Solid electrolyte coated silicon carbon negative electrode material and preparation method thereof, all-solid-state battery and electric device

Abstract

The invention relates to a solid electrolyte coated silicon-carbon negative electrode material and a preparation method thereof, an all-solid-state battery and an electric device, and belongs to the technical field of methods or devices for directly converting chemical energy into electric energy. The solid electrolyte coated silicon-carbon negative electrode material comprises a silicon-carbon negative electrode material and a solid electrolyte coating layer arranged on the surface of the silicon-carbon negative electrode material, the solid electrolyte coating layer comprises at least one of sulfide electrolyte and halide electrolyte; the silicon-carbon negative electrode material comprises an inner core and a carbon coating layer arranged on the surface of the inner core, the inner core comprises a porous carbon matrix and a silicon-based material positioned in pores of the porous carbon matrix. The solid-state electrolyte coated silicon-carbon negative electrode material enables an all-solid-state battery to have high ionic conductivity and first efficiency and excellent cycling stability.

Description

Technical Field

[0001] The present invention relates to the technical field of methods or devices for directly converting chemical energy into electrical energy, and in particular to a solid electrolyte-coated silicon-carbon negative electrode material and a preparation method thereof, an all-solid-state battery, and an electrical device. Background Art

[0002] Compared to liquid lithium-ion batteries, all-solid-state batteries have obvious advantages in key performances such as safety, energy density and cycle life, especially all-solid-state batteries using sulfide solid electrolytes and halide solid electrolytes, which have high ionic conductivity, good mechanical properties and a wide operating temperature range. However, the contact between the solid electrolyte and the negative electrode is poor, and there is a large interface impedance, which hinders the transmission of lithium ions, resulting in a low charge and discharge efficiency of the battery. At the same time, during the charge and discharge process of the battery, the negative electrode material (such as silicon carbon) will undergo volume expansion and contraction, and the rigid solid electrolyte is difficult to adapt to the volume change of the negative electrode material, resulting in further deterioration of the contact between the solid electrolyte and the negative electrode, and even interface separation, which has a serious impact on the cycle performance of the battery. In addition, during the charge and discharge process of the battery, the uneven deposition of lithium ions on the negative electrode side is easy to lead to the generation of lithium dendrites, which can continuously grow and may penetrate the solid electrolyte, thereby causing a short circuit inside the battery, seriously affecting the safety and cycle life of the battery. Summary of the Invention

[0003] The purpose of the present invention is to overcome the shortcomings of the prior art and provide a solid electrolyte coated silicon carbon negative electrode material and its preparation method, an all-solid-state battery, and an electrical device.

[0004] To achieve the above object, the technical solution adopted by the present invention is:

[0005] In a first aspect, the present invention provides a solid electrolyte-coated silicon-carbon negative electrode material, comprising a silicon-carbon negative electrode material and a solid electrolyte coating layer provided on the surface of the silicon-carbon negative electrode material;

[0006] The solid electrolyte coating layer includes at least one of a sulfide electrolyte and a halide electrolyte;

[0007] The silicon-carbon negative electrode material comprises a core and a carbon coating layer arranged on the surface of the core; the core comprises a porous carbon matrix and a silicon-based material located in the pores of the porous carbon matrix.

[0008] The solid electrolyte coated silicon-carbon negative electrode material of the present invention is mainly composed of a porous carbon matrix, a silicon-based material, a carbon coating layer and a solid electrolyte coating layer, wherein the porous carbon matrix serves as a carrier of the silicon-based material, providing a stable support structure, and the silicon-based material located in the pores of the porous carbon matrix provides high capacity for the entire negative electrode material. The carbon coating layer can not only serve as a passivation layer for the silicon-based material to effectively inhibit the reaction between it and the electrolyte, but also inhibit the volume expansion of the silicon-based material, and at the same time is beneficial to improving the conductivity of the negative electrode material; and the solid electrolyte coating layer arranged on the surface of the carbon coating layer has a more critical role. It can not only enhance the structural stability and mechanical properties of the negative electrode material, but also significantly improve the interface contact performance between the negative electrode material and the solid electrolyte sheet, thereby reducing the interface impedance and improving the ionic conductivity, thereby improving the cycle stability and first effect of the all-solid-state battery.

