Bipolar electrode containing three-dimensional distribution lithium fluoride and preparation method thereof

Abstract

The invention relates to a bipolar electrode containing three-dimensional distribution lithium fluoride and a preparation method and application thereof, the electrode comprises a positive electrode active material layer, a current collector and a lithium carbon material layer, and the current collector is arranged between the positive electrode active material layer and the lithium carbon material layer; active substances in the lithium-carbon material layer comprise lithium-containing particles, carbon nanotubes on the surfaces of the lithium-containing particles are interwoven to form a three-dimensional porous skeleton, and at least one of the surfaces of the lithium-containing particles, the surfaces of the three-dimensional porous skeleton or pores contains a carbon fluoride material; lithium fluoride is generated in situ between the carbon fluoride material present on the surface of the lithium-containing particles and the lithium-containing particles. The lithium fluoride contributes to uniform deposition of lithium and inhibits growth of lithium dendrites; the carbon nanotubes construct a three-dimensional network channel porous framework, lithium ions and electrons can be regulated and controlled at the same time, uniform deposition of lithium is facilitated, space is provided for volume expansion of lithium-containing particles, and the electrode has excellent cycle performance.

Description

Technical Field

[0001] The present application relates to the field of lithium battery technology, and in particular to a bipolar electrode containing three-dimensionally distributed lithium fluoride and a preparation method thereof. Background Art

[0002] In recent years, with the development of new energy vehicles, the energy density of commercial lithium-ion batteries cannot meet actual needs. Metal lithium has high specific capacity (3860mAh / g) and low density (0.534g / cm 3 ) and good ductility, it has returned to the attention of researchers. However, whether used in liquid or solid-state batteries, metallic lithium will produce volume expansion, lithium dendrites, and dead lithium during the cycle process, thereby reducing the cycle coulombic efficiency and life of the metallic lithium electrode. More seriously, the continuous growth of dendrites may further cause safety issues (such as fire and explosion), which greatly limits the commercial application of metallic lithium anodes.

[0003] Currently, there are two main research areas regarding the application of metallic lithium anodes in solid-state batteries. First, a protective layer is placed on the surface of the metallic lithium anode to improve the interfacial compatibility between the metallic lithium and the solid electrolyte. For example, CN108461715A discloses a method for preparing a lithium anode for a solid-state battery. This method involves preparing an electrolyte solution with lithium salts, organic solvents, and electrolyte additives, and then electrochemically pre-circulating metallic lithium in the electrolyte to form a protective film on the surface of the metallic lithium anode. The resulting solid-state battery assembled with a metallic lithium anode is safe, stable, has high coulombic efficiency, and exhibits good interfacial compatibility between the metallic lithium and the solid electrolyte.

[0004] On the other hand, by introducing a nanoparticle interface layer on the surface of the metallic lithium, direct contact and reaction between the metallic lithium and the solid electrolyte can be prevented. For example, CN112703618A discloses an electrode for a solid-state lithium battery. The electrode comprises a current collector and an electrode active layer of lithium metal or a lithium metal alloy on the current collector. The lithium metal or lithium metal alloy has a surface layer of a homogeneous nano-alloy particle composition. The homogeneous nano-alloy particle composition contains nanoparticles of element M or nanoparticles of a lithium alloy of element M, where M is at least one element selected from Group 2 and Groups 8-16. The surface layer directly contacts the solid electrolyte, isolating the metallic lithium from the solid electrolyte and mitigating electrolyte decomposition.

[0005] However, the existing research on metallic lithium negative electrodes is limited to the interface between solid electrolytes and metallic lithium, which is a two-dimensional study. No in-depth research has been conducted on how to achieve interface stability of metallic lithium negative electrodes in the three-dimensional direction and solve problems such as uneven deposition and volume expansion of metallic lithium during charging and discharging.

[0006] Based on this, how to design a bipolar electrode with a stable interface in three-dimensional directions to overcome the above-mentioned shortcomings such as uneven deposition of metallic lithium, easy formation of dendrites, and volume expansion during charging and discharging has become an urgent problem to be solved at this stage. Summary of the Invention

[0007] In view of the problems existing in the prior art, the present application provides a bipolar electrode containing three-dimensionally distributed lithium fluoride and a preparation method thereof, wherein the electrode includes a lithium-carbon material layer composed of lithium-containing particles, carbon nanotubes and fluorinated carbon material, wherein the carbon nanotubes have dual transmission channels for ions and electrons, which can simultaneously regulate the current density and the transmission of lithium ions, overcoming the problems of uneven deposition of metallic lithium, which easily form dendrites and volume expansion during charging and discharging; the fluorinated carbon material and the lithium-containing particles can generate lithium fluoride in situ, and the lithium fluoride is the main component of SEI, which contributes to interface stability and uniform deposition of lithium, thereby improving the cycle stability of the electrode.

