Silicon-carbon negative electrode material and preparation method and application thereof

Abstract

The invention belongs to the field of batteries, and particularly discloses a silicon-carbon negative electrode material and a preparation method and application thereof. The silicon-carbon negative electrode material with a porous structure and containing the sulfide solid electrolyte is constructed, so that the contact interface between the negative electrode material and the sulfide electrolyte can be enlarged, the impedance is reduced, the ionic conductivity is improved, the lithium ion deposition is more uniform, and the safety, the cycle performance and the first effect of the solid lithium ion battery are improved.

Description

Technical Field

[0001] The present invention belongs to the field of batteries, and particularly relates to a silicon-carbon negative electrode material, a preparation method thereof, and an application thereof. Background Art

[0002] Solid-state lithium-ion batteries use highly intrinsically safe solid electrolyte materials to replace organic flammable liquid electrolytes, greatly improving the safety performance of the batteries. Among the currently studied solid electrolytes, sulfide solid electrolytes have good development prospects due to advantages such as high ionic conductivity, wide electrochemical window, wide operating temperature, low hardness, convenient processing, and the potential for flexibility. However, the interfacial contact between sulfide solid electrolytes and negative electrode materials is not ideal, with a large interfacial impedance, which hinders the transport of lithium ions between the negative electrode and the electrolyte, resulting in a decrease in the charge-discharge efficiency of the battery and affecting the performance of the battery. Especially during high-rate charge and discharge, this effect is more significant. At the same time, during the charge and discharge process of the battery, the negative electrode material will undergo volume expansion and contraction, and the rigid structure of the sulfide solid electrolyte is difficult to adapt to the volume change of the negative electrode material, resulting in a deterioration of the interfacial contact between the negative electrode and the electrolyte, and even interfacial separation, affecting the cycle performance of the battery. Moreover, during this process, the uneven deposition of lithium ions on the negative electrode side easily leads to the growth of lithium dendrites; the lithium dendrites will continuously grow and may penetrate the sulfide solid electrolyte, thereby triggering a short circuit inside the battery, seriously affecting the safety and cycle life of the battery. Summary of the Invention

[0003] Aiming at the problems involved in the above-mentioned prior art, the present invention will provide a silicon-carbon negative electrode material, a preparation method thereof, and an application thereof, and improve the defects in the safety and cycle performance of solid-state lithium-ion batteries by improving the negative electrode material.

[0004] To achieve the above object, the specific technical solutions include the following:

[0005] On the one hand, the present invention provides a preparation method of a silicon-carbon negative electrode material, including the following steps:

[0006] (1) Mix a lithium source, a phosphorus source, a sulfur source, and a halide uniformly to obtain a premix.

[0007] (2) Mix the premix and a pore-forming agent under stirring to obtain a mixture.

[0008] (3) Sinter the mixture in an inert gas atmosphere, and after ball milling, obtain a sulfide solid electrolyte.

[0009] (4) Ball-mill the sulfide solid electrolyte and the porous carbon material, heat it to a first temperature under the protection of an inert gas, and then introduce a gas containing silane to carry out a silicon deposition reaction; after adjusting the temperature to a second temperature, introduce a gas containing a carbon source to carry out a carbon deposition reaction to obtain a silicon-carbon negative electrode material.

[0010] In the method of the present invention, first, a pore-forming agent and raw materials of a sulfide solid electrolyte are sintered and ball-milled to obtain a porous sulfide solid electrolyte with a smaller particle size; then, nano-silicon is deposited inside the porous sulfide solid electrolyte and the porous carbon material by chemical vapor deposition, and then a uniform carbon coating layer is coated on the outside thereof to obtain a silicon-carbon negative electrode material. The silicon-carbon negative electrode material of the present invention includes a core and a carbon coating layer coated on the outer surface of the core. The core includes a porous sulfide solid electrolyte, porous carbon, and nano-silicon deposited in the pore structure of the core. Among them, in the silicon-carbon negative electrode material, the porous sulfide solid electrolyte and the porous carbon material provide a stable support structure, and their rich internal pore structure is conducive to the deposition of silicon inside to form nano-silicon; the nano-silicon provides a high capacity for the entire negative electrode material; the carbon coating layer on its surface serves as a passivation layer to protect silicon, which can effectively inhibit the volume expansion of silicon, improve the conductivity and ionic conductivity of the negative electrode material, and enhance the safety, cycle stability, and first efficiency of the battery.

