Intermediate layer for negative electrode interface modification of sulfide solid-state lithium battery and preparation method

Abstract

An intermediate layer for negative electrode interface modification of a sulfide solid-state lithium battery and a preparation method. The preparation method comprises the following steps: S1, mixing graphene, a boron-containing compound, and an adhesive solution to form a suspension; and S2, carrying out film-forming treatment on the suspension to obtain a graphene-boron-containing compound intermediate layer. The graphene has a skeletal support structure, so that the electronic conductivity of the intermediate layer can be effectively improved, thereby improving the rate capability of an all-solid-state battery. The boron-containing compound facilitates formation of a lithium-boron alloy during lithium-ion conduction, thereby effectively providing capacity for the negative electrode, avoiding reduction of the energy density of the battery caused by the implantation of the intermediate layer.

Description

Intermediate layer for interface modification of sulfide solid-state lithium battery anode and its preparation method Technical Field

[0001] This invention belongs to the field of solid-state lithium battery technology, and relates to an intermediate layer for modifying the interface of the negative electrode of a sulfide solid-state lithium battery and its preparation method. Background Technology

[0002] Sulfide solid electrolytes have achieved or surpassed the ionic conductivity of liquid electrolytes, making them one of the most promising all-solid-state lithium battery technologies. Lithium metal is considered the holy grail of lithium-ion batteries, and directly using lithium metal as the solid-state battery represents the ultimate path for all-solid-state lithium batteries. However, the solid nature of solid electrolytes still cannot prevent the formation of lithium dendrites during charging and discharging, which can eventually lead to short circuits and battery failure. The negative electrode interface problem in directly using lithium metal as a sulfide all-solid-state lithium battery remains to be solved. Currently, solutions generally include electrolyte modification, alloy negative electrode replacement, and artificially implanted interlayers to suppress lithium dendrite formation. Among these, artificial interlayers are considered the most promising method to solve the lithium dendrite problem at the negative electrode interface. However, for commercially viable all-solid-state lithium batteries, the performance requirements for the artificial interlayer implanted at the negative electrode / electrolyte interface are extremely high. It must meet the requirements for efficient lithium-ion / electron transport while ensuring that its thickness and weight do not reduce the battery's energy density. This necessitates that the interlayer itself possesses high capacity.

[0003] Existing technologies often use nanoscale-thickness graphene artificial interlayers to modify the negative electrode. However, nanoscale graphene interlayers are prone to aggregation. Furthermore, these graphene interlayers are only suitable for modifying the negative electrode of liquid batteries. The negative electrode interface of all-solid-state batteries is different from that of liquid batteries, and it is a rigid contact. For solid-state lithium batteries, existing graphene interlayers cannot fundamentally prevent direct contact between lithium metal and electrolyte.

[0004] Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings and deficiencies of existing technologies and provide an intermediate layer for the modification of the negative electrode interface in sulfide solid-state lithium batteries, as well as its preparation method. This invention utilizes graphene and boron-containing compounds to form a self-supporting artificial intermediate layer, achieving controllable thickness. This improves the ionic / electronic conductivity of the intermediate layer, avoids direct contact between lithium metal and the electrolyte, and suppresses the generation and growth of lithium dendrites. It solves the problems of lithium dendrite formation leading to battery short circuits due to contact between lithium metal and sulfide solid-state electrolytes, and the reduction in lithium-ion / electronic conductivity and energy density caused by negative electrode interface modification in sulfide all-solid-state lithium batteries.

[0006] The objective of this invention can be achieved through the following methods:

[0007] In a first aspect, the present invention provides a method for preparing an intermediate layer for modifying the interface of a sulfide solid-state lithium battery anode, the preparation method comprising the following steps:

[0008] S1. Mix graphene, boron-containing compounds, and adhesive solutions to form a suspension;

[0009] S2. The suspension is subjected to film-forming treatment to obtain a graphene-boron-containing compound intermediate layer.

[0010] As one embodiment of the present invention, in step S1, the boron-containing compound includes at least one of lithium tetrafluoroborate, lithium diacetate borate, boron oxide, lithium borate, and boric acid.

[0011] In one embodiment of the present invention, in step S1, the molar ratio of graphene to boron-containing compound is 30-80:5-40. If the molar ratio is too high, the content of boron-containing compound is low, resulting in a lower capacity of the material; if the molar ratio is too low, the electronic conductivity of the negative electrode decreases, affecting the rate performance of the battery.

[0012] As one embodiment of the present invention, in step S1, the adhesive includes at least one of carboxymethyl cellulose, polytetrafluoroethylene, hydroxypropyl methyl cellulose, ethyl cellulose, polybutadiene block copolymer rubber, and polyvinylidene fluoride.