[0009] The present invention has no particular limitation on the silicon-carbon negative electrode material, as long as it can achieve the purpose of the present invention. For example, the specific surface area of ​​the porous carbon matrix in the silicon-carbon negative electrode material is 1400-1800 m 2 / g, pore volume is 0.5~1.5cm 3 / g, pore size distribution micropores (≤2nm) ≥80%; silicon-based materials include but are not limited to elemental silicon, silicon oxide, etc., preferably nano-silicon.

[0010] As a preferred embodiment of the solid electrolyte coated silicon carbon negative electrode material of the present invention, the sulfide electrolyte includes Li6PS5X, Li 10 GeP2S 12 、Li7P3S 11 、Li 9.54 Si 1.74 P 1.44 S 11.7 C l0.3 、Li 6.6 Si 0.6 Sb 0.4 At least one of S5I; X in the Li6PS5X is selected from any one of Cl, Br, and I.

[0011] As a preferred embodiment of the solid electrolyte-coated silicon-carbon negative electrode material of the present invention, the halide electrolyte includes at least one of Li2ZrCl6, Li2HfCl6, Li3YCl6, LiTaCl6, LiNbCl6, LiTaOCl4, and LiNbOCl4.

[0012] As a preferred embodiment of the solid electrolyte-coated silicon-carbon negative electrode material of the present invention, the average particle size of the core is 4 to 8 μm; optionally, the average particle size of the core can be specifically any one of 4 μm, 4.5 μm, 5 μm, 5.5 μm, 6 μm, 6.5 μm, 7 μm, 7.5 μm, 8 μm or any two of the range values.

[0013] As a preferred embodiment of the solid electrolyte-coated silicon-carbon negative electrode material of the present invention, the average thickness of the carbon coating layer is 50 to 300 nm; optionally, the average thickness of the carbon coating layer can be any one or any two of 50 nm, 100 nm, 150 nm, 200 nm, 250 nm, and 300 nm.

[0014] As a preferred embodiment of the solid electrolyte coated silicon-carbon negative electrode material of the present invention, the average thickness of the solid electrolyte coating layer is 50 to 500 nm; alternatively, the average thickness of the solid electrolyte coating layer can be specifically 50 nm, 80 nm, 100 nm, 120 nm, 150 nm, 180 nm, 200 nm, 220 nm, 250 nm, 280 nm, 300 nm, 320 nm, 350 nm, 380 nm, 400 nm, 420 nm, 450 nm, 480 nm, 500 nm, or any two of the range values. By regulating the average thickness of the solid electrolyte coating layer within the above range, not only can sufficient ion conduction channels be ensured, the internal resistance of the battery is reduced, and the charge and discharge efficiency of the battery is improved, but also a stable interface is formed between the electrode and the electrolyte, reducing interface side reactions and improving battery cycle performance.

[0015] The average thickness of the carbon coating layer in the solid electrolyte coated silicon-carbon negative electrode material and the average thickness of the solid electrolyte coating layer can be tested by conventional methods in the field. For example, the solid electrolyte coated silicon-carbon negative electrode material is sliced ​​using a focused ion beam (FIB), and then characterized by a high-resolution transmission electron microscope (HRTEM). Within the same selected area, five positions of the carbon coating layer or the solid electrolyte coating layer are randomly selected to measure the thickness of the carbon coating layer and the thickness of the solid electrolyte coating layer. The arithmetic average of the thickness of the carbon coating layer at the five different positions is calculated to obtain the average thickness of the carbon coating layer; the arithmetic average of the thickness of the solid electrolyte coating layer at the five different positions is calculated to obtain the average thickness of the solid electrolyte coating layer.

[0016] In a second aspect, the present invention provides a method for preparing the above-mentioned solid electrolyte-coated silicon-carbon negative electrode material, comprising the following steps:

[0017] The silicon-carbon negative electrode material and the solid electrolyte are mixed and then ball-milled to obtain a solid electrolyte-coated silicon-carbon negative electrode material;

[0018] The solid electrolyte includes at least one of a sulfide electrolyte and a halide electrolyte;

[0019] The silicon-carbon negative electrode material comprises a core and a carbon coating layer arranged on the surface of the core; the core comprises a porous carbon matrix and a silicon-based material located in the pores of the porous carbon matrix.