[0011] Preferably, in step (1), the lithium source, phosphorus source, sulfur source, and halide are respectively based on the molar amounts of lithium element, phosphorus element, sulfur element, and halogen. The molar ratio of the lithium source, phosphorus source, sulfur source, and halide is n(Li):n(P):n(S):n(X)=(3-12):(1-3):(1-10):(1-3).

[0012] Preferably, in step (1), the lithium source includes at least one of Li2S, Li2S2, LiCl, LiBr, or LiI.

[0013] Preferably, in step (1), the phosphorus source includes at least one of P2S5, P4S9, or P4S 10 in the following.

[0014] Preferably, in step (1), the sulfur source includes at least one of P2S5, P4S9, or P4S 10 in the following.

[0015] Preferably, in step (1), the halide includes at least one of LiCl, LiBr, or LiI.

[0016] Preferably, in step (2), the pore-forming agent includes at least one of dimethyl silicone oil and diethyl silicone oil.

[0017] Preferably, in step (2), the mass ratio of the premix to the pore former is (0.2 - 3):(1 - 10); the temperature of the stirring is 10 - 40°C, the pressure of the stirring is 0.1 - 2.0 MPa, and the time of the stirring is 5 - 20 h.

[0018] In the present invention, the pore former and the premix are stirred and mixed under a certain pressure, which can make the raw materials more uniform and is conducive to the formation of a relatively uniform porous structure in the subsequent sulfide electrolyte.

[0019] Preferably, in step (3), the temperature of the sintering is 100 - 700°C, the time of the sintering is 1 - 10 h, the time of the ball milling is 1 - 5 h, and the rotation speed of the ball milling is 100 - 500 rpm.

[0020] The sulfide solid electrolyte is formed by sintering. At the same time, the high temperature during the sintering process enables the pore former to form pores in-situ, obtaining a large-particle porous sulfide solid electrolyte. After ball milling, the large-particle porous sulfide solid electrolyte is ground into small-particle porous sulfide solid electrolyte.

[0021] Preferably, in step (3), the inert gas includes at least one of nitrogen, argon, neon, or helium.

[0022] Preferably, in step (4), the time of the ball milling is 1 - 5 h, and the rotation speed of the ball milling is 100 - 500 rpm.

[0023] The sulfide solid electrolyte and the porous carbon material can be mixed more uniformly by ball milling.

[0024] Preferably, in step (4), the mass ratio of the sulfide solid electrolyte to the porous carbon material is (2 - 3):(7 - 8). The porous carbon has good electrical conductivity. A higher proportion of the porous carbon can increase the electron transport ability of the silicon-carbon anode material and improve the rate performance of the battery; at the same time, the pore structure of the porous carbon is more stable than that of the porous sulfide. A higher proportion of the porous carbon in the silicon-carbon anode material can improve the cycling performance of the material. At the same time, the inventors of the present invention have found through research that under the above mass ratio range of the two, the battery has better initial efficiency and cycling performance.

[0025] Preferably, in step (4), the first temperature is 500 - 600°C, the time of the silicon deposition reaction is 1.5 - 6 h, the flow rate of the silane-containing gas is 1 - 5 L / min, the silane-containing gas includes silane and an inert gas, and the silane includes at least one of monosilane, disilane, trisilane, or tetrasilane.

[0026] Under the flow rate, deposition reaction temperature and time of a suitable gaseous silicon source, it is conducive to the deposition of nano-silicon inside the sulfide electrolyte and the porous carbon material, which can significantly improve the material capacity.

[0027] Preferably, in step (4), in the gas containing a carbon source, the carbon source includes hydrocarbons.

[0028] More preferably, the hydrocarbon includes at least one of acetylene, methane, propane, propylene or cyclohexane.

[0029] Preferably, in step (4), the second temperature is 600 - 650 °C, the time for the carbon deposition reaction is 180 min - 300 min, the flow rate of the gas containing a carbon source is 2 - 5 L / min, and the gas containing a carbon source includes acetylene and an inert gas.

