Semi-solid lithium-sulfur battery composite pole piece and preparation process thereof

Abstract

The invention discloses a semi-solid lithium-sulfur battery composite pole piece and a preparation process, and relates to the technical field of energy storage materials. The pole piece adopts a gradient composite structure of a sulfur-based active layer, a conductive network layer, a transition layer and an electrolyte interface layer, wherein the sulfur-based active layer is combined with a surface modifier through a microporous carbon carrier to realize efficient fixation of sulfur; the conductive network layer constructs a three-dimensional interpenetrating conduction channel, and the electron / ion transmission efficiency is synchronously improved; the transition layer buffers volume expansion stress through gradient composite design; and the electrolyte interface layer forms a low-impedance compact structure through in-situ polymerization. The preparation process comprises the key procedures of current collector surface treatment, conductive layer construction, gradient hot-pressing compounding, interface layer in-situ forming and the like. According to the technical scheme, the problems of capacity fading, interface failure and the like of a traditional lithium-sulfur battery are effectively solved, and the lithium-sulfur battery is suitable for development of high-energy-density energy storage devices.

Description

Technical Field

[0001] The present invention relates to the technical field of energy storage materials, and in particular to a semi-solid lithium-sulfur battery composite pole piece and a preparation process thereof. Background Art

[0002] Lithium-sulfur batteries have the advantages of high theoretical energy density, abundant and readily available raw materials, and low prices. They can be widely used in aerospace, new energy vehicles and other fields, and are one of the main development directions of the next generation of high-energy-density batteries.

[0003] At present, China's patent application number: CN202011562615.5 discloses a semi-solid lithium-sulfur battery composite electrode sheet, a semi-solid lithium-sulfur battery and its preparation method. The composite electrode sheet includes a positive electrode sheet or a negative electrode sheet, and a composite solid electrolyte arranged on the outside of the positive electrode sheet or the negative electrode sheet. The bare cell of the semi-solid lithium-sulfur battery includes a diaphragm, at least one positive electrode sheet and at least one negative electrode sheet. The diaphragm has a continuous bending structure, and the positive electrode sheet and the negative electrode sheet are sequentially arranged in the groove formed by the continuous bending of the diaphragm.

[0004] However, the dissolution and migration of polysulfides in the electrolyte of lithium-sulfur batteries leads to irreversible loss of active materials, causing capacity decay; the drastic volume change of sulfur during charging and discharging causes damage to the electrode structure; the poor solid-solid interface contact leads to obstructed charge transfer, affecting the battery rate performance; although the existing technology has improved some problems through multi-layer structure design, there are still problems such as insufficient interlayer bonding strength and complex preparation process, making it difficult to achieve both high energy density and long cycle life. Summary of the Invention

[0005] The object of the present invention is to provide a semi-solid lithium-sulfur battery composite electrode and a preparation process to solve the problems raised in the above background technology.

[0006] In order to achieve the above-mentioned objectives, the present invention adopts the following technical scheme: a semi-solid lithium-sulfur battery composite electrode, comprising a three-dimensional gradient composite structure consisting of an inner layer, an intermediate layer and an outer layer, wherein the inner layer is a sulfur-based active material layer, which adopts a composite of microporous carbon-loaded sulfur particles and a surface modifier; the intermediate layer is a conductive network reinforcement layer, which is a three-dimensional interpenetrating network formed by carbon-based nanomaterials and polar polymers; the outer layer is a semi-solid electrolyte interface layer, which comprises an in-situ polymerized ion conductive polymer matrix and an inorganic nano reinforcement phase; a transition layer is provided between the conductive network reinforcement layer and the semi-solid electrolyte interface layer, wherein the transition layer comprises a composite of lithiated polymer microspheres and conductive carbon black, and the particle size of the microspheres is gradiently distributed to buffer the volume expansion stress.

[0007] Preferably, the microporous carbon support of the sulfur-based active material layer has a hierarchical pore structure, comprising three levels of interconnected channels of micropores, mesopores and macropores, and the surface of the sulfur-carrying particles is coated with a nitrogen-containing polymer modification layer by chemical bonding to improve the sulfur fixation ability.