[0020] The present invention imposes no particular limitations on the ball milling process in the above-mentioned preparation method, as long as the objectives of the present invention can be achieved. For example, a planetary ball mill can be used for the ball milling process, using zirconia grinding balls with a diameter of 1 to 6 mm; the mass ratio of the grinding balls to the raw materials (i.e., the silicon-carbon negative electrode material and the solid electrolyte mixture) is (10 to 20):1 (for example, 10:1, 11:1, 12:1, 13:1, 14:1, 15:1, 16:1, 17:1, 18:1, 19:1, 20:1, etc.); and the entire ball milling process is carried out in an inert atmosphere (e.g., argon or nitrogen) to prevent the solid electrolyte from reacting with oxygen or moisture.

[0021] As a preferred embodiment of the preparation method of the solid electrolyte-coated silicon-carbon negative electrode material of the present invention, the mass ratio of the silicon-carbon negative electrode material to the solid electrolyte is (2-20):1, preferably (2-15):1, and specifically can be any one or any two of 2:1, 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, 9:1, 10:1, 13:1, 15:1, 18:1, and 20:1. By regulating the mass ratio of the silicon-carbon negative electrode material to the solid electrolyte within the above range, the solid electrolyte can better form a solid electrolyte coating layer of appropriate thickness on the surface of the silicon-carbon negative electrode material.

[0022] As a preferred embodiment of the preparation method of the solid electrolyte coated silicon-carbon negative electrode material of the present invention, the ball milling speed is 200-500 rpm and the time is 1-5 hours. Optionally, the ball milling speed can be any one of 200 rpm, 250 rpm, 300 rpm, 350 rpm, 400 rpm, 450 rpm, 500 rpm or any two of the range values; the ball milling time is any one of 1 hour, 1.5 hours, 2 hours, 2.5 hours, 3 hours, 3.5 hours, 4 hours, 4.5 hours or any two of the range values. By regulating the ball milling speed and time within the above range, a more uniform solid electrolyte coating layer can be obtained.

[0023] As a preferred embodiment of the method for preparing the solid electrolyte-coated silicon-carbon negative electrode material of the present invention, the average particle size of the sulfide electrolyte is 1 to 3 μm; and / or the average particle size of the halide electrolyte is 500 nm to 2 μm. For example, the average particle size of the sulfide electrolyte can be any one of 1 μm, 1.3 μm, 1.5 μm, 1.8 μm, 2 μm, 2.2 μm, 2.5 μm, 2.7 μm, 3 μm, or any two of the range values; the average particle size of the halide electrolyte is any one of 500 nm, 800 nm, 1 μm, 1.2 μm, 1.4 μm, 1.6 μm, 1.8 μm, or 2 μm, or any two of the range values.

[0024] In a third aspect, the present invention provides an all-solid-state battery comprising the above-mentioned solid electrolyte-coated silicon-carbon negative electrode material.

[0025] In a fourth aspect, the present invention provides an electrical device comprising the above-mentioned all-solid-state battery, wherein the all-solid-state battery serves as a power supply for the electrical device.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] The solid electrolyte coated silicon-carbon negative electrode material of the present invention is mainly composed of a porous carbon matrix, a silicon-based material, a carbon coating layer and a solid electrolyte coating layer, wherein the porous carbon matrix serves as a carrier of the silicon-based material, providing a stable support structure, and the silicon-based material located in the pores of the porous carbon matrix provides high capacity for the entire negative electrode material. The carbon coating layer can not only serve as a passivation layer for the silicon-based material to effectively inhibit the reaction between it and the electrolyte, but also inhibit the volume expansion of the silicon-based material, and at the same time is beneficial to improving the conductivity of the negative electrode material; and the solid electrolyte coating layer arranged on the surface of the carbon coating layer has a more critical role. It can not only enhance the structural stability and mechanical properties of the negative electrode material, but also significantly improve the interface contact performance between the negative electrode material and the solid electrolyte sheet, thereby reducing the interface impedance and improving the ionic conductivity, thereby improving the cycle stability and first effect of the all-solid-state battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is a schematic diagram of the structure of the solid electrolyte coated silicon-carbon negative electrode material of the present invention. DETAILED DESCRIPTION

[0029] In order to better illustrate the purpose, technical solutions and advantages of the present invention, the present invention will be further described below in conjunction with specific embodiments.

