis of the CSP diaphragm show that the coating thickness of the CSP diaphragm is only 2.4 μm, and the CoS2 / Co3S4 composite material is evenly distributed in it. In the LCSP diaphragm after in-situ lithiation reaction ( Figure 4 (d)), due to the introduction of lithium ions, the material particle size becomes larger and the coating thickness increases accordingly, but it is still only 3μm, which does not have a significant impact on the volume energy density at the battery scale. Figure 4 The EDS spectra of (e, f) show that the lithiated product Li2S / Co remains uniformly distributed in the coating.

[0115] A lithium iron phosphate|graphite full battery system was used to study the electrochemical properties of the LCSP lithium-supplementing separator. Figure 5 Graphite and lithium iron phosphate half-cells at 0.5C (graphite: 1C = 372mA g -1 , lithium iron phosphate: 1C = 170mA g -1 ) and the charge-discharge curves of different cycles. The voltage of the lithium iron phosphate positive electrode rises rapidly to 3.45V during charging and remains stable, corresponding to the phase transition from iron phosphate to lithium iron phosphate. The voltage rises again until the lithium ions are completely released and the charge is cut off at the upper limit voltage. Its first cycle specific capacity is 153mA·h·g -1 After 250 cycles, there is still 151mA·h·g -1 The capacity decay is basically 0, and the positive electrode charge and discharge curve remains almost unchanged. The first cycle discharge capacity of the graphite negative electrode is 424mA·h·g -1However, the charge capacity is only 372mA·h·g -1 The first-cycle Coulombic efficiency was 88%. Capacity loss was primarily due to irreversible capacity caused by the formation of the SEI film on the surface during the initial discharge. The graphite anode maintained a capacity of 83% after 200 cycles, and the charge-discharge curve remained stable, with only a slight decrease in capacity. Both the positive and negative electrodes exhibited excellent cycling and structural stability, thus eliminating the influence of electrode materials and processes on performance in full-cell electrochemical testing.

[0116] Afterwards, a full battery of graphite and lithium iron phosphate was assembled, and the mass of the Li2S / Co coating was matched to 5% of the mass of the positive electrode material. Its first cycle charge and discharge curve is as follows Figure 6 As shown. Each curve in the figure is normalized to a lithium iron phosphate capacity of 1, and the negative and positive electrodes in the full cell are matched at a capacity ratio of 1.1:1. The shaded area marked with the number 1 in the graphite charge-discharge curve represents the capacity loss caused by the formation of the first SEI film. When this is matched with the lithium iron phosphate cathode to assemble a full cell, this irreversible capacity consumes the active lithium ions in the lithium iron phosphate cathode. This corresponds to the difference in discharge specific capacity between the lithium iron phosphate half-cell and the lithium iron phosphate / graphite full cell in the figure, which is the shaded area marked with the number 2.

[0117] The two groups of batteries were tested for constant current charge and discharge. Figure 7 The first cycle charge-discharge curve of the battery at 0.1C current. During charging, the PP separator battery and LCSP separator battery began to delithiation and contribute to capacity at around 2V and 0.5V, respectively, which is consistent with the results of the cyclic voltammetry curve. The first cycle charge specific capacity of the PP separator battery is 163.1mA·h·g -1 , the discharge capacity is 112.6mA·h·g -1 In comparison, the first cycle charge capacity of LCSP diaphragm is as high as 195.5mA·h·g -1 The improvement in charging capacity mainly comes from the capacity contributed by the lithium-supplementing and lithium-deintercalating diaphragm. The discharge capacity of the LCSP diaphragm reaches 150.3mA·h·g -1 , which is basically the same as the maximum capacity that lithium iron phosphate can actually exert, and is 37.7mA·h·g higher than PP diaphragm battery. -1 Thanks to the LCSP separator's replenishment of active lithium ions during the first cycle of charging, the discharge specific capacity of the lithium iron phosphate / graphite full battery has been greatly improved.

