Negative pole piece, preparation method thereof and solid-state battery

Abstract

The invention relates to the technical field of solid-state battery negative pole pieces, in particular to a negative pole piece, a preparation method thereof and a solid-state battery. The negative pole piece comprises a porous metal current collector; the lithium-containing conductive layer is distributed on the surface and / or in holes of the porous metal current collector and comprises a conductive agent and lithium salt; and the nano-silver particles are modified on the surface of the lithium-containing conductive layer. According to the negative pole piece provided by the invention, a multi-stage skeleton structure is formed by the porous current collector, the lithium salt, the conductive agent particles and the silver nanoparticles, so that rich nucleation sites and sufficient deposition space are provided for deposition of lithium. The structure can effectively regulate and control lithium ion flow distribution, uniform deposition of lithium is realized, generation of dendritic crystals is fundamentally inhibited, and volume expansion stress in the deposition / stripping process is relieved.

Description

Technical Field

[0001] This invention relates to the field of solid-state battery negative electrode technology, and more specifically, to a negative electrode, its preparation method, and a solid-state battery. Background Technology

[0002] In the field of all-solid-state sulfide batteries (ASSBs), lithium-free or anode-free ASSBs are widely considered one of the most promising battery configurations due to their ability to simplify battery structure and improve energy density, showing significant application prospects in new energy storage, electric vehicles, and other fields. However, short cycle life and low coulombic efficiency pose several severe scientific and technological challenges to the commercial application of this technology. The core issue stems from the difficulty in controlling the deposition / stripping behavior of metallic lithium in a solid-state environment. (1) Interface contact failure and impedance surge problem: In rigid solid-state battery systems, repeated lithium deposition and stripping will produce significant volume changes. This change will cause mechanical separation of the deposited lithium and the sulfide solid electrolyte (SSE) interface, forming point contact or complete detachment, thereby generating huge contact impedance. As cycling progresses, the interface failure area continues to expand, and the interface resistance (ASR) increases exponentially, which is the primary cause of the sudden drop in battery capacity and eventual failure.

[0003] (2) Lithium dendrite growth and internal short circuit problems: The continuously deteriorating interfacial contact leads to extremely uneven ion flow distribution. Lithium ions tend to preferentially flow to areas with lower interfacial resistance, resulting in excessively rapid local lithium deposition rates in these areas, leading to the formation of lithium dendrites. Sulfide electrolytes (such as Li6PS5Cl, Li...) 10 GeP2S 12 The material is relatively soft and unstable to lithium. The growing lithium dendrites can easily pierce the electrolyte, causing an internal short circuit in the battery and posing a serious safety hazard.

[0004] (3) Kinetic and efficiency issues arising from the “lithium-free” configuration: In an anode-free battery, all lithium in the initial cycle comes from the cathode. During the first deposition, lithium needs to undergo a difficult nucleation process on the current collector surface, which usually has a very high nucleation overpotential. This not only causes huge energy loss, but the extremely low initial coulombic efficiency (ICE) also severely dissipates the limited cathode lithium source, resulting in the actual battery capacity being far lower than the theoretical value and the cycle life being greatly shortened.

[0005] (4) Limitations of existing improvement schemes: a. Three-dimensional porous current collectors (such as copper foam): Although they can provide deposition space and alleviate expansion, the simple physical structure cannot effectively guide the uniform nucleation of lithium, and its huge specific surface area will aggravate side reactions and form a thicker unstable interface layer. b. Surface modification (such as spraying Ag nanolayers): The modified layer prepared by traditional coating methods has weak bonding with the current collector and is prone to falling off and failing during cycling; and most of them are two-dimensional or shallow surface modifications, which cannot cope with the deep lithium deposition behavior. c. Pre-lithiation: Direct use of metallic lithium foil or lithium powder, which has extremely high activity, serious side reactions at the interface with sulfide electrolyte, and its harsh requirements for the assembly environment also significantly increase the manufacturing cost.

[0006] In view of this, the present invention is hereby proposed. Summary of the Invention

[0007] The primary objective of this invention is to provide a negative electrode sheet with a three-dimensional structure, comprising a porous current collector with a porous structure, a lithium-containing conductive layer distributed within or on the surface of the porous current collector, the lithium-containing conductive layer comprising a conductive agent and a lithium salt, and the surface of the lithium-containing conductive layer further modified with silver nanoparticles. The negative electrode sheet provided by this invention, with its multi-level framework structure composed of a porous current collector, lithium salt, conductive agent particles, and silver nanoparticles, provides abundant nucleation sites and ample deposition space for lithium deposition. This structure can effectively regulate the distribution of lithium-ion flow, achieve uniform lithium deposition, fundamentally suppress dendrite formation, and alleviate volume expansion stress during the deposition / stripping process.