[0030] Unless otherwise specified, other materials and reagents used in the examples can be obtained from commercial sources.

[0031] Example 1

[0032] This embodiment provides a solid electrolyte coated silicon carbon negative electrode material (such as Figure 1 As shown), the preparation method includes the following steps: in a glove box, a silicon-carbon negative electrode material and a solid electrolyte (Li2ZrCl4F2) are mixed in a mass ratio of 6:1, placed in a ball mill, and ball-milled at a speed of 300 rpm for 2 hours to obtain a solid electrolyte-coated silicon-carbon negative electrode material; wherein the entire ball milling process is carried out in a high-purity argon (99.999%) environment, and the mass ratio of the grinding balls (composed of zirconium oxide) to the raw materials (silicon-carbon negative electrode material and solid electrolyte) is 20:1.

[0033] The above silicon-carbon negative electrode material is prepared by the following method:

[0034] 1000g of porous carbon material (specific surface area of ​​1600m 2 / g, pore volume is 1cm 3 / g, pore size distribution of micropores 1-2nm accounting for ≥80%) was placed on the fluidized bed substrate, and nitrogen was first introduced at a flow rate of 15L / min to protect the temperature to 520°C and keep it warm for 20 minutes; then silane gas was introduced with a silane flow rate of 2L / min, and the temperature was kept warm for 330 minutes; then the silane gas was turned off and the temperature was continued to be raised to 600°C and kept warm for 20 minutes, and then acetylene was introduced at a flow rate of 3L / min and kept warm for 200 minutes to obtain a silicon-carbon negative electrode material.

[0035] Example 2

[0036] This embodiment provides a solid electrolyte-coated silicon-carbon negative electrode material, and its preparation method is different from that of Example 1 only in that the solid electrolyte is Li6PS5Cl.

[0037] Example 3

[0038] This embodiment provides a solid electrolyte-coated silicon-carbon negative electrode material, and its preparation method is different from that of Example 1 only in that the solid electrolyte is Li2ZrCl6.

[0039] Example 4

[0040] This embodiment provides a solid electrolyte coated silicon carbon negative electrode material, and its preparation method is different from that of embodiment 1 only in that the solid electrolyte is Li 10 GeP2S 12 .

[0041] Example 5

[0042] This embodiment provides a solid electrolyte-coated silicon-carbon negative electrode material. The preparation method thereof is different from that of Example 1 only in that the mass ratio of the silicon-carbon negative electrode material to the solid electrolyte is 2:1.

[0043] Example 6

[0044] This embodiment provides a solid electrolyte-coated silicon-carbon negative electrode material. The preparation method thereof is different from that of Example 1 only in that the mass ratio of the silicon-carbon negative electrode material to the solid electrolyte is 10:1.

[0045] Example 7

[0046] This embodiment provides a solid electrolyte-coated silicon-carbon negative electrode material. The preparation method thereof is different from that of Example 1 only in that the mass ratio of the silicon-carbon negative electrode material to the solid electrolyte is 15:1.

[0047] Comparative Example 1

[0048] This comparative example provides a carbon-coated silicon-carbon negative electrode material, the preparation method of which comprises the following steps:

[0049] 1000g of porous carbon material (the same as in Example 1) was placed on the base of a fluidized bed, and nitrogen was introduced at a flow rate of 15L / min to protect the temperature and raise it to 520°C and keep it warm for 20min; then silane gas was introduced with a silane flow rate of 2L / min, and the temperature was kept warm for 330min; then the silane gas was turned off and the temperature was continued to rise to 600°C and kept warm for 20min, and then acetylene was introduced at a flow rate of 3L / min and continued to be kept warm for 200min to obtain a carbon-coated silicon-carbon negative electrode material.