[0118] Figure 8(a) Cycling performance of a lithium iron phosphate / graphite full battery assembled with PP and LCSP separators at 0.5C. A low current of 0.1C was used to activate the battery in the first two cycles and allow the lithium ions in the lithium-replenishing coating to be completely released. The LCSP separator compensates for the active lithium ions in the first cycle, increasing the battery's discharge capacity. Furthermore, the LCSP separator battery still maintained a capacity of 103.5 mA·h·g after 200 cycles. -1 , the capacity retention rate is 74.8%, and the average coulombic efficiency is 99.8%. In comparison, the capacity retention rate of the PP diaphragm battery is only 60%, and the 200-cycle coulombic efficiency is 99.3%. This result further shows that the LCSP diaphragm has good chemical and electrochemical stability during the cycle, and the introduction of the lithium supplement coating does not have a negative impact on the battery performance. On the contrary, the coulombic efficiency and cycle stability of the LCSP diaphragm battery have been improved. Figure 8 As shown in (c), the charge and discharge curves of LCSP separator batteries with different cycles are mostly similar, but the capacity gradually decreases with the increase of cycles. However, the capacity of PP separator batteries not only decreases faster, but also the polarization voltage gradually increases ( Figure 8 (b)). The reason for this may be that the introduction of the inorganic lithium-supplementing coating improves the wettability of the separator to the electrolyte, which accelerates the migration rate of lithium ions at the interface between the electrode and the electrolyte, thereby accelerating the electrode reaction kinetics.

[0119] Figure 9 The first-cycle specific capacity and mass energy density of batteries with different separators were compared. The energy density is calculated based on the total mass of the positive and negative electrodes, while the mass of the lithium-supplementing coating is taken into account in the LCSP separator. During the first cycle of charging of the LCSP separator battery, lithium ions in the Li2S / Co lithium-supplementing coating are released and migrate to the negative electrode. These lithium ions, together with the lithium ions released from the positive electrode, participate in the SEI film formation and the electrode reaction at the negative electrode, compensating for the irreversible capacity loss in the first cycle. As a result, the battery's first-cycle specific discharge capacity is as high as 150.3 mA·h·g -1 , compared with 112.6mA·h·g of PP separator battery -1 Even taking the mass of the lithium-replenishing coating into account, the battery with the LCSP separator still showed 285W·h·kg -1 The high energy density of PP separator battery is only 220W·h·kg -1 , the energy density increased by 29.5%, which was mainly due to the high lithium replenishment capacity of the Li2S / Co composite material.

[0120] In summary, this scheme synthesized CoS2 / Co3S4 composite materials by condensation reflux followed by high-temperature sintering, and coated them on a commercial PP separator. Li2S / Co lithium supplementation separator (LCSP) was prepared by in-situ lithiation. The manufacturing process of this functional separator is compatible with the current lithium-ion battery production process and is an ideal industrial lithium supplementation method. The LCSP separator only takes 45 seconds to fully lithiate, and the Li2S / Co coating generated after lithiation has a high lithium supplementation capacity (993mA·h·g -1 ) By adjusting the loading of the lithium-replenishing coating, the degree of lithium replenishment can be precisely controlled. LCSP separators significantly increase the specific capacity of lithium iron phosphate / graphite batteries, and the energy density is also increased accordingly.

[0121] The above description of the embodiments is intended to facilitate understanding and use of the invention by those skilled in the art. It will be apparent that those skilled in the art can readily make various modifications to these embodiments and apply the general principles described herein to other embodiments without requiring inventive effort. Therefore, the present invention is not limited to the above-described embodiments. Improvements and modifications made by those skilled in the art based on the disclosure of the present invention, without departing from the scope of the present invention, should be within the scope of protection of the present invention.

