Preparation method of double-layer structure nanosilicon-based negative electrode and sulfide all-solid-state battery

Abstract

The application belongs to the technical field of lithium ion batteries, and specifically discloses a preparation method of a double-layer structure nanometer silicon-based negative electrode and a sulfide full solid-state battery, which comprises the following steps: (1) high-temperature melting of nanometerized silicon powder and metal lithium at a certain ratio to prepare a lithium silicon alloy; (2) coating the prepared lithium silicon alloy on a current collector; (3) mixing nanometerized silicon powder and a binder, and covering the mixture on the surface of the coated lithium silicon alloy by using a dry method or a wet method process to obtain a double-layer structure full active silicon-based negative electrode; and (4) assembling the dry positive electrode, an electrolyte film and the double-layer structure nanometer silicon-based negative electrode into a soft package battery. Compared with a pure silicon negative electrode, the double-layer structure nanometer silicon-based negative electrode prepared by the application has higher electronic conductivity, higher specific capacity and better cycle stability, and the preparation process is simple, and the double-layer structure nanometer silicon-based negative electrode can be applied to a soft package battery based on a sulfide electrolyte film, and is suitable for practical application and large-scale production.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of lithium ion batteries, and particularly relates to a preparation method of a double-layer structure nanosilicon-based negative electrode and a sulfide full-solid-state battery. BACKGROUND

[0002] As a kind of lithium ion battery, all-solid-state lithium-ion battery (ASSB) uses solid electrolyte to replace organic electrolyte, and has multiple advantages such as high safety, high energy density and low cost, and is expected to be used in future electric vehicles and large-scale energy storage. However, compared with the positive electrode, the negative electrode of the current solid-state battery has more uncertainties. Intercalation type (such as graphite), high-energy alloy type material (such as Si) and lithium metal negative electrode are the main representative negative electrode materials of ASSB. Among them, Si has a theoretical specific capacity of 3590 mAh g -1 at room temperature, which is 10 times higher than that of the graphite negative electrode, close to the theoretical specific capacity of lithium metal, and has low lithium dendrite growth risk, and is a very promising negative electrode material. However, the problems of poor initial coulomb efficiency, large volume change (>300%) during cycling, low ion / electron conductivity and rapid capacity decay need to be solved. SUMMARY

[0003] The main purpose of the application is to provide a preparation method of a double-layer structure nanosilicon-based negative electrode and its application route in a sulfide full-solid-state battery, which aims to maximize the content of negative electrode active material while solving the problems of poor electronic conductivity, large volume change during cycling and rapid capacity decay of the existing pure silicon negative electrode, and providing a route for the scale-up and practical application of sulfide full-solid-state soft-pack batteries.

[0004] To achieve the above purpose, the application provides a preparation method of a double-layer structure nanosilicon-based negative electrode, which comprises the following steps:

[0005] (1) melt nanosilicon powder and lithium in a certain proportion at high temperature to prepare lithium-silicon alloy, wherein the H2O and O2 content during preparation is required to be less than 1 ppm, the melting temperature is 200-350℃, and the melting time is 1-6h;

[0006] (2) mix the prepared lithium-silicon alloy with a binder and coat it on a current collector;

[0007] (3) mix nanosilicon powder with a binder, and coat it on the surface of the coated lithium-silicon alloy to obtain a double-layer structure nanosilicon-based negative electrode.

[0008] Preferably, the nanosilicon powder in step (1) and (3) is nanosiliconized by twice ball milling, the time of twice ball milling is 1-8h, the rotation speed of ball milling is 400-800rpm, the ball milling medium is one or two of deionized water, ethanol, ethylene glycol, isopropyl alcohol, acetone, n-butanol; the ratio of zirconium oxide ball milling beads in the first ball milling process is (5-10mm):(2-4mm)=(2-5):1, the ball-to-material ratio is (10-5):1; the ratio of zirconium oxide ball milling beads in the second ball milling process is (5-10mm):(2-4mm):(0.4-1mm)=1:(2-5):(5-2), the ball-to-material ratio is (40-20):1.

[0009] Preferably, the ratio of nanosilicon powder in step (1) to lithium metal is: on the basis of stoichiometric ratio, lithium is 10wt% in excess, wherein the stoichiometric ratio includes Li 1.71 Si, Li 2.25 Si, Li 2.33 Si, Li 3.75 Si, Li 4.4 Si or more.

[0010] Preferably, the high-temperature melting in step (1) is to place the nanosilicon powder and lithium metal in a sealed container and melt in a high-temperature melting device, wherein the high-temperature melting device includes one or more of a box furnace, a tube furnace, and a muffle furnace; the sealed container includes one or more of an iron crucible, a quartz crucible, and a tantalum crucible.