[0008] To achieve this goal, this application adopts the following technical solutions:

[0009] In a first aspect, the present application provides a bipolar electrode containing three-dimensionally distributed lithium fluoride, the electrode comprising a positive electrode active material layer, a current collector and a lithium-carbon material layer, the current collector being arranged between the positive electrode active material layer and the lithium-carbon material layer; wherein the lithium-carbon material layer comprises densely packed active substances, the active substances comprising lithium-containing particles, the surfaces of the lithium-containing particles being attached with carbon nanotubes, the carbon nanotubes being interwoven to form a three-dimensional porous skeleton, the surfaces of the lithium-containing particles, the surface of the three-dimensional porous skeleton or at least one position in the pores thereof being distributed with a fluorinated carbon material, and lithium fluoride is generated in situ between the fluorinated carbon material present on the surface of the lithium-containing particles and the lithium-containing core.

[0010] In this application, the carbon nanotubes in the lithium-carbon material layer are interwoven on the surface of the lithium-containing particles to form a three-dimensional porous framework, which can alleviate the volume expansion problem of the lithium-containing particles during the charge and discharge process in the three-dimensional direction. The carbon nanotubes serve as transmission channels for electrons and lithium ions, regulating the current density and lithium ion transmission in the three-dimensional direction to homogenize, thereby inhibiting the formation and growth of lithium dendrites. In addition, the three-dimensional porous framework formed by the carbon nanotubes provides support sites for the fluorinated carbon material, improves the conductivity of the fluorinated carbon material, and enables its stable and uniform distribution.

[0011] In the present application, the densely packed active material refers to a state in which the gaps between the lithium-containing particles are occupied by interwoven carbon nanotubes and / or carbon fluoride materials, forming a densely packed state.

[0012] In the present application, lithium fluoride and carbon are generated in situ between the fluorinated carbon material located on the surface of the lithium-containing particles and the lithium-containing core in the lithium-carbon material layer. The lithium fluoride makes the interfaces between the lithium-containing particles and the interfaces between the lithium-containing particles and the solid electrolyte more compatible and stable; the fluorinated carbon material located on the surface or pores of the three-dimensional porous skeleton reacts with active lithium to generate lithium fluoride and carbon during the charge and discharge cycle, which can increase the content of lithium fluoride in the SEI, continuously stabilize the interface, contribute to the uniform deposition of lithium, and inhibit the growth of lithium dendrites; carbon provides a transmission channel for electrons and / or lithium ions, regulates the uniform distribution of current density and the uniform deposition of metallic lithium, and inhibits the generation of lithium dendrites.

[0013] In the present application, carbon nanotubes and fluorinated carbon materials cooperate with each other to improve interface compatibility and stabilize the electrode interface without reducing the conductivity of the electrode. The bipolar electrode has excellent cycle performance. Compared with the metallic lithium negative electrode, the electrode of the present application converts the two-dimensional planar active lithium deposition / stripping mechanism into a three-dimensional mechanism. The internal interface of the electrode is stable in the three-dimensional direction, and the contact interface between the electrode and the solid electrolyte is also stable, which can achieve high-rate charge and discharge and has excellent rate performance.

[0014] Optionally, the lithium-containing particles include metallic lithium and / or lithium alloys, the alloying elements in the lithium alloy include at least one of tin, gold, barium, bismuth, calcium, germanium, platinum, lead, antimony, silver, boron, magnesium, indium, gallium, aluminum or zinc, and the content of metallic lithium in the lithium alloy is more than 50%, preferably more than 80%, and more preferably more than 90%.

[0015] Optionally, the average particle size of the lithium-containing particles is 1-100 μm, preferably 10-50 μm.

[0016] Optionally, the carbon nanotubes include at least one of single-walled carbon nanotubes, multi-walled carbon nanotubes, modified single-walled carbon nanotubes or modified multi-walled carbon nanotubes.

[0017] Optionally, the number of layers of the carbon nanotubes is less than or equal to 15 layers, preferably 1-10 layers.

[0018] Optionally, the outer diameter of the carbon nanotube is less than 30 nm, preferably 1-20 nm.

[0019] Optionally, the length of the carbon nanotubes is 0.5 μm to 50 μm, preferably 1-30 μm.

[0020] Optionally, the modified single-walled carbon nanotubes or modified multi-walled carbon nanotubes include but are not limited to at least one of carboxylated single-walled carbon nanotubes, carboxylated multi-walled carbon nanotubes, hydroxylated single-walled carbon nanotubes, hydroxylated multi-walled carbon nanotubes, amino-dated single-walled carbon nanotubes, amino-dated multi-walled carbon nanotubes, graphitized single-walled carbon nanotubes, graphitized multi-walled carbon nanotubes, copper-plated single-walled carbon nanotubes, copper-plated multi-walled carbon nanotubes, nickel-plated single-walled carbon nanotubes, nickel-plated multi-walled carbon nanotubes, nitrogen-doped single-walled carbon nanotubes, nitrogen-doped multi-walled carbon nanotubes, silver-doped single-walled carbon nanotubes or silver-doped multi-walled carbon nanotubes.