[0050] Comparative Example 2

[0051] This comparative example provides a solid electrolyte coated silicon-carbon negative electrode material, the preparation method of which differs from that of Example 1 only in that the silicon-carbon negative electrode material is different (without a carbon coating layer);

[0052] The above silicon-carbon negative electrode material is prepared by the following method:

[0053] 1000 g of porous carbon material (the same as in Example 1) was placed on the base of the fluidized bed, and nitrogen was introduced at a flow rate of 15 L / min to protect the temperature to 520°C and keep warm for 20 minutes; then silane gas was introduced with a silane flow rate of 2 L / min, and the temperature was kept warm for 330 minutes; then the silane gas was turned off and allowed to cool naturally, and the material was taken out under an inert gas (nitrogen) environment to obtain a silicon-carbon negative electrode material.

[0054] Comparative Example 3

[0055] This comparative example provides a solid electrolyte-coated silicon-carbon negative electrode material, and the preparation method thereof is different from that of Example 1 only in that the solid electrolyte is an oxide solid electrolyte LaCaO3.

[0056] Comparative Example 4

[0057] This comparative example provides a solid electrolyte / silicon-carbon negative electrode composite material, and its preparation method comprises the following steps: in a glove box, placing silicon-carbon negative electrode material I in a ball mill and ball milling at a speed of 300 rpm for 2 hours to obtain silicon-carbon negative electrode material II; placing solid electrolyte I in a ball mill and ball milling at a speed of 300 rpm for 2 hours to obtain solid electrolyte II; then, the silicon-carbon negative electrode material II and the solid electrolyte II are evenly mixed in a mass ratio of 6:1 to obtain a solid electrolyte / silicon-carbon negative electrode composite material.

[0058] The preparation method of the above-mentioned silicon-carbon negative electrode material I is the same as that in Example 1; the solid electrolyte I is Li2ZrCl4F2, the same as that in Example 1.

[0059] Performance Testing

[0060] The solid electrolyte-coated silicon-carbon negative electrode materials in Examples 1 to 7 and Comparative Examples 2 to 3, the carbon-coated silicon-carbon negative electrode material in Comparative Example 1, and the solid electrolyte / silicon-carbon negative electrode composite material in Comparative Example 4 were mixed with Li6PS5Cl and SP (superpll conductive carbon black) in a mass ratio of 45:50:5 and ground for 30 minutes to form a composite negative electrode material. The composite negative electrode material and Li6PS5Cl (electrolyte) were then cold-pressed (cold-pressed at a pressure of 300 MPa for 3 minutes) to obtain a double-layer structure of negative electrode / electrolyte; the positive electrode material layer side of the positive electrode sheet was then bonded to the electrolyte layer side of the negative electrode / electrolyte, and cold-pressed at a pressure of 200 MPa for 1 minute to obtain a three-layer structure of negative electrode / electrolyte / positive electrode; finally, two stainless steel rods were placed on both sides of the positive and negative electrodes as current collectors to obtain an all-solid-state battery.

[0061] Among them, the above-mentioned positive electrode sheet is prepared by the following method: Li2MnO3 and layered LiCoO2 are mixed evenly in a mass ratio of 6:4 to obtain a lithium-rich manganese-based positive electrode material; then the lithium-rich manganese-based positive electrode material, CNT (carbon nanotube), acetylene carbon black (DENKABLACK Li-435) and PVDF (polyvinylidene fluoride) are mixed in a mass ratio of 97.3:0.5:1:1.2, and then mixed evenly with an appropriate amount of NMP to prepare a positive electrode slurry; then, the positive electrode slurry is evenly coated on aluminum foil, and after drying, rolling and sheeting, a positive electrode sheet is obtained.

[0062] The above-mentioned all-solid-state battery was subjected to the following tests, and the test results are shown in Table 1.

[0063] 1) Initial Coulombic Efficiency: At 25±5°C, the voltage test range is 2.8V-4.3V, and the charge and discharge current is 0.1C / 0.1C. Initial Coulombic Efficiency (%) = (initial discharge capacity / initial charge capacity) × 100%.

[0064] 2) Capacity retention: At 25±5°C, with a voltage range of 2.8V-4.3V, charge and discharge cycles were performed at 0.5C / 0.5C for 30 cycles. The discharge capacity obtained after the first cycle was C0, and the capacity obtained after the 30th cycle was C1. Capacity retention = C1 / C0 × 100%.