[0011] Preferably, the coating process in step (2) is to coat the lithium-silicon alloy on the current collector by wet coating process or direct spraying process. The spraying equipment includes manual spraying equipment, semi-automatic spraying equipment, and fully automatic spraying equipment. The current collector material includes but is not limited to copper, nickel, titanium, and iron.

[0012] Preferably, the binder used in steps (2) and (3) includes one or more of PTFE, PIB, BR, NBR, SEBS, SBR, PVDF, PIB, SBS, SR, HNBR, PEVA, PMMA, and PAA, and the non-polar solvent used in the binder includes one or more of isopentane, n-pentane, cyclohexane, isooctane, cyclopentane, n-hexane, n-heptane, tetrahydrofuran, toluene, xylene, ethyl acetate, isobutyl isobutyrate, dichloromethane, and trichloromethane.

[0013] Preferably, the mass ratio of lithium-silicon alloy to binder in step (2) is (99-94):(1-6).

[0014] Preferably, the coating method in step (3) comprises one or more of a dry process, a wet process, and a spraying process; the dry process does not require drying; the wet process and the spraying process require a drying temperature of 80-120 DEG C and a drying time of 8-24 hours.

[0015] Preferably, the mass ratio of the silicon powder to the lithium-silicon alloy in step (3) is (50-90):(10-50).

[0016] The application also provides a sulfide full-solid-state battery comprising the double-layer structure nano-silicon-based negative electrode, an electrolyte film, and a dry cathode prepared by any of the above methods.

[0017] The cathode comprises one or more of NCM111, NCM424, NCM523, NCM622, or NCM811.

[0018] The electrolyte comprises one or more of Li2S-P2S5, Li7P3S 11 , Li6PS5Cl, Li 5.5 PS 4.5 Cl 1.5 , Li6PS5Br, Li6PS5I, Li 11 Si2PS 12 , Li 9.54 Si 1.74 P 1.44 S 11.7 Cl, Li 10 SnP2S 12 , or Li 10 GeP2S 12 .

[0019] The technical concept of the application is as follows:

[0020] The silicon negative electrode has a theoretical specific capacity of up to 3590 mAh g -1 at room temperature, and is a promising sulfide solid-state battery negative electrode material.

[0021] To solve the problems of pulverization and low capacity retention of pure silicon negative electrodes, lithium-silicon alloys with ion / electron conductivity advantages are prepared using nano-silicon and metal lithium as raw materials, and a silicon-based negative electrode with a double-layer structure is designed. +The disruption of the transport path indirectly enhances ion transport at the interface between the negative electrode and the electrolyte. Applying this bilayer structure to pouch cells based on sulfide electrolyte membranes makes it suitable for practical application and large-scale production.

[0022] Compared with the prior art, the beneficial effects of the technical solution of the present invention are as follows:

[0023] (1) This invention uses nano-silicon and metallic lithium as raw materials and obtains a lithium-silicon alloy by a high-temperature melting method, which has an electronic conductivity as high as 17.2 mS / cm. -1 It is much higher than the electronic conductivity of silicon (0.000611 mS / cm). -1 ).

[0024] (2) Compared to micron-sized silicon, the atoms on the surface of nano-sized silicon have a higher average binding energy, which allows for better stress release during the volume expansion of the silicon anode, effectively preventing structural collapse. Simultaneously, the nanostructure shortens the Li... + The diffusion distance is shorter, and Li has a faster diffusion rate along grain boundaries. + Diffusion pathway. However, commercially available nano-silicon is expensive. By using a simple ball milling process to nano-size silicon, the cost can be significantly reduced.

[0025] (3) Compared with pure silicon anodes, the double-layer structure nano-silicon-based anode has higher specific capacity and cycle stability in all-solid-state lithium-ion batteries. Attached Figure Description

[0026] Figure 1 The image shows the SEM characterization of the nanopowder obtained after ball milling in Example 1.

[0027] Figure 2 The Li prepared in Example 1 4.4 SEM characterization image of Si;

[0028] Figure 3 The ionic / electronic conductivity of the lithium-silicon alloy powder and silicon powder in Example 1;

[0029] Figure 4 XRD pattern of the bilayer structure nano-silicon-based anode provided in Example 1;

[0030] Figure 5 SEM characterization image of the bilayer structure nano-silicon-based anode provided in Example 1;

[0031] Figure 6 This is a schematic diagram of the principle of the battery prepared by the double-layer structure nano-silicon-based anode of the present invention;

[0032] Figure 7 This is a structural diagram of the soft-pack battery prepared by the double-layer structure nano-silicon-based anode of the present invention;

[0033] Figure 8 The circuit stability diagram is shown for the battery prepared from the bilayer structure nano-silicon-based anode of Example 1.