[0021] Optionally, based on the total mass of the lithium-carbon material layer being 100%, the mass fraction of the carbon nanotubes is 0.05-50%, preferably 0.25%-30%, and more preferably 0.5-20%.

[0022] Optionally, the fluorinated carbon material includes at least one of fluorinated graphite, fluorinated activated carbon, fluorinated carbon black, fluorinated carbon nanofibers, fluorinated graphene, fluorinated graphene oxide, or fluorinated carbon nanotubes;

[0023] Optionally, the size of the carbon fluoride material is 1 nm-50 μm, preferably the nano-scale carbon fluoride material has a size of 3 nm to 500 nm, more preferably 5-300 nm.

[0024] Optionally, the atomic ratio of carbon to fluorine in the fluorinated carbon material is greater than 0 and less than 1.25, for example, it can be 0.1, 0.25, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.1, 1.2 or 1.25, including but not limited to the listed point values. The atomic ratio can take into account both the in situ construction of a complete SEI and the regulation of electron transport, and is preferably 0.5-1.

[0025] Optionally, the mass ratio of the carbon nanotubes to the carbon fluoride material is 1:(0.1-100), preferably 1:(0.5-50), and more preferably 1:(1-20). The specific mass ratio of carbon nanotubes and carbon fluoride materials enables the bipolar electrode to have good cycle performance. The mass ratio can be 1:0.1, 1:0.3, 1:0.5, 1:0.8, 1:1, 1:2.5, 1:5, 1:10, 1:20, 1:30, 1:40, 1:50, 1:60, 1:75, 1:90 or 1:100, including but not limited to the listed point values. If the mass ratio is too large, there will be less carbon fluoride material, less lithium fluoride generated on the surface of the lithium-containing particles, and limited effect on interface regulation; if the mass ratio is too small, there will be less carbon nanotubes, and the volume expansion of the lithium-containing particles and the conductivity of the carbon fluoride material will be limited, and the effect of regulating the uniformity of lithium ions and current density will be poor.

[0026] It should be noted that the carbon fluoride material in the mass ratio of carbon nanotubes to carbon fluoride material, including the portion that reacts in situ with the lithium-containing core, is the total mass of the carbon fluoride material in the entire electrode.

[0027] Optionally, the thickness of the carbon fluoride material distribution area on the surface of the lithium-containing particles is 0.1-10 μm, preferably 0.5-5 μm. In the present invention, the thickness includes the lithium fluoride generated in situ by the contact reaction between the surface of the lithium-containing particles and the carbon fluoride material. Because the lithium-containing particles react with the contacted carbon fluoride material to generate lithium fluoride and carbon, the reaction is in situ. The generated lithium fluoride is difficult to distinguish from the carbon fluoride material on the surface of the lithium-containing particles that is not in contact, and therefore is included in the overall thickness.

[0028] Optionally, the positive electrode active material layer includes any one or a combination of at least two of lithium iron phosphate, lithium manganese iron phosphate, lithium nickel cobalt manganate, lithium nickel cobalt aluminum oxide, lithium manganate, lithium cobalt oxide, sublimated sulfur, sulfided polyacrylonitrile, vanadium pentoxide or MS2 (M = Fe, Mn, Mo, V, Ti, Co or Cr).

[0029] Optionally, the current collector includes a base current collector and a modified current collector, wherein the base current collector includes any one of copper foil, composite copper foil, aluminum foil, nickel foil, stainless steel foil, conductive polymer film, or carbon fiber, or a combination of at least two thereof. The polymer matrix material of the conductive polymer composite film includes, but is not limited to, at least one of polyethylene, polypropylene, polystyrene, polyurethane, epoxy resin, and phenolic resin. The conductive filler of the conductive polymer composite film includes, but is not limited to, at least one of conductive carbon black, conductive graphite, nano-carbon fiber, carbon nanotubes, graphene, metal, and metal oxide.

[0030] Optionally, the modified current collector includes a base current collector and a coating disposed on the surface of the base current collector, wherein the coating comprises any one of graphene, graphene oxide, chromate, manganese oxide, or aluminum oxide, or a combination of at least two. Different types of coatings interact differently with the lithium-carbon material layer, and preferably, a coating that forms an integral structure with the lithium-carbon material coating is selected based on actual needs, typically 3-10 μm.