Claims

1. A method for preparing a ceramic composite lithium supplementing diaphragm, characterized in that: The steps include: S1: Preparation of CoS2 / Co3S4 composite materials: A cobalt source is dissolved in ethylene glycol, and then polyvinyl pyrrolidone and a first sulfur source are added to react to obtain a solid precursor; the solid precursor is calcined under a protective atmosphere, and the black powder obtained after calcination is mixed with a second sulfur source, and then transferred to a closed container for calcination to perform sulfurization to obtain a CoS2 / Co3S4 composite material; S2: Preparation of CSP diaphragm: The CoS2 / Co3S4 composite material, conductive carbon black and PVDF are dispersed in an organic solvent and ground to form a slurry, which is then coated on a diaphragm and dried to obtain a CSP diaphragm. S3: Preparation of LCSP membrane: After adding electrolyte to the surface of the CSP diaphragm, a lithium sheet is placed on it. The CSP diaphragm is pressurized by the lithium sheet to perform in-situ lithiation to obtain an LCSP diaphragm.

2. The method for preparing a ceramic composite lithium supplementing diaphragm according to claim 1, characterized in that: Step S1 includes one or more of the following: i) the cobalt source is one or more of anhydrous cobalt acetate, anhydrous cobalt sulfate, anhydrous cobalt nitrate, anhydrous cobalt carbonate, cobalt naphthenate, anhydrous cobalt chloride, anhydrous cobalt bromide, cobalt boroacylate and cobalt citrate; ii) the first sulfur source is thiourea; iii) the mass ratio of the cobalt source, polyvinyl pyrrolidone and the first sulfur source is 6-10:8-12:1-10; iv) the second sulfur source is sulfur powder; v) The mass ratio of the black powder to the second sulfur source is 1 to 6:

1.

3. The method for preparing a ceramic composite lithium supplementing diaphragm according to claim 1, wherein: Step S1 includes one or more of the following: i) ethylene glycol containing a cobalt source, polyvinyl pyrrolidone and thiourea are subjected to condensation reflux reaction at 120-180° C. for 2-6 hours; ii) The solid precursor was heated at 1-5°C·min in an argon atmosphere. -1 The temperature is raised to 800°C at a rate of 100°C and kept at this temperature for 1 to 6 hours; iii) The mixture of the black powder and the sulfur powder is sulfurized at 200-500° C. for 1-6 hours under an argon atmosphere.

4. The method for preparing a ceramic composite lithium supplementing diaphragm according to claim 1, wherein: In step S1, after the sulfurization is completed, the sealed state of the closed container is released, and calcination is continued to completely volatilize the excess sulfur.

5. The method for preparing a ceramic composite lithium supplementing diaphragm according to claim 4, characterized in that: After the vulcanization is completed, the sealed container is unsealed and calcination is continued at 200-500°C for 1-6 hours to completely volatilize the excess sulfur.

6. The method for preparing a ceramic composite lithium supplementing diaphragm according to claim 1, characterized in that: Step S2 includes one or more of the following: i) the conductive carbon black is Super P; ii) the mass ratio of the CoS2 / Co3S4 composite material, the conductive carbon black and the PVDF is 4-8:1-3:1-3; iii) the organic solvent is NMP; iv) The separator is a PP separator.

7. A ceramic composite lithium supplementing diaphragm, characterized in that: The method is prepared by any one of claims 1 to 6.

8. Use of the ceramic composite lithium-supplementing separator according to claim 7 in a lithium-ion battery.

9. The use according to claim 8, characterized in that When the ceramic composite lithium-supplementing diaphragm is assembled in a half-cell, the half-cell is formed by pressing a positive electrode shell, a positive electrode sheet, a ceramic composite lithium-supplementing diaphragm, a lithium sheet, nickel foam and a negative electrode shell, wherein an electrolyte is dripped on the surface of the ceramic composite lithium-supplementing diaphragm; When the ceramic composite lithium-supplementing diaphragm is assembled in a full battery, the full battery is pressed and formed by a positive electrode shell, a positive electrode plate, a ceramic composite lithium-supplementing diaphragm, a negative electrode plate, a stainless steel sheet, nickel foam and a negative electrode shell, wherein an electrolyte is dripped on the surface of the ceramic composite lithium-supplementing diaphragm.

10. The use according to claim 9, characterized in that The half-cell is a lithium iron phosphate|Li half-cell or a graphite half-cell; the full cell is a lithium iron phosphate|graphite full cell.

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