Composite anode for all-solid-state lithium-ion batteries and method for producing the same, all-solid-state lithium-ion batteries

Abstract

The application relates to a composite negative electrode for a full-solid-state lithium ion battery and a preparation method thereof. The composite negative electrode comprises, in parts by mass, 50-75 parts of a silicon-carbon composite active material, 20-40 parts of a sulfide solid electrolyte, 0.5-6 parts of acetylene black, and 2-5 parts of a binder; wherein the specific surface area of the acetylene black is 45-900 m 2 / g, the surface defect degree characterized by D / G is <1.8, and the particle size D50 of the sulfide solid electrolyte is 0.5-2.0 mu m. The application realizes the dual design of a low-defect nano-acetylene black material and a sulfide solid electrolyte particle size, reduces the side reaction of the negative electrode conductive agent and the electrolyte, guarantees the sufficient transmission of electrons and ions, and improves the kinetics and long-term stability.

Description

Technical Field

[0001] This application relates to the field of lithium-ion batteries, and more particularly to a composite negative electrode for all-solid-state lithium-ion batteries and a method for preparing the same, wherein the all-solid-state lithium-ion battery is described above. Background Technology

[0002] Silicon, with its extremely high theoretical lithium intercalation specific capacity (up to 4200 mAh / g) and low lithium storage potential, can achieve higher battery capacity and smaller battery volume than graphite anodes, making it one of the ideal candidates for new high-capacity lithium storage materials. Currently, to address the volume expansion problem of silicon electrode materials, novel silicon-carbon materials are increasingly being used. However, due to its porous hard carbon substrate and nearly half-silicon content, its intrinsic electronic conductivity is significantly lower than that of traditional graphite anodes. Therefore, it is necessary to adjust the electrode composition to promote the kinetics of silicon-carbon materials. However, while using excessive conductive agents and sulfide electrolytes can provide rapid kinetics, the contact between the conductive agent and the sulfide electrolyte during reduction at the negative electrode induces side reactions. This not only consumes active lithium but also generates an unstable SEI film, increasing cell impedance and significantly reducing cycle stability. On the other hand, in order to create more contact between the negative electrode and the electrolyte and to give the negative electrode system sufficient ion transport capacity, electrolyte materials with smaller particle sizes (D50 < 500 nm) and higher content are usually preferred. However, smaller particle sizes and more electrolytes also result in more surface area for the formation of SEI films with conductive agents and main material particles, increasing active lithium consumption and cell impedance, and also increasing the difficulty of dispersing electrolyte and conductive agent materials.

[0003] Therefore, there is a need for an improved composite anode for all-solid-state lithium-ion batteries and its preparation method. Summary of the Invention

[0004] The following is an overview of the subject matter described in detail herein. This overview is not intended to limit the scope of protection of this application.

[0005] In one aspect, this application provides a composite negative electrode for all-solid-state lithium-ion batteries, comprising, by weight, 50-75 parts of silicon-carbon composite active material, 20-40 parts of sulfide solid electrolyte, 0.5-6 parts of acetylene black, and 2-5 parts of binder; wherein the acetylene black has a specific surface area of ​​45-900 m². 2 / g, with a surface defect degree <1.8 as characterized by D / G; the particle size D50 of the sulfide solid electrolyte is 0.5-2.0μm.

[0006] In an exemplary embodiment, the composite negative electrode comprises, by weight, 55-70 parts of silicon-carbon composite active material, 25-35 parts of sulfide solid electrolyte, 0.5-6 parts of acetylene black and 4-5 parts of binder.

[0007] In an exemplary embodiment, the specific surface area of ​​the acetylene black is 100-800 m². 2 / g, surface defect degree characterized by D / G ≤1.6; and / or The particle size D50 of the sulfide solid electrolyte is 0.5-1 μm.

[0008] In an exemplary embodiment, the sulfide solid electrolyte is selected from Li6PS5Cl, Li3PS4, and Li 10 GeP2S 12 Li 10 SiP2S 12 Li 10 SnP2S 12 One or more of them.