[0030] Preferably, in step (4), the second temperature is 600 - 650 °C, and the time for the carbon deposition reaction is 200 min - 280 min.

[0031] After depositing nano-silicon inside the sulfide electrolyte and the porous carbon material, depositing a carbon coating layer on the surface can protect the nano-silicon. Under the flow rate, deposition reaction temperature and time of a suitable gaseous carbon source, it is conducive to coating a more uniform carbon layer on the outer surface.

[0032] Preferably, in step (4), after heating to the first temperature, it further includes a heat preservation process of 15 - 60 min.

[0033] Preferably, in step (4), after adjusting the temperature to the second temperature, it further includes a heat preservation process of 15 - 60 min.

[0034] Before depositing silicon and carbon, heat preservation at the target temperature can achieve preheating in advance, improving the efficiency and quality of depositing silicon or carbon.

[0035] On the other hand, the present invention provides a silicon-carbon negative electrode material prepared by the preparation method of the silicon-carbon negative electrode material described above.

[0036] Preferably, the silicon-carbon negative electrode material includes a core and a carbon coating layer coated on the outer surface of the core. The core includes a porous sulfide solid electrolyte, porous carbon, and nano-silicon deposited in the pore structure of the core.

[0037] In addition, the present invention also provides a solid-state lithium-ion battery, including a positive electrode sheet, a negative electrode sheet, and a sulfide electrolyte. The negative electrode sheet includes the silicon-carbon negative electrode material described above.

[0038] Preferably, the positive electrode plate further includes a positive electrode active material, which includes at least one of lithium sulfide, lithium cobalt oxide (LiCoO2), lithium manganese oxide (LiMn2O4), lithium iron phosphate (LiFePO4), lithium nickel cobalt manganese oxide (Li(NiCoMn)O2), and (Li(NiCoAl)O2).

[0039] Preferably, the positive electrode plate further includes a conductive agent, which includes at least one of conductive carbon black (such as Li435), conductive graphite, carbon nanotube conductive paste (CNT), and graphene.

[0040] Preferably, the binder for the positive electrode plate is at least one of polyvinylidene fluoride (PVDF), polyacrylonitrile (PAN), and polyimide (PI).

[0041] Preferably, the negative electrode plate includes a conductive agent, which includes Super P (S-P).

[0042] The solid-state lithium-ion battery is prepared by a conventional method in the art. For example, the method includes the following steps:

[0043] (1) Mix the positive electrode active material, conductive agent, binder, and solvent evenly to obtain a positive electrode slurry; coat the positive electrode slurry on a current collector, and then perform drying, rolling, and sheet making to obtain a positive electrode plate.

[0044] (2) Mix the silicon-carbon negative electrode material, sulfide electrolyte, and conductive agent evenly, and cold press them into a double-layer sheet structure of a negative electrode plate and an electrolyte sheet. Then, attach the positive electrode plate to the other side of the electrolyte sheet to obtain an electrode with a three-layer sheet structure including a positive electrode plate, an electrolyte sheet, and a negative electrode plate in sequence. Finally, place current collectors on both sides to obtain a solid-state lithium-ion battery.

[0045] Preferably, the solvent includes N-methylpyrrolidone. In the positive electrode slurry, the mass percentage content of the positive electrode active material is 88% - 95%, the mass percentage content of the conductive agent is 2% - 10%, and the mass percentage content of the binder is 3% - 7%.

[0046] Compared with the prior art, the present invention has the following beneficial effects: The present invention constructs a silicon-carbon negative electrode material with a porous structure and containing a sulfide solid electrolyte, which can increase the contact interface between the negative electrode material and the sulfide electrolyte, reduce the impedance, improve the ionic conductivity, make the lithium-ion deposition more uniform, and improve the safety, cycle performance, and initial efficiency of the solid-state lithium-ion battery. Description of the Drawings

[0047] Figure 1This is a schematic structural diagram of the silicon-carbon anode material of the present invention. The silicon-carbon anode material includes a core and a carbon coating layer covering the outer surface of the core. The core includes a porous sulfide solid electrolyte, porous carbon, and nano-silicon deposited in the pore structure of the core. Detailed implementation manners

[0048] To better illustrate the purpose, technical solution, and advantages of the present invention, the present invention will be further described below through specific examples. The test methods used in the examples and / or comparative examples are all conventional methods unless otherwise specified; the materials, reagents, etc. used are all commercially available unless otherwise specified.

