Preparation method of silicon-based composite conductive negative electrode and all-solid-state battery

Abstract

The present invention relates to the technical field of solid-state batteries, and discloses a preparation method of a silicon-based composite conductive anode and a all-solid-state battery. The preparation method of the silicon-based composite conductive anode includes the following steps: ball-milling and mixing conductive graphite with a particle size of 1-30 μm and single-walled carbon nanotubes with a length of 3-50 μm to obtain precursor I; ball-milling and mixing precursor I and a silicon-based anode active material to obtain precursor II; ball-milling and mixing precursor II and LiBH4, and after shaping, a silicon-based composite conductive anode is obtained. The preparation method of the present invention can enable the obtained silicon-based composite conductive anode to have high electron and ion transport efficiencies, thereby improving the rate performance and cycle stability of the all-solid-state battery.

Description

Technical Field

[0001] The present invention relates to the technical field of solid-state batteries, and particularly to a preparation method of a silicon-based composite conductive anode and a all-solid-state battery. Background Art

[0002] Lithium-ion batteries perform excellently in the fields of consumer electronics and electric vehicles and have gradually become a key technology for energy storage power grids. Compared with traditional liquid lithium-ion batteries, solid-state lithium batteries have higher stability, safety and energy density, and their development is an important direction for future research.

[0003] Currently, among various anode materials for solid-state lithium batteries, silicon has attracted much attention due to its low alloying potential and theoretical capacity of up to 4200 mAh / g. However, pure silicon faces multiple challenges as a battery material. First, during the lithiation and delithiation processes, the volume change of silicon is significant, resulting in continuous expansion and contraction of particles. This repeated mechanical stress not only generates a large irreversible capacity but also reduces the first Coulombic efficiency, affecting the overall performance of the battery. In addition, the intrinsic conductivity of silicon is low, restricting the transport speeds of electrons and lithium ions and further affecting its rate performance and cycle stability. Therefore, although silicon has a high theoretical specific capacity, it is still difficult to meet the requirements of high-performance batteries in practical applications.

[0004] By pre-lithiation technology for intercalating lithium into the silicon anode (for example, patent CN117199330A adds Li 21 Si5 to the silicon anode), the above-mentioned related problems of the silicon anode can be alleviated. The pre-embedded lithium source can compensate for the lithium consumed due to side reactions and the formation of the solid electrolyte interface (SEI) film, thereby improving the first-cycle Coulombic efficiency and cycle stability of the electrode to a certain extent. However, its effect on improving the electron and ion transport efficiency of the silicon anode is limited, and it cannot well solve the problem of poor rate performance of the silicon anode. Summary of the Invention

[0005] To solve the technical problems of poor rate performance and cycle stability of the silicon anode, the present invention provides a preparation method of a silicon-based composite conductive anode and a all-solid-state battery. The preparation method of the present invention can enable the prepared silicon-based composite conductive anode to have high electron and ion transport efficiency, thereby improving the rate performance and cycle stability of the all-solid-state battery.

[0006] The specific technical solution of the present invention is as follows:

[0007] In a first aspect, the present invention provides a preparation method of a silicon-based composite conductive anode, including the following steps:

[0008] S1: Ball-mill and mix conductive graphite with a particle size of 1 - 30 μm and single-walled carbon nanotubes with a length of 3 - 50 μm to obtain precursor I;

[0009] S2: Mix the precursor I and the silicon-based anode active material by ball milling to obtain precursor II.

[0010] S3: Mix the precursor II and LiBH4 by ball milling, and after shaping, obtain the silicon-based composite conductive anode.

[0011] The silicon-based composite conductive anode prepared by the present invention is added with conductive graphite and single-walled carbon nanotubes. The two can form a bridge through π-π interaction and van der Waals force, and then form a conductive network inside the anode. Moreover, the particle size of the conductive graphite adopted in the present invention is similar to the length of the single-walled carbon nanotubes, which can improve the stability of the conductive network and help maintain a continuous conductive network during the deformation process of the silicon-based anode active material.

[0012] In addition to conductive graphite and single-walled carbon nanotubes, the present invention also adds LiBH4 inside the silicon-based anode, which can reduce the interfacial side reactions between the hydride solid electrolyte and the silicon-based anode in the solid-state battery, thereby avoiding the rapid increase of battery impedance and the rapid attenuation of capacity during the cycling process. At the same time, the hydride solid electrolyte has a low elastic modulus and good mechanical flexibility, and can adapt to the deformation and stress of the silicon-based anode during charge and discharge, thereby reducing the particle breakage of the silicon-based anode during the cycling process, improving the cycling stability of the battery, and reducing its cycling capacity attenuation. In addition, LiBH4 also has a high ionic conductivity, which can improve the transport efficiency of lithium ions inside the silicon-based anode.