[0009] In an exemplary embodiment, the sulfide solid electrolyte has a room temperature conductivity of 2-6 mS / cm.

[0010] In an exemplary embodiment, the silicon-carbon composite active material is selected from one of vapor-deposited silicon-carbon, carbon-coated porous silicon, carbon-coated nano-silicon, and carbon-coated silicon suboxide.

[0011] In an exemplary embodiment, the adhesive is selected from one or more of hydrogenated nitrile rubber styrene-butadiene copolymer, acrylate polymers, hydrogenated nitrile rubber, and fluoropolymers.

[0012] In an exemplary embodiment, the composite negative electrode further includes 20-120 parts of an additive; the additive is selected from one or more of isobutyl isobutyrate and isoamyl isovalerate.

[0013] On the other hand, this application provides a method for preparing the above-mentioned composite negative electrode, the method comprising mixing and grinding a silicon-carbon composite active material, a sulfide solid electrolyte, acetylene black and a binder to obtain a mixed slurry; coating the mixed slurry onto a current collector to obtain a negative electrode sheet; and drying the negative electrode sheet at 70°C-100°C to obtain the composite electrode.

[0014] In an exemplary embodiment, grinding may include ball milling at 100-500 rpm for 1-3 hours.

[0015] In an exemplary embodiment, isobutyl isobutyrate may be optionally added to the mixed slurry to give the mixed slurry a solid content of 40wt%-65wt%.

[0016] On the other hand, this application provides an all-solid-state lithium-ion battery, including a composite negative electrode, a sulfide solid electrolyte, and a positive electrode prepared by the above-described method or by the above-described method.

[0017] In this application, the D / G ratio refers to the fact that in the Raman spectra of carbon materials (such as graphite, graphene, carbon nanotubes, amorphous carbon, acetylene black, etc.), the D peak and G peak are the two most critical Raman characteristic peaks, reflecting the structural order and bonding properties of the material, respectively. The D peak is typically located at ~1350 cm⁻¹. -1 The D peak intensity is caused by defects in carbon materials, such as edges, vacancies, and doping, and reflects the defect density of the material. The more defects, the higher the D peak intensity; the G peak is typically around 1580 cm⁻¹. -1 Near the surface, these are stretching vibrations attributed to the carbon atom plane and are related to the degree of graphitization. The D / G ratio represents the intensity relationship between these two peaks and is used to assess the crystallinity quality of carbon materials. A larger ratio indicates more defects in the carbon atom crystal. Measurements are typically performed using Raman spectroscopy with a 532 nm laser, employing a surface scanning method, taking 100 points within a 100µm x 100µm interval to calculate the average value.

[0018] This application employs a dual design of low-defect nano-acetylene black material and sulfide solid electrolyte particle size to reduce side reactions between the conductive agent and electrolyte on the negative electrode side, while ensuring sufficient electron and ion transport, thereby improving kinetics and long-term stability.

[0019] This invention constructs a rapid electronic and ionic conduction pathway by using a specific combination of low-defect nano-acetylene black and suitable electrolyte particle size and addition amount, thereby achieving a fast kinetic and low lithium consumption anode system.

[0020] Other features and advantages of this application will be set forth in the following description, and will be apparent in part from the description, or may be learned by practicing the application. Other advantages of this application may be realized and obtained by means of the methods described in the description. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of this application clearer, the embodiments of this application are described in detail below. It should be noted that, unless otherwise specified, the embodiments and features described in these embodiments can be arbitrarily combined with each other.

[0022] This application provides a method for preparing a composite negative electrode, comprising mixing and grinding a silicon-carbon composite active material, a sulfide solid electrolyte, acetylene black and a binder to obtain a mixed slurry; coating the mixed slurry onto a current collector to obtain a negative electrode sheet; and drying the negative electrode sheet at 70℃-100℃ to obtain a composite electrode.