[0049] The porous carbon material used in the following examples and comparative examples is a commercially purchased porous carbon material. Among them, the proportion of micropores and mesopores (2 nm to 50 nm) in the porous carbon material is 80% to 90%, and the porosity is 50% to 90%.

[0050] Example 1

[0051] A preparation method of a silicon-carbon anode material includes the following steps:

[0052] (1) In a glove box, take Li2S, P2S5, and LiCl at a molar ratio of 4:1:2 and mix them evenly to obtain a premix;

[0053] (2) According to a mass ratio of 1:10, put the premix and dimethyl silicone oil into a stirring kettle, set the stirring temperature to 26 °C, the stirring pressure to 1.0 MPa, and stir for 10 h to obtain a mixture;

[0054] (3) Place the mixture in a rotary furnace and sinter it at 340 °C for 7 h in a nitrogen atmosphere to obtain large-particle porous sulfide solid electrolyte (Li6PS5Cl); add the large-particle porous sulfide solid electrolyte to a ball mill and ball mill it at a rotation speed of 350 rpm for 3 h to obtain porous sulfide solid electrolyte powder;

[0055] (4) According to a mass ratio of 2:8, put the porous sulfide solid electrolyte powder and the porous carbon material into a ball mill and ball mill them at a rotation speed of 350 rpm for 3 h to mix evenly;

[0056] (5) Then put the uniformly mixed materials into a fluidized bed, first introduce nitrogen for protection at a flow rate of 15 L / min, then heat from room temperature to 520 °C and keep it for 20 min; at this temperature, introduce silane gas with a silane flow rate of 2 L / min, and keep it for 330 min to carry out the silicon deposition reaction, then turn off the silane gas; continue to heat from this temperature to 600 °C and keep it for 20 min, then at this temperature, introduce acetylene with a flow rate of 3 L / min, and keep it for 200 min to carry out carbon deposition coating. After the coating is completed and the equipment cools down, take out the materials to obtain the silicon-carbon anode material.

[0057] Example 2

[0058] The difference between this example and Example 1 is that in step (4), the mass ratio of the porous sulfide solid electrolyte powder to the porous carbon material is 3:7, and the rest is the same.

[0059] Example 3

[0060] The difference between this example and Example 1 is that in step (5), acetylene with a flow rate of 3 L / min is introduced and kept for 280 min to carry out carbon deposition coating to increase the thickness of the coating layer, and the rest is the same.

[0061] Example 4

[0062] The difference between this example and Example 1 is that in step (4), the mass ratio of the porous sulfide solid electrolyte powder to the porous carbon material is 3:7, and in step (5), acetylene with a flow rate of 3 L / min is introduced and kept for 280 min to carry out carbon deposition coating, and the rest is the same.

[0063] Comparative Example 1

[0064] The difference between this comparative example and Example 1 is that in step (4), the mass ratio of the porous sulfide solid electrolyte powder to the porous carbon material is 1:9, and the rest is the same.

[0065] Comparative Example 2

[0066] The difference between this comparative example and Example 1 is that in step (4), the mass ratio of the porous sulfide solid electrolyte powder to the porous carbon material is 4:6, and the rest is the same.

[0067] Comparative Example 3

[0068] The difference between this comparative example and Example 1 is that acetylene with a flow rate of 3 L / min is introduced and kept for 120 min to carry out carbon deposition coating, and the rest is the same.

[0069] Comparative Example 4

[0070] The difference between this comparative example and Example 1 is that in step (4), the mass ratio of the porous sulfide solid electrolyte powder to the porous carbon material is 9:1, and the rest is the same.

[0071] Comparative Example 5

[0072] The difference between this comparative example and Example 1 is that this comparative example does not perform steps (1) to (3), and uses commercially available non-porous Li6PS5Cl and porous carbon material to carry out the process of step (4), and the rest is the same.