[0008] Preferably, the conductive network reinforcement layer is formed by interweaving graphene nanosheets and carbon nanotubes to form a three-dimensional conductive skeleton, the pores of which are filled with polar polymers to form continuous ion transmission channels, and the polar polymers include polyvinylidene fluoride-based copolymers.

[0009] Preferably, the semi-solid electrolyte interface layer forms a continuous and dense structure through ultraviolet curing technology, and comprises a composite phase of a cross-linked polyether polymer matrix and ceramic nanofibers, wherein the ceramic nanofibers are directionally arranged along the thickness direction of the interface layer.

[0010] Preferably, the thickness ratio of each functional layer in the three-dimensional gradient composite structure is sulfur-based active material layer: conductive network reinforcement layer: electrolyte interface layer = (3-5): (1-2): 1, and the interface between each layer is a corrugated staggered structure to increase the bonding area.

[0011] In addition, the present invention also provides a process for preparing a semi-solid lithium-sulfur battery composite electrode, comprising the following steps: S1. Pre-treating the metal current collector by plasma etching in an inert atmosphere to form a micro-nanostructured surface and depositing a lithium titanate transition layer to enhance interface bonding strength. S2, constructing a conductive network reinforcement layer on the surface of the metal current collector by electrospinning technology; S3, compounding the sulfur-based active material layer and the conductive network reinforcement layer using a multi-stage hot pressing process; S4. Forming a semi-solid electrolyte interface layer on the surface of the composite layer through in-situ UV polymerization technology.

[0012] Preferably, the construction of the conductive network reinforcement layer includes the steps of carbon-based nanomaterial deposition, polar polymer precursor solution impregnation and heat treatment, wherein the heat treatment temperature gradient is controlled to be raised in stages from 80°C to 180°C.

[0013] Preferably, the multi-stage hot pressing process includes a preheating stage, a pressurized infiltration stage and a shaping stage, and the active material and the conductive layer form a mechanical interlocking structure by controlling the pressure gradient, and the pressure range is 0.5 MPa to 5 MPa.

[0014] Preferably, the process of the in-situ UV polymerization technology comprises uniformly coating the electrolyte precursor solution on the surface of the composite layer, initiating a cross-linking reaction of the polymer matrix by UV irradiation, and performing a post-curing treatment to form an interfacial chemical bond.

[0015] Preferably, after the semi-solid electrolyte interface layer is formed, a surface modification process is performed, including plasma activation treatment and chemical vapor deposition to deposit a nano-scale protective film layer to improve interface stability.

[0016] Compared with the prior art, the present invention has the following beneficial effects: The present invention achieves efficient sulfur loading and polysulfide anchoring through the synergistic effect of the hierarchical pore carbon carrier and the surface chemical modification layer, and simultaneously improves the electron transmission efficiency and ion migration ability through the three-dimensional interpenetrating conductive network; The gradient transition layer of the present invention effectively buffers volume expansion stress through elastic deformation, and inhibits dendrite growth through the directionally enhanced electrolyte interface layer, thereby improving structural stability; The present invention adopts an in-situ polymerization process to form a dense and continuous solid-solid interface, significantly reducing the interfacial charge transfer resistance, and further enhancing the interfacial chemical stability through a surface modification process; The process steps of the present invention are compatible with continuous production equipment, greatly reducing production costs. The pretreatment technology is used to enhance interlayer bonding and improve product yield. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 This is a schematic structural diagram of a composite electrode for a semi-solid lithium-sulfur battery according to the present invention; Figure 2 The figure is a flowchart of the process for preparing the composite pole piece of the semi-solid lithium-sulfur battery of the present invention.

[0018] In the figure: sulfur-based active material layer-1, conductive network reinforcement layer-2, semi-solid electrolyte interface layer-3, transition layer-4. DETAILED DESCRIPTION

[0019] In order to further explain the technical solution of the present invention, specific embodiments are described in detail below.