[0023] Unless otherwise specified, all materials used in the following examples and comparative examples are commercially available.

[0024] The methods for preparing the composite electrodes in the embodiments and comparative examples of this application can be described by the following steps: (1) Weigh each component in the glove box and place it in the ball mill jar, and add isobutyl isobutyrate to adjust the solid content; (2) Transfer the ball mill jar to a ball mill and ball mill at 300 rpm for 1 hour to obtain a uniform mixed slurry; (3) The mixed slurry is coated onto the current collector (such as copper foil) and dried at 80°C to obtain the composite negative electrode.

[0025] Tables 1 and 2 below list the amounts and parameter characteristics of each component in the embodiments and comparative examples of this application. Comparative Example 3 uses only acetylene black with parameters specific to this application; Comparative Example 4 uses only sulfide electrolyte with a specific particle size of this application; Comparative Example 5 uses a combination of furnace black with a specific surface area and D / G defined by this application and a sulfide electrolyte with a specific particle size of this application, wherein BET = 60 m... 2 Furnace black with a density of 2.5 g / g and a D / G ratio of 2.5 was subjected to high-temperature treatment, which reduced its D / G ratio to 1.7.

[0026] Table 1 Characterization parameters of acetylene black and sulfide electrolyte in the composite negative electrode in the embodiments and comparative examples of this application. * indicates that this furnace black has undergone calcination treatment to achieve this BET and D / G ratio.

[0027] Table 2. Amounts of each component (by mass) of the composite negative electrode in the embodiments and comparative examples of this application. Performance testing: The composite electrodes prepared in each embodiment and comparative example were assembled with LPSC solid electrolyte (Li6PS5Cl) and NCM 811 cathode material to form all-solid-state lithium-ion batteries and their electrochemical performance was tested. The test results are shown in Table 3 below.

[0028] The LPSC solid electrolyte used in battery testing and the LPSC solid electrolyte used in the composite anode can be the same material, such as having the same particle size. However, the LPSC solid electrolyte used in battery testing and the LPSC solid electrolyte used in the composite anode can also be different LPSC solid electrolytes.

[0029] The test conditions are as follows: Rate of activation: After activating with a current of 0.1C for 2 cycles, the rate of activation is then tested at 0.2C and 0.5C for 2 cycles each. Test voltage range: 0.005-1.5 V (vs. Li). + / Li), the test pressure is 60MPa.

[0030] Charge transfer impedance: EIS test was performed after activation with a current of 0.1C for 2 cycles, with an amplitude of 5 mV and a frequency of 0.01-1000000Hz; 0.1C Cycle Retention Rate: Current 0.1C, Test Voltage Range 0.005-1.5 V (vs. Li + / Li), the test pressure is 60MPa.

[0031] Table 3 The acetylene black used in this application is prepared through an acetylene pyrolysis process at a pyrolysis temperature exceeding 2000℃. Therefore, its graphitization degree is higher than that of furnace black, and its defect ratio (D / G) is generally less than 1.8. Thus, with the same addition amount and the same specific surface area, compared to furnace black conductive agents, using acetylene black conductive agents with low defect ratios will help reduce side reactions, not only weakening the increase in impedance but also reducing the consumption of active lithium.

[0032] The composite anode of this application includes acetylene black with high specific surface area and low defect degree, which constructs a high-efficiency and low-lithium-consumption electronic conduction network in the silicon-based electrode; at the same time, with the optimization of the particle size and content of the sulfide solid electrolyte, a fast ion conduction network is constructed while reducing side reactions with carbon materials.

[0033] As shown in Table 3, when the negative electrode is prepared using the acetylene black and sulfide electrolyte particles with the specific parameters of this application, the degree of side reactions of the negative electrode sheet is effectively suppressed, and the first-efficiency and cycle ratio are significantly improved. In particular, the retention rate is around 70% after 100 cycles, while the ratio is below 55%. At the same time, the kinetics of the negative electrode are also better due to the reduction of surface side reactions and the rapid transport of electrons and ions. At 0.5C, the retention rate is above 50%.