[0031] In a second aspect, the present application provides a method for preparing the bipolar electrode as described in the first aspect above, the method comprising the following steps:

[0032] (1) mixing lithium-containing particles, a fluorinated carbon material, carbon nanotubes, and an organic solvent, and then spray-drying or high-speed dispersing at a rotation speed of 5000 rpm to remove the organic solvent to obtain a lithium-carbon material, wherein the organic solvent is inert to the lithium-containing particles;

[0033] (2) mixing the positive electrode active material, the conductive agent and the binder and placing them on one side of the current collector; or placing the lithium carbon material on one side of the current collector;

[0034] (3) Placing an active material layer having a polarity opposite to that in step (2) on the other side of the current collector to obtain the bipolar electrode.

[0035] The organic solvent includes, but is not limited to, any one or a combination of at least two of liquid alkanes with 5 to 10 carbon atoms, benzene, p-xylene, solvent oil D40, solvent oil D60, solvent oil D80, liquid paraffin or petroleum ether.

[0036] The lithium-containing particles include metallic lithium powder and / or lithium alloy powder.

[0037] As the preferred technical solution of this application, step (2) includes the following operations:

[0038] (a) preparing a positive electrode active material, a conductive agent, and a binder into a positive electrode active material layer through a dry process, and then placing it on one side of the current collector through a mechanical rolling and / or bonding process;

[0039] (b) placing the material containing lithium carbon material on the other side of the current collector in step (a) by mechanical rolling, twisting, spraying or stamping, or a combination of at least two of the above, to obtain the electrode structure;

[0040] or (a') placing the material containing the lithium-carbon material on one side of the current collector by mechanical rolling, twisting, spraying or stamping, or a combination of at least two thereof;

[0041] (b') preparing a positive electrode active material, a conductive agent and a binder into a positive electrode active material layer through a dry process, and then arranging it on the other side of the current collector through a mechanical rolling and / or bonding process to obtain the electrode structure.

[0042] In a third aspect, the present application provides a solid-state battery, comprising the bipolar negative electrode as described in the first aspect above.

[0043] Compared with the prior art, this application has at least one of the following beneficial effects:

[0044] (1) In the bipolar electrode provided by the present application, carbon nanotubes are exposed on the surface of the lithium-carbon material layer to form protrusions, which greatly increases the roughness of the lithium-carbon material layer, so that the lithium-carbon material layer is better combined with the solid electrolyte. At the same time, the skeleton formed exists in the entire lithium-carbon material layer phase, and the electrode structure is stable.

[0045] (2) The bipolar electrode provided by the present application has carbon nanotubes with dual ion and electron channels, which effectively regulate the electrode current density and the transmission of lithium ions, inhibit the growth of lithium dendrites, and the electrode has good cycle stability and excellent rate performance;

[0046] (3) The bipolar electrode provided by the present application has lithium fluoride and carbon fluoride material distributed in three dimensions. Lithium fluoride is an important component of SEI. During the charge and discharge process, the carbon fluoride material acts as a fluorine source and reacts with active lithium to continuously generate lithium fluoride. It has good compatibility with the solid electrolyte and can stabilize the interface between the negative electrode and the solid electrolyte, regulate the deposition of lithium, and inhibit the generation and growth of dendrites.

[0047] (4) This application uses carbon nanotubes and carbon fluoride materials to coordinate and control the electrode interface, designing parameters such as the mass ratio of specific carbon nanotubes and carbon fluoride materials and the type of carbon fluoride materials to further optimize the structural stability and electrochemical performance of the electrode;

[0048] (5) The preparation method provided in this application has a short process flow, high production efficiency, and universal applicability. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] Figure 1 Schematic diagram comparing the electrode in the prior art and the electrode of the present application during the charge and discharge process,

[0050] 1-metal lithium, 1'-lithium-carbon material layer without fluorinated carbon material, 1"-lithium-carbon material layer in this application, 11"-fluorinated carbon material, 2-current collector, 3-solid electrolyte layer, 4-positive electrode active material layer;

[0051] Figure 2 1 is the cycle test curve of Example 2, Example 3 and Example 4;

[0052] Figure 3 2 are the cycle test curves of Example 2, Comparative Example 1 and Comparative Example 2;

[0053] Figure 4 These are the cycle test curves of Example 2 and Comparative Examples 3-5. DETAILED DESCRIPTION

[0054] To facilitate understanding of the present application, the present application lists the following examples. Those skilled in the art should understand that the examples are only provided to help understand the present application and should not be considered as specific limitations of the present application.