[0008] The second objective of this invention is to provide a method for preparing the negative electrode sheet as described above, which provides omnidirectional guidance for lithium deposition from the nanometer to the micrometer scale, thereby synergistically achieving a battery negative electrode with low nucleation overpotential, uniform deposition and high interface stability.

[0009] A third objective of the present invention is to provide a solid-state battery comprising the negative electrode sheet as described above.

[0010] In order to achieve the above-mentioned objectives of the present invention, the following technical solution is adopted: In a first aspect, the present invention provides a negative electrode sheet, the negative electrode sheet comprising: Porous metal current collectors; and A lithium-containing conductive layer distributed on the surface and / or within the pores of the porous metal current collector, wherein the lithium-containing conductive layer comprises a conductive agent and a lithium salt; Nanoparticles of silver that are modified on the surface of the lithium-containing conductive layer.

[0011] Furthermore, the pore size of the porous current collector is 5-10 μm.

[0012] Further, the conductive agent includes at least one of Super P, acetylene black, Ketjen black, carbon fiber and carbon nanotubes; preferably, the particle size of the conductive agent is 1 nm to 100 μm.

[0013] Furthermore, the lithium salt includes at least one of lithium fluoride, lithium nitride, lithium iodide, and lithium difluorooxalate borate.

[0014] Furthermore, the mass ratio of the conductive agent to the lithium salt is 10-1:1.

[0015] Furthermore, the thickness of the lithium-containing conductive layer is 5-50 μm.

[0016] Secondly, the present invention provides a method for preparing the negative electrode sheet, comprising the following steps: (a) Obtain a porous current collector; (b) The conductive agent, lithium salt, binder and solvent are mixed to obtain a negative electrode slurry. The negative electrode slurry is coated on the surface of the porous current collector and penetrates into the pores. After drying, a lithium-containing conductive layer is obtained. (c) Immerse the dried electrode sheet from step (b) into a soluble Ag source solution, and immediately immerse it in an alkaline solution. The generated AgOH is extremely unstable and rapidly decomposes into Ag2O, which is further reduced by the reducing substances in the system into nano-silver particles to obtain the negative electrode sheet.

[0017] Furthermore, in step (b), the concentration of Ag in the soluble Ag source solution is 0.1-0.5 mol / L.

[0018] Further, in step (c), the immersion time in the soluble Ag source solution is 5-20 min, and the immersion time in the alkaline solution is 10-30 min.

[0019] Further, in step (c), the concentration of the alkaline solution is 0.1-0.5 mol / L.

[0020] Thirdly, the present invention provides a solid-state battery, comprising the negative electrode sheet as described above, or the negative electrode sheet prepared by the method described above.

[0021] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. Solve the problems of unstable interface contact and impedance growth: Improve the stability of the interface contact between the negative electrode and the solid electrolyte during lithium deposition / stripping, and reduce the interface impedance.

[0022] 2. Solving the problem of lithium dendrite growth: By introducing silver nanoparticles, the nucleation overpotential of lithium is significantly reduced, and uniform and planar deposition of lithium is achieved. This eliminates the driving force for dendrite growth from the source and inhibits the formation and growth of lithium dendrites in sulfide all-solid-state batteries.

[0023] 3. Overcoming the low initial efficiency of anode-less batteries: By pre-embedding lithium salt, an active lithium source is added to the battery, significantly improving the initial coulombic efficiency and reversible capacity, and extending the cycle life of anode-less or lithium-deficient all-solid-state batteries.

[0024] 4. Balancing high energy density and high safety: The amount of lithium salt used is far lower than that of traditional lithium foil, achieving "lithium depletion", which not only improves energy density but also avoids the processing and safety risks brought about by highly active lithium. Detailed Implementation

[0025] The technical solution of the present invention will be clearly and completely described below with reference to specific embodiments. However, those skilled in the art will understand that the embodiments described below are some embodiments of the present invention, but not all embodiments, and are only used to illustrate the present invention, and should not be regarded as limiting the scope of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall be followed. Where the manufacturers of reagents or instruments are not specified, they are all conventional products that can be purchased commercially.

[0026] A specific embodiment of the present invention provides a negative electrode sheet, the negative electrode sheet comprising: A porous metal current collector; and a lithium-containing conductive layer distributed on the surface and / or within the pores of the porous metal current collector, the lithium-containing conductive layer comprising a conductive agent and a lithium salt; and nano-silver particles modified on the surface of the lithium-containing conductive layer.