[0020] See also Figure 1The present invention provides a semi-solid lithium-sulfur battery composite electrode, including a three-dimensional gradient composite structure consisting of an inner layer, an intermediate layer and an outer layer. The inner layer is a sulfur-based active material layer 1, which adopts a composite of microporous carbon-supported sulfur particles and a surface modifier. The microporous carbon carrier increases the sulfur loading capacity, and the surface modifier inhibits the dissolution of polysulfides; the intermediate layer is a conductive network reinforcement layer 2, which is a three-dimensional interpenetrating network formed by carbon-based nanomaterials and polar polymers. The three-dimensional network improves the electron conduction efficiency and increases the ion conductivity by 10%. The outer layer is a semi-solid electrolyte interface layer 3, which includes an in-situ polymerized ion conductive polymer matrix and an inorganic nano-reinforcement phase to reduce the impedance of the continuous interface layer; a transition layer 4 is provided between the conductive network reinforcement layer 2 and the semi-solid electrolyte interface layer 3, and the transition layer 4 includes a composite of lithiated polymer microspheres and conductive carbon black. The particle size of the microspheres is gradiently distributed to buffer the volume expansion stress, reduce the volume expansion rate, and improve the cycle life.

[0021] Among them, the microporous carbon carrier of the sulfur-based active material layer 1 has a hierarchical pore structure, which includes three-level interconnected channels of micropores, mesopores and macropores. The hierarchical pores improve the sulfur utilization rate and ion diffusion rate. The surface of the sulfur-carrying particles is coated with a nitrogen-containing polymer modification layer by chemical bonding to improve the sulfur fixation ability. The polysulfide anchoring improves the efficiency and the shuttle effect inhibition rate. The conductive network enhancement layer 2 is formed by interweaving graphene nanosheets and carbon nanotubes to form a three-dimensional conductive skeleton. The polar polymer is filled in the pores to form a continuous ion transmission channel. The polar polymer includes a polyvinylidene fluoride copolymer to enhance the polar group. Lithium ion migration number, the semi-solid electrolyte interface layer 3 forms a continuous and dense structure through ultraviolet curing technology, which includes a composite phase of a cross-linked polyether polymer matrix and ceramic nanofibers, wherein the ceramic nanofibers are directionally arranged along the thickness direction of the interface layer to improve the puncture resistance and dendrite suppression efficiency. The thickness ratio of each functional layer in the three-dimensional gradient composite structure is sulfur-based active material layer 1: conductive network reinforcement layer 2: electrolyte interface layer 3 = (3-5): (1-2): 1, and the interfaces between the layers are corrugated staggered structures to increase the bonding area, improve the interlayer peeling force, and ensure the interface bonding effect.

[0022] See also Figure 1 and Figure 2 The present invention provides a process for preparing a semi-solid lithium-sulfur battery composite electrode, comprising the following steps: S1. Pre-treating the metal current collector by plasma etching in an inert atmosphere to form a micro-nanostructured surface and depositing a lithium titanate transition layer to enhance interface bonding strength. S2, constructing a conductive network reinforcement layer 2 on the surface of the metal current collector by electrospinning technology; S3, compounding the sulfur-based active material layer 1 and the conductive network reinforcement layer 2 using a multi-stage hot pressing process; S4. Forming a semi-solid electrolyte interface layer 3 on the surface of the composite layer by in-situ UV polymerization technology.

[0023] Among them, the construction of the conductive network reinforcement layer 2 includes carbon-based nanomaterial deposition, polar polymer precursor solution impregnation and heat treatment processes, wherein the heat treatment temperature gradient is controlled to be 80°C to 180°C in stages to avoid thermal decomposition of the polymer and improve crystallinity. The multi-stage hot pressing process includes a preheating stage, a pressurized infiltration stage and a shaping stage. The active material and the conductive layer form a mechanical interlocking structure through pressure gradient control, and the pressure range is 0.5MPa to 5MPa, which improves the interlayer shear strength and ensures the stability of the structure. The process of in-situ UV polymerization technology includes uniformly coating the electrolyte precursor solution on the surface of the composite layer to reduce the coating thickness deviation and material waste rate, inducing the cross-linking reaction of the polymer matrix by ultraviolet irradiation, and implementing post-curing treatment to form interfacial chemical bonding, thereby improving the interfacial chemical bond density. After the semi-solid electrolyte interface layer 3 is formed, a surface modification process is implemented, including plasma activation treatment and chemical vapor deposition to deposit a nano-scale protective film layer to improve interface stability, reduce the electrolyte decomposition rate, and improve high-temperature performance retention.