[0055] For example, the bipolar electrode of the present application is different from the electrode 1 and the electrode 2 in the prior art in the negative electrode interface during the charge and discharge process, as shown in the comparative schematic diagram. Figure 1As shown. In the prior art, the negative electrode active material of electrode 1 is metallic lithium 1. During the charge and discharge process, voids or holes appear at the location where the surface of the metallic lithium 1 contacts the solid electrolyte 3, resulting in uneven current density on the surface of the metallic lithium negative electrode 1 and poor interface contact between the metallic lithium negative electrode 1 and the solid electrolyte 3. In the prior art, the lithium-carbon material layer 1' in electrode 2 contains only carbon nanotubes and no fluorinated carbon material. The carbon nanotubes' ability to recover deformation is utilized, adaptively changing with the volume of the metallic lithium and / or lithium alloy, ensuring that the lithium-carbon material layer 1' maintains good contact with the current collector 2 and the solid electrolyte layer 3 during the charge and discharge process. However, the interface stability is poor. The lithium-carbon material layer 1" of the electrode in the present application includes lithium-containing particles, carbon nanotubes and carbon fluoride materials. The carbon nanotubes are distributed on the surface of the lithium-containing particles and intertwined to form a three-dimensional porous skeleton. The carbon fluoride material 11" is distributed on the surface of the lithium-containing particles, on the surface of the three-dimensional porous skeleton or at least one position in the pores. Lithium fluoride is generated in situ between the carbon fluoride material 11" on the surface of the lithium-containing particles and the lithium-containing particles (lithium-containing core). The lithium fluoride is distributed in three dimensions, so that the interface stability of the electrode in the three-dimensional direction is good. The interface rich in lithium fluoride can regulate the uniform deposition of metallic lithium, inhibit the generation and growth of lithium dendrites, and has excellent cycle performance.

[0056] Example 1

[0057] This embodiment provides a bipolar electrode, which includes a copper-aluminum composite foil, wherein a lithium-carbon material layer with a thickness of 20 μm is provided on the copper foil side of the copper-aluminum composite foil, wherein the lithium-carbon material layer includes a densely packed active substance, wherein the active substance includes metallic lithium particles, wherein the surface of the metallic lithium particles has a three-dimensional porous skeleton formed by interweaving multi-walled carbon nanotubes, and fluorinated carbon black is distributed on at least one position on the surface of the metallic lithium particles, on the surface of the three-dimensional porous skeleton, or in the pores, and lithium fluoride is generated in situ between the fluorinated carbon black present on the surface of the metallic lithium particles and the metallic lithium particles; and a positive electrode active material layer with a thickness of 150 μm is provided on the aluminum foil side of the copper-aluminum composite foil, wherein the positive electrode active material layer includes lithium iron phosphate.

[0058] The preparation method of the electrode comprises the following steps:

[0059] (1) Multi-walled carbon nanotubes (Xianfeng Nano, XFM67, length 10-20 μm, outer diameter 4-

[0060] 6nm), fluorinated carbon black (Shanghai Furui Fine Chemical Co., Ltd., fluorine-carbon ratio 1.0, particle size 50-100nm), metallic lithium powder with an average particle size of 10μm and n-hexane were mixed at a rotation speed of 8000rpm for 15min, the mass ratio of multi-walled carbon nanotubes to fluorinated carbon black was 1:0.1, and the mass fraction of multi-walled carbon nanotubes in the lithium-carbon material was controlled to be 0.25%, filtered, and dried to obtain a lithium-carbon material;

[0061] (2) In a clean room with a dew point of -45°C, a lithium carbon material was spread between two layers of release films and mechanically rolled to form a foil. Then, one layer of the release film was peeled off to obtain a composite foil. The composite foil was mechanically rolled and composited onto the copper foil side of a 20 μm thick copper-aluminum composite foil (Desco Electronic Technology (Kunshan) Co., Ltd.), and the thickness of the lithium carbon material layer was 50 μm.

[0062] (3) A positive electrode mixture was prepared by combining lithium iron phosphate, an ionic conductor lithium lanthanum zirconium oxide (LLZTO), acetylene black, and PTFE in a mass ratio of 75:15:5:5. After high-speed shearing, the mixture was hot-pressed to obtain a positive electrode active material layer. The positive electrode active material layer was composited onto the aluminum foil side of a copper-aluminum composite foil in a clean room with a dew point of -45°C to obtain the electrode.

[0063] Example 2

[0064] This embodiment provides a bipolar electrode, which includes a stainless steel foil, a lithium-carbon material layer with a thickness of 50 μm provided on one side of the stainless steel foil, the lithium-carbon material layer including a densely packed active material, the active material including metallic lithium particles, the surface of the metallic lithium particles having a three-dimensional porous skeleton formed by interweaving single-walled carbon nanotubes, graphite fluoride distributed on the surface of the metallic lithium particles, on the surface of the three-dimensional porous skeleton, or at least one location in the pores, and lithium fluoride is generated in situ between the graphite fluoride present on the surface of the metallic lithium particles and the metallic lithium particles; a positive electrode active material layer with a thickness of 100 μm is provided on the aluminum foil side of the stainless steel foil, and the positive electrode active material layer comprises lithium nickel cobalt manganese oxide NCM811 coated with lithium niobate.