[0034] Figure 9 This is a comparison chart of the cycle stability of batteries prepared using the bilayer structure nano-silicon-based anodes of Examples 1-3;

[0035] Figure 10 This describes the application scenario of the soft-pack battery prepared by the double-layer structure nano-silicon-based anode of this invention. Detailed Implementation

[0036] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and not intended to limit it.

[0037] Example 1:

[0038] Weigh 2g of micron-sized silicon and place it in a zirconia ball mill jar. Use deionized water as the milling agent. First, mill with 18g of milling beads in a ratio of 5mm:2mm = 5:1 for 2 hours. Then, mill with 80g of milling beads in a ratio of 5mm:3mm:1mm = 1:5:2 for 2 hours. The total milling speed is 800 rpm. The milling beads are zirconia milling beads. Figure 1 As shown, the particle size of the powder after ball milling is in the hundreds of nanometers.

[0039] Nano-silicon powder and metallic lithium were weighed in a ratio of 1:4.4, with lithium in excess by 10 wt%. The mixture was then melted at 300 °C for 1 h to obtain Li. 4.4 Si. (As in...) Figure 2 As shown, the particles displayed by SEM are Li. 4.4 Si, with a particle size of approximately 5-10 μm. Additionally, please refer to... Figure 3 Li at room temperature 4.4 The ionic conductivity of Si is approximately 0.61 mS / cm. -1 The electronic conductivity is 17.20 mS / cm. -1 It is much higher than the ionic conductivity and electronic conductivity of nSi at room temperature.

[0040] Weigh out 400mg of silicon powder and Li in a ratio of 40:10. 4.4 Si 100mg, weigh out 42mgmL -1 Adhesive solutions PVDF / isobutyl isobutyrate 400μL and 100μL, first Li 4.4 Si is coated onto copper foil, dried at 80°C, and then silicon powder is coated onto Li. 4.4 A bilayer structure nano-silicon-based anode was obtained on the Si surface. For example... Figure 4 As shown, the diffraction peak at 40.98° is Li 4.4Si characteristic peak. As shown in Figure 5 SEM cross-section shows nSi and Li 4.4 Si is obviously layered.

[0041] Please refer to Figure 6 and Figure 7 The full battery of the double-layer structure nanometer silicon-based negative electrode | Li6PS5Cl | NCM811 is assembled, and compared with the full battery of the pure silicon negative electrode, the cycle performance is much better than that of the pure silicon negative electrode. Figure 8

[0042] Example two:

[0043] Take 2g of micron silicon and put it into a zirconium oxide ball mill jar. Use deionized water as the ball mill agent. First, use 18g of ball mill beads with a ratio of 5mm:2mm=5:1 to ball mill for 2h. Then use 80g of ball mill beads with a ratio of 5mm:3mm:1mm=1:5:2 to ball mill for 2h. The whole ball mill revolution speed is 800rpm, and the ball mill beads are zirconium oxide ball mill beads.

[0044] Take nanometer silicon powder and metal lithium according to the ratio of 1:4.4, with lithium excess of 10wt%, melt at 300℃ for 1h to get Li 4.4 Si.

[0045] Take silicon powder 600mg and Li 4.4 Si 100mg according to the ratio of 60:10, respectively take 42mg mL -1 binder solution PVDF / isobutyl isobutyrate 600μL and 100μL, first coat Li 4.4 Si on the copper foil, dry at 80℃, then coat the silicon powder on the surface of Li 4.4 Si to get the double-layer structure nanometer silicon-based negative electrode.

[0046] The full battery of the double-layer structure nanometer silicon-based negative electrode | Li6PS5Cl | NCM811 is assembled.

[0047] Example three:

[0048] Take 2g of micron silicon and put it into a zirconium oxide ball mill jar. Use deionized water as the ball mill agent. First, use 18g of ball mill beads with a ratio of 5mm:2mm=5:1 to ball mill for 2h. Then use 80g of ball mill beads with a ratio of 5mm:3mm:1mm=1:5:2 to ball mill for 2h. The whole ball mill revolution speed is 800rpm, and the ball mill beads are zirconium oxide ball mill beads.

[0049] Take nanometer silicon powder and metal lithium according to the ratio of 1:4.4, with lithium excess of 10wt%, melt at 300℃ for 1h to get Li 4.4 Si. ​

[0050] Silicon powder 200 mg and Li 4.4 Si 100 mg, 42 mg mL was weighed respectively -1 Binder solution PVDF / isobutyl isobutyrate 200 μL and 100 μL, Li 4.4 Si was coated on copper foil, and after drying at 80 °C, silicon powder was coated on Li 4.4 Si surface to obtain a double-layer structure nanosilicon-based negative electrode.