[0065] Table 1 Performance of all-solid-state batteries corresponding to various embodiments and comparative examples

[0066]

[0067]

[0068] According to the data in Table 1, the first coulombic efficiency of the all-solid-state batteries corresponding to the solid electrolyte-coated silicon-carbon negative electrode materials in Examples 1 to 7 is greater than 92% and the 30-cycle capacity retention rate is more than 96%, indicating that the solid electrolyte-coated silicon-carbon negative electrode material of the present invention can effectively improve the cycle performance of the all-solid-state battery. At the same time, according to Comparative Examples 1 and 2, it can be seen that simply coating the surface of the silicon-carbon material with a carbon coating layer or a solid electrolyte coating layer cannot effectively improve the cycle performance of the all-solid-state battery. In addition, according to Comparative Examples 3 and 4, it can be found that using an oxide solid electrolyte as the solid electrolyte coating layer or simply physically mixing the carbon-coated silicon-carbon material with the solid electrolyte is also difficult to effectively improve the cycle performance of the all-solid-state battery.

[0069] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A solid electrolyte coated silicon carbon negative electrode material, characterized in that: It comprises a silicon-carbon negative electrode material and a solid electrolyte coating layer provided on the surface of the silicon-carbon negative electrode material; The solid electrolyte coating layer includes at least one of a sulfide electrolyte and a halide electrolyte; The silicon-carbon negative electrode material comprises a core and a carbon coating layer arranged on the surface of the core; the core comprises a porous carbon matrix and a silicon-based material located in the pores of the porous carbon matrix.

2. The solid electrolyte-coated silicon-carbon negative electrode material according to claim 1, characterized in that: The sulfide electrolyte includes Li6PS5X, Li 10 GeP2S 12 、Li7P3S 11 、Li 9.54 Si 1.74 P 1.44 S 11.7 C l0.3 、Li 6.6 Si 0.6 Sb 0.4 At least one of S5I; X in the Li6PS5X is selected from any one of Cl, Br, and I.

3. The solid electrolyte-coated silicon-carbon negative electrode material according to claim 1, characterized in that: The halide electrolyte includes at least one of Li2ZrCl6, Li2HfCl6, Li3YCl6, LiTaCl6, LiNbCl6, LiTaOCl4, and LiNbOCl4.

4. The solid electrolyte-coated silicon-carbon negative electrode material according to claim 1, characterized in that: The solid electrolyte-coated silicon-carbon negative electrode material meets at least one of the following conditions: a. The average particle size of the core is 4 to 8 μm; b. The average thickness of the carbon coating layer is 50 to 300 nm; c. The average thickness of the solid electrolyte coating layer is 50 to 500 nm.

5. The method for preparing the solid electrolyte-coated silicon-carbon negative electrode material according to any one of claims 1 to 4, characterized in that: The following steps are involved: The silicon-carbon negative electrode material and the solid electrolyte are mixed and then ball-milled to obtain a solid electrolyte-coated silicon-carbon negative electrode material; The solid electrolyte includes at least one of a sulfide electrolyte and a halide electrolyte; The silicon-carbon negative electrode material comprises a core and a carbon coating layer arranged on the surface of the core; the core comprises a porous carbon matrix and a silicon-based material located in the pores of the porous carbon matrix.

6. The preparation method according to claim 5, wherein The mass ratio of the silicon-carbon negative electrode material to the solid electrolyte is (2-20):

1.

7. The preparation method according to claim 5, wherein The ball milling process is performed at a rotation speed of 200 to 500 rpm and for a time of 1 to 5 hours.

8. The preparation method according to claim 5, wherein The average particle size of the sulfide electrolyte is 1 to 3 μm; and / or the average particle size of the halide electrolyte is 500 nm to 2 μm.

9. An all-solid-state battery, characterized in that: The solid electrolyte-coated silicon-carbon negative electrode material comprises the solid electrolyte-coated silicon-carbon negative electrode material according to any one of claims 1 to 4.

10. An electrical device, characterized in that: Including the all-solid-state battery according to claim 9, the all-solid-state battery serves as the power supply for the electrical device.

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