[0024] Example 1 This embodiment provides a method for preparing a semi-solid lithium-sulfur battery composite electrode. First, a microporous carbon support with a three-level pore structure is used: micropores of 0.5 nm, mesopores of 5 nm, and macropores of 100 μm. The sulfur content reaches 5.2 mg / cm by melt impregnation. 2 The polypyrrole surface was then modified under nitrogen to form a nitrogen-containing polymer coating approximately 50 nm thick. The conductive network reinforcement layer was prepared using an electrospinning process. Graphene nanosheets and carbon nanotubes (CNTs) were dispersed in a DMF solution at a mass ratio of 3:1. This was then deposited onto the surface of an aluminum foil current collector to form a three-dimensional framework with a porosity of 75%. This framework was then impregnated with a PVDF-HFP copolymer solution containing 10 wt% lithium bis(trifluoromethanesulfonyl)imide. After gradient heat treatment at 80°C-180°C, a composite layer with both electron and ion conductivity was obtained. For the transition layer, lithiated PMMA microspheres with a particle size gradient of 20 / 40 / 60 μm were mixed with acetylene black in a 1:1 mass ratio. A 15 μm thick buffer layer was formed using a doctor blade coating method. The semi-solid electrolyte interface layer is formed by coating a polyethylene glycol diacrylate precursor solution containing 15wt% alumina nanofibers (diameter 200nm, aspect ratio >50), curing it under a UV light intensity of 300mJ / cm², and finally curing it in a vacuum at 60℃ for 2 hours to complete the electrode preparation.

[0025] According to SEM morphology analysis and testing, the electrode has an initial specific capacity of 1350mAh / g at a rate of 0.2C, a capacity retention rate of 92% after 100 cycles, an interface impedance of 48Ω·cm², and a volume expansion rate of 13.5%.

[0026] Example 2 This example optimizes the design based on Example 1 and increases the sulfur loading to 6.5 mg / cm 2 , and adjust the thickness ratio of each functional layer to 5:2:1. In the specific implementation, a graded carbon carrier with larger pore size is used: micropore 1nm / mesopore 10nm / macroporous 150μm, and the peak pressure is increased to 6MPa during the hot pressing composite stage to enhance the filling density of the active material. 5wt% titanium carbide nanowires are introduced into the conductive network layer as a reinforcing phase to increase the conductivity of the three-dimensional skeleton to 3500S / m. The interface layer uses directional arranged boron nitride nanosheets instead of alumina fibers, and after UV curing, a uniform and dense structure with a thickness of 20±1μm is formed.

[0027] Testing of the prepared electrode showed that the battery energy density reached 585Wh / kg, and the capacity retention rate was 85% after 200 cycles. The puncture resistance of the interface layer measured by a nanoindenter was increased to 55MPa, and the cycle performance retention rate exceeded 90% in a high temperature environment of 60°C.

[0028] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, it is still possible for those skilled in the art to modify the technical solutions described in the aforementioned embodiments or to substitute equivalents for some of the technical features. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

Claims

1. A semi-solid lithium-sulfur battery composite electrode, characterized by: The invention comprises a three-dimensional gradient composite structure consisting of an inner layer, an intermediate layer and an outer layer, wherein the inner layer is a sulfur-based active material layer (1), which is a composite of microporous carbon-supported sulfur particles and a surface modifier; the intermediate layer is a conductive network reinforcement layer (2), which is a three-dimensional interpenetrating network formed by carbon-based nanomaterials and polar polymers; the outer layer is a semi-solid electrolyte interface layer (3), which comprises an in-situ polymerized ion conductive polymer matrix and an inorganic nano reinforcement phase; a transition layer (4) is provided between the conductive network reinforcement layer (2) and the semi-solid electrolyte interface layer (3), and the transition layer (4) comprises a composite of lithiated polymer microspheres and conductive carbon black, wherein the microsphere particle size is distributed in a gradient to buffer the volume expansion stress.