[0027] In this invention, lithium salts supplement the active lithium source, improve the initial coulombic efficiency and battery capacity, and to some extent improve the problem of unstable interface contact.

[0028] Silver nanoparticles: They undergo an alloying reaction with lithium to form Li-Ag alloys, which can significantly reduce the nucleation overpotential of lithium and promote uniform lithium nucleation; at the same time, Ag has excellent electronic conductivity, which enhances the charge transport capability of the interface.

[0029] Carbon particles: They have good electronic conductivity and affinity for lithium ions, and together with silver nanoparticles, they form a continuous ion / electron conduction network, ensuring high lithium ion mobility.

[0030] In summary, this structure can effectively regulate the distribution of lithium ion flow, achieve uniform lithium deposition, fundamentally suppress dendrite formation, and alleviate volume expansion stress during deposition / stripping.

[0031] In one specific embodiment, the pore size of the porous current collector is 5-10 μm, for example, any single value or a range of any two values ​​selected from 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, and 10 μm. Preferably, the porous current collector can be a metallic current collector, such as copper, titanium, or stainless steel. Preferably, the pore area of ​​the porous current collector is 10% to 50% of the total surface area.

[0032] As an example, the preparation of a porous current collector includes: taking a copper foil with a thickness of 10 μm, and using an ultraviolet laser drilling machine at a power of 15W and a scanning speed of 100 mm / s to prepare a porous copper current collector with an average pore size of about 8 μm.

[0033] In one specific embodiment, the conductive agent includes at least one of Super P, acetylene black, Ketjen black, carbon fiber, and carbon nanotubes; preferably, the particle size of the conductive agent is 1 nm to 100 μm, for example, any single value or a range of any two single values ​​among 1 nm, 10 nm, 50 nm, 100 nm, 200 nm, 500 nm, 700 nm, 800 nm, 1 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 20 μm, 30 μm, 40 μm, 50 μm, 60 μm, 70 μm, 80 μm, 90 μm, and 100 μm.

[0034] In one specific embodiment, the lithium salt includes at least one of lithium fluoride, lithium nitride, lithium iodide, and lithium difluorooxalate borate.

[0035] In one specific embodiment, the mass ratio of the conductive agent to the lithium salt is 10-1:1, for example, any ratio or a range of any two ratios from 10:1, 8:1, 5:1, 4:1, 3:1, 2:1, to 10:1.

[0036] In one specific embodiment, the thickness of the lithium-containing conductive layer is 5-50 μm, for example, any one value or a range of any two values ​​from 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 20 μm, 30 μm, 40 μm, and 50 μm.

[0037] A specific embodiment of the present invention provides a method for preparing a negative electrode sheet, comprising the following steps: (a) Obtain a porous current collector; (b) The conductive agent, lithium salt, binder and solvent are mixed to obtain a negative electrode slurry. The negative electrode slurry is coated on the surface of a porous current collector and penetrates into the pores. After drying, a lithium-containing conductive layer is obtained. (c) Immerse the dried electrode sheet from step (b) into a soluble Ag source solution, and immediately immerse it in an alkaline solution after taking it out. The generated AgOH is extremely unstable and quickly decomposes into Ag2O, which is further reduced in situ by reducing substances (such as carbon) in the system to form nano-silver particles, thus obtaining the negative electrode sheet.

[0038] Silver nanoparticles, with their extremely small size (typically tens of nanometers), can further fill the gaps between carbon particles and lithium powder. By controlling the reaction concentration and time, the loading and size of silver nanoparticles can be tuned to form a multi-level matched three-dimensional stacked framework structure with the current collector pore size (5-10 μm) and carbon particle size (micrometer scale). The core functions of silver nanoparticles are: ① serving as excellent lithium nucleation sites, significantly reducing the lithium nucleation energy barrier; ② forming Li-Ag alloys with lithium, guiding the lateral layered growth of lithium rather than vertical dendrite growth; ③ greatly improving the electronic conductivity of local areas.

[0039] In this invention, the solvents of the solutions are all non-aqueous solvents, preferably ethanol.

[0040] In one specific embodiment, the adhesive includes, but is not limited to, one or more of styrene-butadiene rubber, polyacrylic acid, and polyvinylidene fluoride. The solvent includes, but is not limited to, one or more of hexane, heptane, toluene, anisole, and N-methylpyrrolidone.

[0041] In one specific implementation, in step (b), the concentration of Ag in the soluble Ag source solution is 0.1-0.5 mol / L, for example, any one value or a range of any two values ​​among 0.1 mol / L, 0.2 mol / L, 0.3 mol / L, 0.4 mol / L, and 0.5 mol / L.