[0051] The double-layer structure nanosilicon-based negative electrode was assembled into a full cell with the structure of double-layer structure nanosilicon-based negative electrode | Li6PS5Cl | NCM811.

[0052] Figure 9 is a comparison chart of the cycle stability of the batteries prepared by the double-layer structure nanosilicon-based negative electrodes of Examples One to Three. The chart shows that nSi:Li 4.4 Si = 4:1 (mass ratio) is determined as the best ratio of the double-layer structure full active silicon-based negative electrode (nSi-Li 4.4 Si-DL4). The negative electrode structure at this ratio has the best rate performance and cycle performance. In Example Two, nSi:Li 4.4 Si = 6:1 (nSi-Li 4.4 Si-DL6), and in Example Three, nSi:Li 4.4 Si = 2:1 (nSi-Li 4.4 Si-DL2).

Claims

1. A method for preparing a bilayer structured nano-silicon-based anode, characterized in that, The method includes the following steps: (1) Prepare lithium-silicon alloy by melting nano-sized silicon powder and metallic lithium at a certain ratio at high temperature. The H2O and O2 content in the preparation process is required to be less than 1 ppm, the melting temperature is 200~350℃, and the melting time is 1~6 h. (2) The prepared lithium-silicon alloy is mixed with a binder and coated onto the current collector; (3) The nano-sized silicon powder is mixed with a binder and then coated onto the surface of the coated lithium silicon alloy to obtain a double-layer structured nano-silicon-based anode. In steps (1) and (3), the nano-sized silicon powder is obtained by two ball milling processes. The time for each ball milling process is 1 to 8 hours, the ball milling speed is 400 to 800 rpm, and the ball milling medium is one or two of deionized water, ethanol, ethylene glycol, isopropanol, acetone, and n-butanol. In the first ball milling process, the ratio of zirconia ball milling beads is (5 to 10 mm):(2 to 4 mm) = (2 to 5):1, and the ball-to-material ratio is (10 to 5):

1. In the second ball milling process, the ratio of zirconia ball milling beads is (5 to 10 mm):(2 to 4 mm):(0.4 to 1 mm) = 1:(2 to 5):(5 to 2), and the ball-to-material ratio is (40 to 20):

1.

2. The preparation method according to claim 1, characterized in that, In step (1), the ratio of nano-sized silicon powder to metallic lithium is as follows: based on the stoichiometric ratio, lithium is in excess by 10 wt%, where the stoichiometric ratio includes Li 1.71 Si, Li 2.25 Si, Li 2.33 Si, Li 3.75 Si, Li 4.4 One or more of Si.

3. The preparation method according to claim 1, characterized in that, In step (1), the high-temperature melting involves placing nano-sized silicon powder and metallic lithium in a sealed container and melting them in a high-temperature melting device. The high-temperature melting device used includes one or more of a box furnace, a tube furnace, and a muffle furnace. The sealed container includes one or more of an iron crucible, a quartz crucible, and a tantalum crucible.

4. The preparation method according to claim 1, characterized in that, The coating process in step (2) involves coating the lithium-silicon alloy onto the current collector using a wet coating process or a direct spraying process.

5. The preparation method according to claim 1, characterized in that, The binders used in steps (2) and (3) include one or more of PTFE, PIB, BR, NBR, SEBS, SBR, PVDF, PIB, SBS, SR, HNBR, PEVA, PMMA and PAA, and the non-polar solvents used in the binders include one or more of isopentane, n-pentane, cyclohexane, isooctane, cyclopentane, n-hexane, n-heptane, tetrahydrofuran, toluene, xylene, ethyl acetate, isobutyl isobutyrate, dichloromethane and trichloromethane.

6. The preparation method according to claim 1, characterized in that, In step (2), the mass ratio of lithium silicon alloy to binder is (99~94):(1~6).

7. The preparation method according to claim 1, characterized in that, The covering method in step (3) includes one or more of the following: dry process, wet process, and spraying process; the dry process does not require drying; the wet process and the spraying process require a drying temperature of 80~120℃ and a drying time of 8~24 h.

8. The preparation method according to claim 1, characterized in that, The mass ratio of silicon powder to lithium silicon alloy in step (3) is (50~90):(10~50).

9. A sulfide all-solid-state battery, characterized in that, Including the bilayer structured nano-silicon-based anode prepared by any one of claims 1-8.

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