[0073] Comparative Example 6

[0074] The difference between this comparative example and Example 1 is that this comparative example does not add the sulfide solid electrolyte, that is, this comparative example does not perform steps (1) to (3), and uses an equal mass of porous carbon material to make up for the lack of the porous sulfide solid electrolyte powder.

[0075] A method for preparing a solid-state lithium-ion battery includes the following steps:

[0076] (1) Mix Li2MnO3 and layered LiCoO2 evenly at a mass ratio of 6:4 to obtain a lithium-rich manganese-based cathode material; mix the cathode material, carbon nanotubes (CNT), carbon black (Li435), polyvinylidene fluoride (PVDF) and N-methylpyrrolidone (NMP) evenly according to solid contents of 97.3 wt.%, 0.5 wt.%, 1 wt.%, 1.2 wt.% respectively to make a cathode slurry; coat the slurry evenly on an aluminum foil according to a certain surface density, and obtain a cathode sheet through drying, rolling and sheet making;

[0077] (2) Weigh the anode material (corresponding to the above-mentioned examples and comparative examples respectively), Li6PS5Cl (commercially available), CMC and Super P (S-P) according to a mass ratio of 45:45:5:5, manually mix them evenly in a mortar for 30 min, and cold press the above-mentioned composite anode material and the electrolyte layer (Li6PS5Cl) in sequence under a pressure of 300 MPa to obtain a double-layer sheet structure, and the pressure holding time is 3 min; then stick the cathode sheet obtained in step (1) on the other side of the electrolyte sheet, and obtain a three-layer sheet structure under a pressure of 200 Mpa, and keep the pressure for 1 min. Finally, place two stainless steel rods on both sides as current collectors to obtain a all-solid-state battery; the battery is cycled 300 times at a current density of 0.1C, and the initial efficiency of the battery and the retention rate of the capacity after 300 cycles are tested.

[0078] Table 1 Initial efficiency of the battery and retention rate of the capacity after 300 cycles

[0079]

[0080]

[0081] As can be seen from Example 1 and Comparative Examples 5-6, adding a porous sulfide solid electrolyte to the silicon-carbon anode material to construct a silicon-carbon anode material with a porous structure and containing a sulfide solid electrolyte can increase the contact interface between the anode material and the sulfide electrolyte, improve the structural stability of the material, reduce the impedance, enhance the ionic conductivity, make the lithium-ion deposition more uniform, and improve the safety, cycle performance, and initial efficiency of the solid-state lithium-ion battery. In addition, the silicon and carbon anode materials of the present invention are deposited by chemical vapor deposition (CVD), and it is selected to deposit silicon first and then carbon coating. On the one hand, in the way of carbon coating silicon, during the charge and discharge process of the battery, the volume expansion of silicon is relatively large. The carbon coating layer can not only increase the conductivity of the material but also effectively inhibit the volume expansion of silicon, further improving the stability and safety of the battery. On the other hand, depositing silicon first and then carbon coating can also avoid depositing silicon and carbon coating simultaneously, which cannot ensure that the deposited nano-silicon is completely coated by the carbon layer. And due to the high chemical activity of silicon, when the incompletely coated material is exposed to air, silicon will react with oxygen to release a large amount of heat and is prone to spontaneous combustion. Moreover, the volume expansion and contraction of silicon are not restricted by the carbon coating layer and will gradually powderize and fall off during the cycle, and the cycle performance of the battery will rapidly decrease.

[0082] In Comparative Example 1, Example 1, Example 2, Comparative Example 2, and Comparative Example 4, the mass ratios of the porous sulfide solid electrolyte powder to the porous carbon material are 1:9, 2:8, 3:7, 4:6, and 9:1 respectively. As the porous sulfide solid electrolyte powder increases and the porous carbon material decreases, the initial efficiency and cycle performance first increase and then decrease. It can be seen that when the mass ratio of the porous sulfide solid electrolyte powder to the porous carbon material is (2-3):(7-8), the initial efficiency and cycle performance are relatively good.