[0042] In one specific implementation, in step (c), after immersion in the soluble Ag source solution, the sample is not immediately removed but requires a certain reaction time, such as 5-20 minutes, including any value or a range of any two values ​​from 5 minutes, 10 minutes, 15 minutes, and 20 minutes. Similarly, immersion in the alkaline solution requires a certain time, such as 10-30 minutes, including any value or a range of any two values ​​from 10 minutes, 15 minutes, 20 minutes, 25 minutes, and 30 minutes.

[0043] In one specific embodiment, in step (c), the concentration of the alkaline solution is 0.1-0.5 mol / L, for example, any single value or a range of any two values ​​from 0.1 mol / L, 0.2 mol / L, 0.3 mol / L, 0.4 mol / L, and 0.5 mol / L. Preferably, the alkaline solution can be an ethanol solution of KOH.

[0044] Step (c) is followed by a cleaning and drying process. For example, the electrode can be rinsed several times with ethanol and then vacuum dried at 60-110°C for 8-12 hours to obtain the final negative electrode.

[0045] One specific embodiment of the present invention provides a solid-state battery, including the negative electrode sheet as described above, or the negative electrode sheet prepared by the method described above. It also includes a solid electrolyte and a positive electrode sheet. This composite negative electrode structure can achieve low and stable interfacial impedance, significantly extend the cycle life of an anode-free all-solid-state battery, and improve rate performance and capacity retention.

[0046] Preferably, the solid-state battery is a sulfide all-solid-state battery, which solves the problem that lithium dendrites growing in sulfide electrolytes, due to their soft texture and instability to lithium, can easily pierce the electrolyte and cause internal short circuits. However, this negative electrode can also be used in solid-state batteries with other electrolytes.

[0047] Example 1 This embodiment provides a method for preparing a negative electrode sheet, specifically including: (1) Preparation of porous current collectors: A porous copper current collector with an average pore size of about 8 μm was prepared by using a 10 μm thick copper foil and a UV laser drilling machine at a power of 15 W and a scanning speed of 100 mm / s.

[0048] (2) Slurry preparation and coating: 90 mg of lithium LiF salt, 900 mg of conductive carbon particles (VGCF), and 100 mg of PVDF binder were weighed and mixed with 2 g of NMP solvent. The mixture was stirred in a planetary mixer for 4 hours to form a homogeneous slurry. The slurry was coated onto a porous copper current collector using a scraper with a 60 μm gap. The coated electrode was then transferred to a vacuum oven at 100°C and dried for 12 hours to obtain a lithium-containing conductive layer.

[0049] (3) Silver nanoparticle deposition: The electrode with the lithium-containing conductive layer was immersed in a 0.1 mol / L AgNO3 ethanol solution for 10 minutes. After removal, it was immediately immersed in an ethanol solution containing 0.1 mol / L KOH and gently stirred for 30 minutes. Subsequently, the electrode was rinsed several times with ethanol and vacuum dried at 60 °C for 10 hours to obtain the negative electrode.

[0050] Example 2 Compared with Example 1, the improvement of Example 2 is that in step (1), the pore diameter of the porous current collector is 5 μm.

[0051] Example 3 Compared with Example 1, the improvement of Example 3 is that in step (2), the lithium salt is Li3N.

[0052] Example 4 Compared with Example 1, the improvement of Example 4 is that in step (2), the conductive particles are acetylene black.

[0053] Example 5 Compared with Example 1, the improvement of Example 5 is that in step (2), 165 mg LiF + 825 mg conductive carbon particles VGCF are used.

[0054] Example 6 Compared with Example 1, the improvement of Example 6 is that in step (2), 3g of NMP solvent is used for mixing.

[0055] Example 7 Compared with Example 1, the improvement of Example 7 is that in step (2), a 100 μm scraper is used for slurry coating.

[0056] Example 8 Compared with Example 1, the improvement of Example 8 is that in step (3), the concentration of AgNO3 solution is 0.5 mol / L and the concentration of KOH ethanol solution is 0.5 mol / L.

[0057] Comparative Example 1 Compared to Example 1, Comparative Example 1 uses unperforated copper foil as the current collector.

[0058] Comparative Example 2 Compared to Example 1, Comparative Example 2 uses copper foil with only 10μm perforations.

[0059] Comparative Example 3 Compared to Example 1, no lithium salt was added to the slurry in step (2) of Comparative Example 3.

[0060] Comparative Example 4 Compared to Example 1, Comparative Example 4 had no step (3), i.e. no nano-silver was deposited on the surface.