2. A semi-solid lithium-sulfur battery composite electrode according to claim 1, characterized in that: The microporous carbon carrier of the sulfur-based active material layer (1) has a hierarchical pore structure, comprising three levels of interconnected channels of micropores, mesopores and macropores, and the surface of the sulfur-carrying particles is coated with a nitrogen-containing polymer modification layer by chemical bonding to improve the sulfur fixation ability.

3. The semi-solid lithium-sulfur battery composite electrode according to claim 1, characterized in that: The conductive network reinforcement layer (2) is formed by interweaving graphene nanosheets and carbon nanotubes to form a three-dimensional conductive skeleton, and the pores of the conductive network reinforcement layer are filled with polar polymers to form continuous ion transmission channels, and the polar polymers include polyvinylidene fluoride-based copolymers.

4. The semi-solid lithium-sulfur battery composite electrode according to claim 1, characterized in that: The semi-solid electrolyte interface layer (3) forms a continuous dense structure through ultraviolet curing technology, and comprises a composite phase of a cross-linked polyether polymer matrix and ceramic nanofibers, wherein the ceramic nanofibers are directionally arranged along the thickness direction of the interface layer.

5. The semi-solid lithium-sulfur battery composite electrode according to claim 1, characterized in that: The thickness ratio of each functional layer in the three-dimensional gradient composite structure is sulfur-based active material layer (1): conductive network reinforcement layer (2): electrolyte interface layer (3) = (3-5): (1-2): 1, and the interface between each layer is a corrugated staggered structure to increase the bonding area.

6. A process for preparing a semi-solid lithium-sulfur battery composite pole piece, according to any one of claims 1 to 5, characterized in that: The following steps are involved: S1. Pre-treating the metal current collector by plasma etching in an inert atmosphere to form a micro-nanostructured surface and depositing a lithium titanate transition layer to enhance interface bonding strength. S2, constructing a conductive network reinforcement layer (2) on the surface of the metal current collector by electrospinning technology; S3, using a multi-stage hot pressing process to composite the sulfur-based active material layer (1) and the conductive network reinforcement layer (2); S4. Forming a semi-solid electrolyte interface layer (3) on the surface of the composite layer by in-situ UV polymerization technology.

7. The process for preparing a semi-solid lithium-sulfur battery composite electrode according to claim 6, characterized in that: The construction of the conductive network reinforcement layer (2) includes the steps of carbon-based nanomaterial deposition, polar polymer precursor solution impregnation and heat treatment, wherein the heat treatment temperature gradient is controlled to be raised in stages from 80°C to 180°C.

8. The process for preparing a semi-solid lithium-sulfur battery composite electrode according to claim 6, characterized in that: The multi-stage hot pressing process includes a preheating stage, a pressurized infiltration stage, and a shaping stage. The active material and the conductive layer form a mechanical interlocking structure by controlling the pressure gradient, and the pressure range is 0.5 MPa to 5 MPa.

9. The process for preparing a semi-solid lithium-sulfur battery composite electrode according to claim 6, characterized in that: The in-situ UV polymerization process includes uniformly coating the electrolyte precursor solution on the surface of the composite layer, initiating a cross-linking reaction of the polymer matrix through UV irradiation, and performing a post-curing treatment to form an interfacial chemical bond.

10. The process for preparing a semi-solid lithium-sulfur battery composite electrode according to claim 6, characterized in that: After the semi-solid electrolyte interface layer (3) is formed, a surface modification process is performed, including plasma activation treatment and chemical vapor deposition to deposit a nano-scale protective film layer to improve interface stability.

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