[0083] In Comparative Example 3, Example 1, and Example 3, the carbon deposition and coating times are 120 min, 200 min, and 280 min respectively. As the carbon deposition and coating time increases, the thickness of the carbon coating layer increases, and the initial efficiency and cycle performance first increase and then decrease. It can be seen that increasing the carbon coating layer to a certain extent can improve the electrochemical performance of the silicon-carbon anode material. Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit the protection scope of the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A preparation method of a silicon-carbon negative electrode material, characterized in that It includes the following steps: (1) Mix a lithium source, a phosphorus source, a sulfur source, and a halide uniformly to obtain a premix. (2) Mix the premix and a pore former under stirring to obtain a mixture. (3) Sinter the mixture in an inert gas atmosphere, and after ball milling, obtain a sulfide solid electrolyte. (4) Ball mill the sulfide solid electrolyte and a porous carbon material, heat it to a first temperature under inert gas protection, and then introduce a gas containing silane to carry out a silicon deposition reaction; then adjust the temperature to a second temperature, and introduce a gas containing a carbon source to carry out a carbon deposition reaction to obtain a silicon-carbon negative electrode material.

2. As described in claim 1, characterized in that, In step (4), the mass ratio of the sulfide solid electrolyte to the porous carbon material is (2 - 3):(7 - 8).

3. The preparation method of the silicon-carbon negative electrode material according to claim 1, characterized in that It includes at least one of the following: In step (1), taking the lithium source, phosphorus source, sulfur source, and halide in terms of the molar amounts of lithium element, phosphorus element, sulfur element, and halogen respectively, the molar ratio of the lithium source, phosphorus source, sulfur source, and halide n(Li):n(P):n(S):n(X) = (3 - 12):(1 - 3):(1 - 10):(1 - 3); In step (1), the lithium source includes at least one of Li2S, Li2S2, LiCl, LiBr, or LiI. In step (1), the phosphorus source includes at least one of P2S5, P4S9 or P4S 10 ; In step (1), the sulfur source includes at least one of P2S5, P4S9 or P4S 10 ; In step (1), the halide includes at least one of LiCl, LiBr, or LiI. In step (2), the pore former includes at least one of dimethyl silicone oil and diethyl silicone oil. In step (4), in the gas containing a carbon source, the carbon source includes a hydrocarbon.

4. The preparation method of the silicon-carbon anode material according to claim 1, wherein, In step (2), the mass ratio of the premix to the pore former is (0.2 - 3):(1 - 10); the temperature of the stirring is 10 - 40 °C, the pressure of the stirring is 0.1 - 2.0 MPa, and the time of the stirring is 5 - 20 h.

5. The preparation method of the silicon-carbon anode material according to claim 1, wherein In step (3), the temperature of the sintering is 100 - 700 °C, the time of the sintering is 1 - 10 h, the time of the ball milling is 1 - 5 h, and the rotation speed of the ball milling is 100 - 500 rpm.

6. The preparation method of the silicon-carbon anode material according to claim 1, characterized in that, It includes at least one of the following: In step (4), the time of the ball milling is 1 - 5 h, and the rotation speed of the ball milling is 100 - 500 rpm; In step (4), after heating to the first temperature, it further includes a heat preservation process of 15 - 60 min; In step (4), after adjusting the temperature to the second temperature, it further includes a heat preservation process of 15 - 60 min.

7. The preparation method of the silicon-carbon anode material according to claim 1, characterized in that In step (4), the first temperature is 500 - 600 °C, the time of the silicon deposition reaction is 1.5 - 6 h, the flow rate of the gas containing silane is 1 - 5 L / min, the gas containing silane includes silane and an inert gas, and the silane includes at least one of monosilane, disilane, trisilane, and tetrasilane.

8. The preparation method of the silicon-carbon negative electrode material according to claim 1, characterized in that, In step (4), the second temperature is 600 - 650 °C, the time of the carbon deposition reaction is 180 min - 300 min, the flow rate of the gas containing a carbon source is 2 - 5 L / min, and the gas containing a carbon source includes acetylene and an inert gas.

9. A silicon-carbon negative electrode material prepared by the preparation method of the silicon-carbon negative electrode material as claimed in claims 1 - 8.

10. A solid-state lithium-ion battery, characterized in that, It includes a positive electrode plate, a negative electrode plate and a sulfide electrolyte, and the negative electrode includes the silicon-carbon negative electrode material described in claim 9.

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