[0065] The preparation method of the electrode comprises the following steps:

[0066] (1) lithium niobate-coated lithium nickel cobalt manganese oxide NCM811, ionic conductor lithium lanthanum zirconium oxide LLZO, Ketjen black, single-walled carbon nanotubes, and binder polytetrafluoroethylene (PTFE) were mixed uniformly in a mass ratio of 75:15:4:1:5, subjected to high-speed shearing, and hot rolled to form a film layer, which was then rolled onto one side of a stainless steel foil with a thickness of 12 μm;

[0067] (2) Mixing a single-walled carbon nanotube dispersion (Okoshiel, with a diameter of 1 nm, a length of 5 μm, and 3 wt%), fluorinated graphite (Aladdin, F302204, with an F content of ≥56 wt.%, and D90 ≤8 μm), metallic lithium powder with an average particle size of 50 μm, and solvent oil D40, controlling the mass fraction of single-walled carbon nanotubes in the lithium-carbon material to be 30%, and the mass ratio of single-walled carbon nanotubes to fluorinated graphite to be 1:100, and spray drying to obtain a lithium-carbon material;

[0068] (3) In a clean room with a dew point of -45°C, a lithium carbon material was rolled onto the other side of a stainless steel foil. The thickness of the lithium carbon material layer was 50 μm, thereby obtaining the electrode.

[0069] Example 3

[0070] Compared with Example 2, the only difference is that the mass ratio of single-walled carbon nanotubes to graphite fluoride is replaced with 1:0.5, and the other conditions are the same.

[0071] Example 4

[0072] Compared with Example 2, the only difference is that the mass ratio of single-walled carbon nanotubes to graphite fluoride is replaced with 1:1, and the other conditions are the same.

[0073] Example 5

[0074] Compared with Example 2, the only difference is that the mass ratio of single-walled carbon nanotubes to graphite fluoride is replaced with 1:20, and the other conditions are the same.

[0075] Example 6

[0076] Compared with Example 2, the only difference is that the mass ratio of single-walled carbon nanotubes to graphite fluoride is replaced with 1:50, and the other conditions are the same.

[0077] Example 7

[0078] Compared with Example 2, the fluorinated graphite was replaced by fluorinated carbon black (Shanghai Furui Fine Chemical Co., Ltd., fluorine-carbon ratio 1.0, particle size 50-100 nm).

[0079] Example 8

[0080] Compared with Example 2, the metallic lithium powder was replaced with lithium-boron alloy particles (the mass fraction of boron was 1%).

[0081] Example 9

[0082] Compared with Example 2, the metallic lithium powder was replaced with lithium-tin-silver alloy particles (the mass fraction of tin was 7%, and the mass fraction of silver was 3%).

[0083] Comparative Example 1

[0084] Compared with Example 2, the only difference is that the lithium-carbon material layer is replaced by a metal lithium strip, and the other conditions are the same as those in Example 2.

[0085] Comparative Example 2

[0086] Compared with Example 2, the only difference is that the lithium-carbon material in the lithium-carbon material layer is replaced by a physical mixture of metallic lithium powder, single-walled carbon nanotubes and graphite fluoride (not the structure of this application, and the rotation speed in the preparation process is 2000 rpm), and the other conditions are the same as Example 2.

[0087] Comparative Example 3

[0088] Compared with Example 2, the only difference is that the lithium-carbon material layer contains only single-walled carbon nanotubes and does not contain fluorinated graphite.

[0089] Comparative Example 4

[0090] Compared with Example 2, the only difference is that the fluorinated graphite in the lithium-carbon material layer is replaced with ordinary graphite (purchased from CLUDE experimental consumables).

[0091] Comparative Example 5

[0092] Compared with Example 2, the only difference is that the lithium-carbon material layer contains only graphite fluoride but no single-walled carbon nanotubes.

[0093] Test data:

[0094] The electrodes in Examples 1-9 and Comparative Examples 1-5 were assembled into solid-state batteries for testing: the solid-state battery comprises the above-mentioned 1 bipolar electrode and 2 single-sided pole pieces with opposite polarity to the electrode, the solid electrolyte is Li6PS5Cl (LPSCl), and the cycle performance is tested under charge and discharge conditions of 60°C and 0.2C. The test external pressure is 60 MPa, and the cycle data are shown in Table 1.