[0061] Experimental Example 1 Electrolyte was weighed in a glove box and placed in a mold to be pressed into a sheet under a pressure of 500 MPa. Then, the negative electrode sheets obtained in Examples 1-8 and Comparative Examples 1-4 were laid flat under the electrolyte sheet. About 30 mg of positive electrode powder was added to the top of the electrolyte sheet and flattened. A positive current collector aluminum foil was then placed on top. The battery was pressed under a pressure of 500 MPa to obtain a testable battery.

[0062] Battery testing methods The test pressure for the mold battery was 20 MPa, and the cutoff voltage was 2.5~4.25 V. It was first charged and discharged at a rate of 0.1 C for 2 cycles, and then charged and discharged at a rate of 0.5 C until short circuit. The number of cycles when the capacity retention rate was 80% and the number of short circuit cycles of the battery were recorded. The data are shown in Table 1.

[0063] Table 1. Number of cycle cycles when battery capacity retention is 80% and number of cycle cycles when battery is short-circuited.

[0064] A comparison of the examples and comparative examples reveals that the anode using a three-layer composite structure of "silver nanoparticles-lithium salt-porous current collector and porous framework" significantly improves the battery's cycle performance and charge-discharge stability. This is attributed to the synergistic effect of the three-layer composite structure. The porous current collector forms the basis for the three-dimensional framework, effectively suppressing volume expansion and providing initial space for lithium deposition. The carbon particles, with their excellent electronic conductivity, construct the conductive framework, while the lithium salt supplements the lithium source, compensating for the irreversible capacity loss during the first cycle. The lithium salt and carbon particles together fill the porous structure, forming a preliminary lithium-ion storage and conduction matrix. The silver nanoparticles not only significantly reduce the lithium nucleation energy barrier but also form a Li-Ag alloy with lithium, guiding the lateral layered growth of lithium rather than vertical dendrite growth. The synergistic effect of the three-layer composite structure enhances the anode's performance.

[0065] Although the present invention has been illustrated and described with specific embodiments, it should be understood that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; those skilled in the art should understand that modifications can be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein, without departing from the spirit and scope of the present invention; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention; therefore, this means that all such substitutions and modifications that fall within the scope of the present invention are included in the appended claims.

Claims

1. A negative electrode sheet, characterized by, The negative electrode sheet includes: Porous metal current collectors; and A lithium-containing conductive layer distributed on the surface and / or within the pores of the porous metal current collector, wherein the lithium-containing conductive layer comprises a conductive agent and a lithium salt; Nanoparticles of silver that are modified on the surface of the lithium-containing conductive layer.

2. The negative electrode sheet according to claim 1, characterized by The pore size of the porous current collector is 5-10 μm.

3. The negative electrode sheet according to claim 1, wherein The conductive agent includes at least one of Super P, acetylene black, Ketjen black, carbon fiber, and carbon nanotubes; preferably, the particle size of the conductive agent is 1 nm to 100 μm. and / or; The lithium salt includes at least one of lithium fluoride, lithium nitride, lithium iodide, and lithium difluorooxalate borate.

4. The negative electrode sheet according to claim 1 or 3, characterized by, The mass ratio of the conductive agent to the lithium salt is 10-1:

1.

5. The negative electrode sheet according to claim 1, characterized in that, The thickness of the lithium-containing conductive layer is 5-50 μm.

6. The method for preparing the negative electrode sheet according to any one of claims 1-5, characterized in that, Includes the following steps: (a) Obtain a porous current collector; (b) The conductive agent, lithium salt, binder and solvent are mixed to obtain a negative electrode slurry. The negative electrode slurry is coated on the surface of the porous current collector and penetrates into the pores. After drying, a lithium-containing conductive layer is obtained. (c) Immerse the dried electrode sheet from step (b) into a soluble Ag source solution, and immediately immerse it in an alkaline solution after removing it. The generated AgOH is extremely unstable and rapidly decomposes into Ag2O, which is further reduced by the reducing substances in the system into nano-silver particles to obtain the negative electrode sheet.

7. The method for preparing the negative electrode sheet according to claim 6, characterized in that, In step (c), the concentration of Ag in the soluble Ag source solution is 0.1-0.5 mol / L.

8. The method for preparing the negative electrode sheet according to claim 6, characterized in that, In step (c), the immersion time in the soluble Ag source solution is 5-20 min, and the immersion time in the alkaline solution is 10-30 min.

9. The method for preparing the negative electrode sheet according to claim 6, characterized in that, In step (c), the concentration of the alkaline solution is 0.1-0.5 mol / L.

10. A solid-state battery, comprising a negative electrode sheet as described in any one of claims 1-5, or a negative electrode sheet prepared by the method for preparing a negative electrode sheet as described in any one of claims 6-9.

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