[0013] As one embodiment of the present invention, in step S1, the solvent used in the adhesive solution includes at least one of toluene, ethanol, isopropanol, xylene, n-heptane, hexyl butyrate, and NMP.

[0014] In one embodiment of the present invention, in step S1, the mixing method includes ultrasonic vibration, wherein the ultrasonic vibration time is 4-8 hours.

[0015] In one embodiment of the present invention, in step S1, the adhesive accounts for 1%-8% of the weight of the adhesive solution; the weight ratio of the adhesive solution to graphene is 1:0.5-2.5.

[0016] As one embodiment of the present invention, in step S2, the film-forming process includes at least one of filtration and coating.

[0017] Furthermore, the filtration process involves obtaining a graphene-boron compound membrane by filtration of the suspension; the coating process involves coating the suspension onto the surface of a PET membrane to obtain a graphene-boron compound membrane.

[0018] In one embodiment of the present invention, in step S2, after film formation treatment, the graphene-boron-containing compound intermediate layer is obtained by drying.

[0019] Furthermore, the drying temperature is 65-150℃.

[0020] In one embodiment of the present invention, in step S2, the thickness of the intermediate layer is 5-30 μm. If the intermediate modification layer is too thin, under certain pressure, the ductility of lithium metal means that the negative electrode cannot completely avoid contact with the electrolyte; if the intermediate modification layer is too thick, it affects the energy density of the battery.

[0021] Secondly, the present invention provides an intermediate layer obtained by the preparation method described above.

[0022] Thirdly, the present invention provides an application of the intermediate layer in the modification of the negative electrode interface of a sulfide solid lithium battery.

[0023] As one embodiment of the present invention, the negative electrode interface modification involves placing an intermediate layer on the surface of the lithium negative electrode.

[0024] As one embodiment of the present invention, the solid-state lithium battery includes a negative electrode current collector, a lithium metal electrode, an intermediate layer, a sulfide electrolyte, a composite positive electrode, and a positive electrode current collector stacked sequentially.

[0025] As one embodiment of the present invention, the composite positive electrode sheet is obtained by mixing a positive electrode material, a sulfide electrolyte, and VGCF; the positive electrode material includes one of NCM111, NCM424, NCM523, NCM622, NCM811, NCM90, NCM95, lithium cobalt oxide, sulfur, and metal sulfides; the metal sulfides include at least one of Fe2S, MoS2, TiS2, and NiS.

[0026] As one embodiment of the present invention, the sulfide electrolyte includes Li7P3S 11 Li 10 GeP2S 12 Li 9.5 4Si 1.74 P 1.44 S 11.7 Cl 0.3 Li6PS5Cl, Li 5.5 PS 4.5 Cl 1.5 Li6PS5Br, Li6PS5I, Li 11 Si2PS 12 Li 10 SnP2S 12 Li 3.25 Ge 0.25 P 0.75 S4, Li 10 Ge(P 1-x Sb x )2S 12 Li6.6 Ge 0.6 P 0.4 At least one of S5I.

[0027] In one embodiment of the present invention, the thickness of the lithium metal electrode sheet is 5-30 μm.

[0028] As one embodiment of the present invention, the mass ratio of the positive electrode material, the sulfide electrolyte, and the VGCF is 50-100:15-30:1-6.

[0029] In some preferred embodiments, the negative current collector includes Cu foil; the positive current collector includes Al foil; and the weight ratio of NCM811, Li5.5PS4.5Cl1.5 electrolyte, and VGCF is 75:22:3.

[0030] Compared with the prior art, the present invention has the following beneficial effects:

[0031] 1. This invention utilizes the ease with which boron-containing compounds form lithium-boron alloys during lithium-ion conduction. Boron has a theoretical capacity as high as 12395 mAh / g, and the volumetric capacity of the formed lithium-boron alloy reaches as high as 3180 mA / cm². 3 This can effectively improve the negative electrode capacity, avoid the reduction of battery energy density by implanting the intermediate layer, and enable the graphene / boron-containing compound intermediate layer itself to provide capacity for lithium-ion transport without reducing battery energy density, and effectively improve the rate performance of the whole battery.

[0032] 2. This invention utilizes the skeletal support structure of graphene, which can effectively improve the electronic conductivity of the intermediate layer, enhance the rate performance of the full battery, avoid direct contact between lithium metal and sulfide electrolyte, and effectively inhibit the formation and growth of lithium dendrites.