[0095] Table 1 Test data of electrodes

[0096]

[0097] From Table 1 we can see that:

[0098] (1) Combining Example 2 and Examples 3-6, it can be seen that the solid-state battery cycle performance of Examples 3-6 is better than that of Example 2. This is because the mass ratio of the single-walled carbon nanotubes and the fluorinated graphite in Example 2 is relatively small and is not within the preferred range. The fluorinated graphite content is high and the conductivity is poor. The single-walled carbon nanotube content is low, and the effect of alleviating the volume expansion of metallic lithium is limited. At the same time, the effect of improving the conductivity of the fluorinated carbon material is weak. Combined with Figure 2It can be seen that the solid-state batteries of Examples 3 and 4 experienced capacity recovery during the test process. The solid-state battery of Example 3 experienced capacity recovery after 150 cycles, and the solid-state battery of Example 4 experienced capacity recovery after 220 cycles. This may be because during the cycle, the fluorinated graphite located on the surface or pores of the three-dimensional porous skeleton formed by the single-walled carbon nanotubes reacted with the active lithium to generate lithium fluoride and carbon, which increased the content of lithium fluoride in the SEI, continuously stabilized the interface, regulated the uniform deposition of metallic lithium, and improved the cycle performance of the electrode.

[0099] (2) Combining Examples 2 and 7, it can be seen that the solid-state battery cycle performance of Example 7 is better than that of Example 2. This is because the nano-scale fluorinated carbon material used in Example 7 has a better matching effect with the single-walled carbon nanotubes than the micron-scale fluorinated carbon material, is more evenly distributed in the lithium-carbon material, and is more conducive to stabilizing the interface;

[0100] (3) Based on Example 2 and Examples 8-9, it can be seen that the cycle performance of Examples 8-9 is better than that of Example 2. This is because lithium alloys are used in Examples 8 and 9, and the alloying elements can regulate the uniform deposition of metallic lithium during the charge and discharge process;

[0101] (4) Combining Example 2 with Comparative Examples 1 and 2, it can be seen that the cycle performance of Example 2 is better than that of Comparative Examples 1-2. This is because the specific structure and component design of the lithium-carbon material layer in Example 2 are better than those in Comparative Examples 1-2. Specifically, the selected single-walled carbon nanotubes are tubular carbon materials, which are exposed on the electrode surface to form protrusions, which greatly increase the roughness of the lithium-carbon material layer, so that the lithium-carbon material layer is better combined with the solid electrolyte, and a porous skeleton is formed in the entire lithium-carbon material layer, and the electrode structure is stable. The single-walled carbon nanotubes can simultaneously regulate ions and The transmission of electrons, while providing support for the fluorinated carbon material and improving the conductivity of the fluorinated carbon material, the fluorinated carbon material reacts with the active lithium to generate lithium fluoride and carbon, the SEI interface is rich in lithium fluoride, and the uniform deposition of metallic lithium is regulated, so that the electrode has excellent cycle performance; while Comparative Example 1 is only a metallic lithium belt, and the volume expansion and interface problems during the charge and discharge process are more prominent; although carbon nanotubes and fluorinated graphite are used in Comparative Example 2, the structure of the present application is not formed, which can stabilize the interface and alleviate the volume expansion to a certain extent, but the effect is worse than that of the structure of the present application; combined with Figure 3 The test curve also confirms the above analysis;

[0102] (5) From the perspective of Example 2 and Comparative Examples 3 to 5, it can be seen that the cycle performance of Example 2 is better than that of Comparative Examples 3 to 5. This is because Comparative Example 3 contains only single-walled carbon nanotubes and no fluorinated graphite, and only regulates the volume change of the lithium-carbon material layer during the cycle, which cannot improve the compatibility of the interface between the negative electrode and the solid electrolyte, and cannot stabilize the interface in three dimensions. The capacity decreases significantly, which is reflected in Figure 4The test curve in the figure; ordinary graphite is used in Comparative Example 4, which cannot play the role of fluorinated graphite in stabilizing the interface in the three-dimensional direction; in Comparative Example 5, only fluorinated graphite is used, and no single-walled carbon nanotubes are contained. Although it can stabilize the interface, it does not have the support of single-walled carbon nanotubes, so displacement will occur during the charge and discharge process, and the volume change control effect on the lithium-carbon material layer is weak, and the capacity decays rapidly, such as Figure 4 shown.

[0103] In summary, the electrode designed in this application has both three-dimensional interface stability and cycle stability, and is a bipolar electrode with excellent performance.

[0104] The applicant declares that while the above-mentioned embodiments are used to illustrate the detailed structural features of the present application, the present application is not limited to the above-mentioned detailed structural features, which does not mean that the present application must rely on the above-mentioned detailed structural features in order to be implemented. Those skilled in the art should understand that any improvements to the present application, equivalent replacements for selected components, additions of auxiliary components, and selection of specific methods, etc., fall within the scope of protection and disclosure of the present application.