[0034] Comparative Example 4 uses a combination of acetylene black without the specific parameters of this application but with the specific particle size of the sulfide electrolyte of this application. Due to its extremely high specific surface area, it is difficult to disperse evenly during the corresponding slurry coating process to form the electrode, resulting in insufficient subsequent electrochemical kinetics.

[0035] Comparative Example 5 used furnace black with the specific surface area and D / G specified in this application (for BET=60 m). 2 The furnace black (with a D / G ratio of 2.5) was subjected to high-temperature treatment to reduce its D / G to 1.7, and this is a combination of a sulfide electrolyte with a specific particle size as described in this application. During the high-temperature treatment, as the D / G of the furnace black decreased, its agglomeration intensified, resulting in poor dispersion during subsequent slurry coating, thus degrading the performance of batteries, including those with negative electrodes made from it.

[0036] Although embodiments of this application have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting this application. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of this application.

Claims

1. A composite negative electrode for all-solid-state lithium-ion batteries, characterized in that, By weight, the composite negative electrode comprises 50-75 parts of silicon-carbon composite active material, 20-40 parts of sulfide solid electrolyte, 0.5-6 parts of acetylene black, and 2-5 parts of binder; wherein the specific surface area of ​​the acetylene black is 45-900 m². 2 / g, with a surface defect degree <1.8 as characterized by D / G; the particle size D50 of the sulfide solid electrolyte is 0.5-2.0μm.

2. The composite negative electrode according to claim 1, characterized in that, By weight, the composite negative electrode comprises 55-70 parts of silicon-carbon composite active material, 25-35 parts of sulfide solid electrolyte, 0.5-6 parts of acetylene black and 4-5 parts of binder.

3. The composite electrode according to claim 1 or 2, characterized in that, The specific surface area of ​​the acetylene black is 100-800 m². 2 / g, surface defect degree characterized by D / G ≤1.6; and / or The particle size D50 of the sulfide solid electrolyte is 0.5-1 μm.

4. The composite electrode according to claim 1 or 2, characterized in that, The sulfide solid electrolyte is selected from Li6PS5Cl, Li3PS4, and Li 10 GeP2S 12 Li 10 SiP2S 12 Li 10 SnP2S 12 One or more of them.

5. The composite electrode according to claim 4, characterized in that, The sulfide solid electrolyte has a room temperature conductivity of 2-6 mS / cm.

6. The composite electrode according to claim 1 or 2, characterized in that, The silicon-carbon composite active material is selected from one of the following: vapor-deposited silicon-carbon, carbon-coated porous silicon, carbon-coated nano-silicon, and carbon-coated silicon suboxide; and / or, The adhesive is selected from one or more of hydrogenated nitrile rubber styrene-butadiene copolymer, acrylate polymer, hydrogenated nitrile rubber, and fluoropolymer.

7. The composite electrode according to claim 1 or 2, characterized in that, The composite negative electrode also includes 20-120 parts of an additive; the additive is selected from one or more of isobutyl isobutyrate and isoamyl isovalerate.

8. A method for preparing a composite negative electrode according to any one of claims 1-7, characterized in that, The method includes mixing and grinding a silicon-carbon composite active material, a sulfide solid electrolyte, acetylene black, and a binder to obtain a mixed slurry; coating the mixed slurry onto a current collector to obtain a negative electrode sheet; and drying the negative electrode sheet at 70℃-100℃ to obtain the composite electrode.

9. The method according to claim 8, characterized in that, Optionally, isobutyl isobutyrate may be added to the mixed slurry to give the mixed slurry a solid content of 40wt%-65wt%.

10. A fully solid-state lithium-ion battery, characterized in that, The composite negative electrode, sulfide solid electrolyte, and positive electrode are prepared by any one of claims 1-7 or by the method described in claim 8 or 9.

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