[0033] 3. This invention utilizes graphene and boron-containing compounds to form a self-supporting artificial intermediate layer, which can achieve controllable thickness. This improves the ionic / electronic conductivity of the intermediate layer, avoids direct contact between lithium metal and electrolyte, and inhibits the generation and growth of lithium dendrites. It can effectively solve the problem that lithium metal cannot be directly used as the negative electrode in existing sulfide all-solid-state batteries. Attached Figure Description

[0034] Other features, objects, and advantages of the present invention will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings:

[0035] Figure 1 shows the comparison curves of the magnification test between Example 1 and Comparative Example 1;

[0036] Figure 2 is a cross-sectional SEM image of the graphene-boron-containing compound interlayer of Example 3. Detailed Implementation

[0037] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. The following examples are implemented under the premise of the technical solution of the present invention, providing detailed implementation methods and specific operating procedures, which will help those skilled in the art to further understand the present invention. It should be noted that the scope of protection of the present invention is not limited to the following embodiments; any adjustments and improvements made under the concept of the present invention are all within the scope of protection of the present invention.

[0038] Example 1

[0039] 1) Graphene (1g), lithium tetrafluoroborate, and 1g of a 4% polyvinylidene fluoride-NMP mixed solution (60:40 molar ratio) were thoroughly mixed in a 250mL Erlenmeyer flask. After ultrasonic vibration for 5 hours, a gel-like solution was formed. This solution was then coated onto the surface of a PET film to a thickness of 50μm. The film was baked at 80℃ for 24 hours and then peeled off from the PET film surface. The thickness was measured to be 23μm. The composite film was then cut into 10mm diameter circular pieces.

[0040] 2) Preparation of composite cathode: Weigh 75mg NCM811 powder and 22mg Li 5.5 PS 4.5 Cl 1.5 The electrolyte powder and 3 mg of VGCF powder are placed in a mortar and ground for 30 minutes until the powders are evenly mixed.

[0041] 3) Assemble the pressure cell: In a glove box filled with argon gas, weigh 40 mg of Li 5.5 PS 4.5 Cl 1.5 Electrolyte powder was placed in a pressure battery mold with a diameter of 10 mm. A rotating stainless steel column was used to flatten the electrolyte powder, which was then pressed into tablets on a tablet press at a pressure of 120 MPa for 2 minutes. 40 mg of the freshly pressed Li composite cathode powder was weighed out. 5.5 PS 4.5 Cl 1.5 The electrolyte sheet surface is flattened and pressed into a sheet using a tablet press at a pressure of 360 MPa for 2 minutes. A 10 mm diameter Al foil is then placed on the surface of the composite positive electrode sheet as the positive current collector. Li 5.5 PS 4.5 Cl 1.5 Place the cut disc from step 1) on the other side of the electrolyte sheet, then place a 10μm thick lithium strip, and use Cu foil as the negative electrode current collector. After assembly, apply a pressure of 50MPa to obtain a sulfide all-solid-state lithium-ion battery.

[0042] Example 2

[0043] The preparation method of this embodiment is basically the same as that of Example 1, except that: 1) 1g of graphene, lithium tetrafluoroborate and 1g of a mixed solution containing 4% polyvinylidene fluoride-NMP with a molar ratio of 30:40 are thoroughly mixed in a 250mL Erlenmeyer flask and ultrasonically vibrated for 5h to form a gel-like solution. The above solution is coated on the surface of a PET film with a coating thickness of 50μm, baked at 80℃ for 24h, and then peeled off from the surface of the PET film. The thickness is measured to be 23μm. The composite film is then cut into 10mm diameter circular pieces.

[0044] Example 3

[0045] The preparation method of this embodiment is basically the same as that of Example 1, except that: 1) 1g of graphene, lithium tetrafluoroborate and 1g of a mixed solution containing 4% polyvinylidene fluoride-NMP with a molar ratio of 80:40 are thoroughly mixed in a 250mL conical flask and ultrasonically vibrated for 5h to form a gel-like solution. The above solution is coated onto the surface of a PET film with a coating thickness of 50μm, baked at 80℃ for 24h, and then peeled off from the PET film surface. The thickness is measured to be 19.34μm. The composite film is cut into 10mm diameter circular pieces. The cross-sectional SEM image of the graphene-boron compound in the intermediate layer is shown in Figure 2.

[0046] Comparative Example 1

[0047] The difference from Example 1 is that the negative electrode directly uses a 20μm graphite film and a 10μm thick lithium strip, while the other steps are the same, to obtain a sulfide all-solid-state lithium-ion battery.

[0048] Comparative Example 2

[0049] 1) Graphene material with a thickness of 0.35 nm was prepared on the surface of a polyethylene terephthalate (PET) film using chemical vapor deposition (CVD). In an argon-filled glove box, one side of the graphene was in contact with lithium metal, and the material was rolled using the following parameters: temperature 60℃, rolling speed 10 mm / s, and 12 rolls. The PET film was then peeled off to obtain a graphene-modified lithium metal anode with a thickness of 420 μm. This composite film was then cut into 10 mm diameter discs.

[0050] 2) Preparation of composite cathode: Weigh 75mg NCM811 powder and 22mg Li 5.5 PS 4.5 Cl 1.5 The electrolyte powder and 3 mg of VGCF powder are placed in a mortar and ground for 30 minutes until the powders are evenly mixed.