Claims

1. A bipolar electrode containing three-dimensionally distributed lithium fluoride, characterized in that: The electrode comprises a positive electrode active material layer, a current collector and a lithium carbon material layer, wherein the current collector is arranged between the positive electrode active material layer and the lithium carbon material layer; The lithium-carbon material layer includes densely packed active substances, the active substances include lithium-containing particles, carbon nanotubes are attached to the surface of the lithium-containing particles, the carbon nanotubes are interwoven to form a three-dimensional porous skeleton, and carbon fluoride material is distributed on the surface of the lithium-containing particles, on the surface of the three-dimensional porous skeleton or at least one position in the pores, and lithium fluoride is generated in situ between the carbon fluoride material on the surface of the lithium-containing particles and the lithium-containing particles.

2. The bipolar electrode according to claim 1, wherein The lithium-containing particles include metallic lithium and / or lithium alloys, the alloying elements in the lithium alloy include at least one of tin, gold, barium, bismuth, calcium, germanium, platinum, lead, antimony, silver, boron, magnesium, indium, gallium, aluminum or zinc, and the content of metallic lithium in the lithium alloy is greater than 50%.

3. The bipolar electrode according to claim 1 or 2, characterized in that: The fluorinated carbon material comprises at least one of fluorinated graphite, fluorinated activated carbon, fluorinated carbon black, fluorinated carbon nanofibers, fluorinated graphene, fluorinated graphene oxide or fluorinated carbon nanotubes; Preferably, the atomic ratio of carbon to fluorine in the fluorinated carbon material is greater than 0 and less than 1.25, preferably 0.5-1; Preferably, the mass ratio of the carbon nanotubes to the carbon fluoride material is 1:(0.1-100), preferably 1:(0.5-50), and more preferably 1:(1-20).

4. The bipolar electrode according to any one of claims 1 to 3, characterized in that: The average particle size of the lithium-containing particles is 1-100 μm, preferably 10-50 μm; Preferably, the thickness of the carbon fluoride material distribution area on the surface of the lithium-containing particles is 0.1-10 μm, preferably 0.5-5 μm.

5. The bipolar electrode according to any one of claims 1 to 4, characterized in that: The carbon nanotubes include at least one of single-walled carbon nanotubes, multi-walled carbon nanotubes, modified single-walled carbon nanotubes or modified multi-walled carbon nanotubes; Preferably, the number of layers of the carbon nanotubes is less than or equal to 15 layers, preferably 1-10 layers; Preferably, the outer diameter of the carbon nanotubes is less than 30 nm, preferably 1-20 nm; Preferably, the length of the carbon nanotubes is 0.5 μm to 50 μm, preferably 1-30 μm; Preferably, based on the total mass of the lithium-carbon material layer being 100%, the mass fraction of the carbon nanotubes is 0.05-50%, preferably 0.25%-30%, and more preferably 0.5-20%.

6. The bipolar electrode according to any one of claims 1 to 5, characterized in that: The current collector includes a basic current collector and a modified current collector, wherein the basic current collector includes any one or a combination of at least two of copper foil, composite copper foil, nickel foil, stainless steel foil, conductive polymer film or carbon fiber; The modified current collector includes a base current collector and a coating disposed on a surface of the base current collector, wherein the coating includes any one of graphene, graphene oxide, chromate, manganese oxide, or aluminum oxide, or a combination of at least two thereof.

7. The bipolar electrode according to any one of claims 1 to 6, characterized in that: The positive electrode active material layer includes any one of lithium iron phosphate, lithium manganese iron phosphate, lithium nickel cobalt manganate, lithium nickel cobalt aluminum oxide, lithium manganate, lithium cobalt oxide, sublimated sulfur, sulfided polyacrylonitrile, vanadium pentoxide or MS2 (M = Fe, Mn, Mo, V, Ti, Co or Cr) or a combination of at least two thereof.

8. A method for preparing the bipolar electrode according to any one of claims 1 to 7, characterized in that: The method comprises the following steps: (1) mixing lithium-containing particles, a fluorinated carbon material, carbon nanotubes, and an organic solvent, and then spray-drying or high-speed dispersing at a rotation speed of 5000 rpm to remove the organic solvent to obtain a lithium-carbon material, wherein the organic solvent is inert to the lithium-containing particles; (2) mixing the positive electrode active material, the conductive agent and the binder and placing them on one side of the current collector; or placing the lithium carbon material on one side of the current collector; (3) Placing an active material layer having a polarity opposite to that in step (2) on the other side of the current collector to obtain the bipolar electrode.

9. The method according to claim 8, characterized in that Step (2) includes the following operations: (a) preparing a positive electrode active material, a conductive agent, and a binder into a positive electrode active material layer through a dry process, and then placing it on either side of the current collector through a mechanical rolling and / or bonding process; (b) placing a material containing lithium carbon material on the other side of the current collector by mechanical rolling, twisting, spraying or stamping, or a combination of at least two of them, to obtain the bipolar electrode.

10. A solid-state battery, characterized in that: The solid-state battery comprises the bipolar electrode according to any one of claims 1 to 7.

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