[0051] 3) Assemble the pressure cell: In a glove box filled with argon gas, weigh 40 mg of Li 5.5 PS 4.5 Cl 1.5Electrolyte powder was placed in a pressure battery mold with a diameter of 10 mm. A rotating stainless steel column was used to flatten the electrolyte powder, which was then pressed into tablets on a tablet press at a pressure of 120 MPa for 2 minutes. 40 mg of the freshly pressed Li composite cathode powder was weighed out. 5.5 PS 4.5 Cl 1.5 The electrolyte sheet surface is flattened and pressed into a sheet using a tablet press at a pressure of 360 MPa for 2 minutes. A 10 mm diameter Al foil is then placed on the surface of the composite positive electrode sheet as the positive current collector. Li 5.5 PS 4.5 Cl 1.5 Place the cut disc from step 1) on the other side of the electrolyte sheet, then place a 10μm thick lithium strip, and use Cu foil as the negative electrode current collector. After assembly, apply a pressure of 50MPa to obtain a sulfide all-solid-state lithium-ion battery.

[0052] Performance testing

[0053] The Xinwei Battery Testing System (model: CT-4000) was used to test the sulfide-based all-solid-state lithium-ion battery. The rate performance of the all-solid-state battery was tested using a charge-discharge cycle of 0.5C (5 cycles) - 1C (5 cycles) - 2C (5 cycles) - 3C (5 cycles). The discharge capacity of the sulfide-based all-solid-state lithium-ion battery was tested using a 0.1C rate charge-discharge cycle. The mass energy density of the all-solid-state battery was calculated using formula (1).

[0054] Mass energy density (Wh / kg) = Battery discharge capacity (mAh) * 3.6 (V) / kg (1)

[0055] Figure 1 shows the rate test comparison curves of Example 1 and the Comparative Example. Example 1, under rate tests of 0.5C-1C-1.5C-2C-3C, exhibited discharge specific capacities of 176mAh / g-159mAh / g-147mAh / g-134mAh / g-107mAh / g, respectively; Comparative Example 1, under the same rate tests, exhibited discharge specific capacities of 169mAh / g-150mAh / g-131mAh / g-113mAh / g-79mAh / g, respectively.

[0056] Through testing, the discharge capacities of Example 2 and Comparative Example 2 at a 0.1C rate were 210 mAh / g and 100 mAh / g, respectively, which translates to discharge capacities of 6.3 mAh and 3 mAh. The weight of the full battery was 85 mg for both. Therefore, the energy density of Example 2 was 266.8 Wh / kg, and the energy density of Comparative Example 2 was 127 Wh / kg.

[0057] The specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the specific embodiments described above, and those skilled in the art can make various modifications or variations within the scope of the claims, which do not affect the essence of the present invention.

Claims

1. A method for preparing an intermediate layer for modifying the interface of a sulfide solid-state lithium battery anode, characterized in that, The preparation method includes the following steps: S1. Mix graphene, boron-containing compounds, and adhesive solutions to form a suspension; S2. The suspension is subjected to film-forming treatment to obtain a graphene-boron-containing compound intermediate layer.

2. The preparation method according to claim 1, characterized in that, In step S1, the boron-containing compound includes at least one of lithium tetrafluoroborate, lithium diacetate borate, boron oxide, lithium borate, and boric acid.

3. The preparation method according to claim 1, characterized in that, In step S1, the molar ratio of graphene to boron-containing compound is 30-80:5-40.

4. The preparation method according to claim 1, characterized in that, In step S1, the adhesive includes at least one of carboxymethyl cellulose, polytetrafluoroethylene, hydroxypropyl methyl cellulose, ethyl cellulose, polybutadiene block copolymer rubber, and polyvinylidene fluoride.

5. The preparation method according to claim 1, characterized in that, In step S1, the solvent used in the adhesive solution includes at least one of toluene, ethanol, isopropanol, xylene, n-heptane, hexyl butyrate, and NMP; the adhesive accounts for 1%-8% of the weight of the adhesive solution; and the weight ratio of the adhesive solution to graphene is 1:0.5-2.

5.

6. The preparation method according to claim 1, characterized in that, In step S2, the film-forming process includes at least one of filtration and coating.

7. The preparation method according to claim 1, characterized in that, In step S2, the thickness of the intermediate layer is 5-30 μm.

8. An intermediate layer obtained by the preparation method according to any one of claims 1-7.

9. The application of an intermediate layer obtained by any one of the preparation methods described in claims 1-8 in the modification of the interface of a sulfide solid lithium battery anode.

10. The application according to claim 9, characterized in that, The negative electrode interface modification involves placing an intermediate layer on the surface of the lithium negative electrode.

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