[0013] On this basis, in order to give full play to the functions of conductive graphite, single-walled carbon nanotubes and LiBH4 to a greater extent, the present invention makes a special design on the mixing sequence according to the characteristics of these additives. Specifically: the present invention first mixes the conductive graphite and single-walled carbon nanotubes with the silicon-based anode active material by ball milling, and then mixes with LiBH4 by ball milling, which can form a uniform ion-electron transport network everywhere in the prepared anode; if the above four components are ball milled together without considering the order, or the conductive graphite and single-walled carbon nanotubes are first ball milled with LiBH4 and then ball milled with the silicon-based anode active material, due to the difference in electronegativity of the atoms of the materials, the conductive graphite and single-walled carbon nanotubes will preferentially interact with LiBH4, and two types of aggregates, namely conductive graphite + single-walled carbon nanotubes + LiBH4 and silicon-based anode active material, will be formed microscopically, which is not conducive to the construction of a uniform ion-electron transport network everywhere in the anode.

[0014] Preferably, in step S1, the length of the single-walled carbon nanotubes and the particle size of the conductive graphite are both 5 - 20 μm.

[0015] Preferably, in step S1, the diameter of the single-walled carbon nanotubes is 1 to 2 nm; the mass ratio between the single-walled carbon nanotubes and the conductive graphite is 0.11 to 9:1.

[0016] Preferably, in step S2, the silicon-based anode active material is one or two of x LiSi alloy materials and Al / LiH / Li / Si composite materials.

[0017] Compared with the pure Si anode active material, in x LiSi alloy materials and Al / LiH / Li / Si composite materials, by introducing Li, the lithium loss caused by side reactions can be compensated, thereby improving the cycle stability of all-solid-state batteries. In addition, when introducing Li into the Al / LiH / Li / Si composite material, Al and LiH are also introduced, where: Al can improve the conductivity of the silicon-based anode, thereby further improving the cycle performance and rate performance of the battery; the electric field effect between LiH and the Li-Al alloy and Li-Si alloy in the anode can improve the lithium ion transport efficiency in the anode and balance the electric field on the surface of the alloy material, thereby avoiding the growth of lithium dendrites induced by local potential on the material surface, which can further improve the cycle stability of all-solid-state batteries and reduce the cycle capacity attenuation.

[0018] Preferably, in step S2, in the silicon-based anode active material, the molar ratio between Li and Si is 2.3 to 4.4:1 (the Li in this molar ratio does not include the Li in LiH).

[0019] Preferably, the preparation steps of the Al / LiH / Li / Si composite material include: in a vacuum or inert atmosphere, heating a mixture of silicon and lithium aluminum hydride (LiAlH4) with a molar ratio of 2 to 8:1 to 160 to 190 °C and maintaining it for 3 to 6 h, then heating it to 200 to 300 °C and maintaining it for 2 to 5 h, and then mixing it with Li and heat-treating it at 200 to 300 °C for 2 to 4 h.

[0020] In the preparation process of the above Al / LiH / Li / Si composite material, heating at 160 - 190 °C for 3 - 6 h can decompose LiAlH4 into Li3AlH6, Al, and H2; then heating at 200 - 300 °C for 2 - 5 h can further decompose Li3AlH6 into LiH, Al, and H2. By adopting this two-step thermal decomposition method, highly dispersed nano-aluminum particles and nano-LiH particles can be in-situ formed between silicon particles. Among them, the highly dispersed nano-aluminum particles contribute to achieving higher reversibility of the alloying / dealloying reaction, and further improving the cycle stability of the all-solid-state battery to a greater extent; the highly dispersed nano-LiH particles can reduce the local potential difference at each point on the surface of the Li-Al alloy and Li-Si alloy, which helps to improve the lithium-ion transport efficiency by utilizing the electric field effect between the LiH particles and the Li-Al alloy and Li-Si alloy, thereby achieving better battery cycle stability.

[0021] In the Al / LiH / Li / Si composite material, when the doping amounts of Al and LiH are too low, the cycle stability of the all-solid-state battery cannot be effectively improved, and even the cycle stability will be reduced. In the preparation process of the Al / LiH / Li / Si composite material of the present invention, by designing the molar ratio of silicon to lithium aluminum hydride as 2 - 8:1, the cycle stability of the all-solid-state battery can be effectively improved. In addition, in the entire preparation process of the Al / LiH / Li / Si composite material of the present invention, the temperature of each stage of heat treatment is not higher than 300 °C, which can avoid the further decomposition of LiH into Li, is conducive to better controlling the doping amount of LiH in the negative electrode, and realizes the improvement of the cycle stability of the all-solid-state battery.

[0022] Preferably, the preparation step of the mixture of silicon and lithium aluminum hydride includes: grinding and mixing silicon and lithium aluminum hydride, and then performing high-energy ball milling; the conditions of the high-energy ball milling are as follows: the ball-to-material ratio is 60 - 120:1, the rotation speed is 200 - 500 rpm, and the time is 1 - 5 h.

[0023] Preferably, the method of mixing with Li is ball milling, and the conditions are as follows: the ball-to-material ratio is 60 - 120:1, the rotation speed is 100 - 200 rpm, and the time is 30 - 60 min.

[0024] Preferably, the mass ratio among the silicon-based negative electrode active material, the first precursor material, and the solid electrolyte is 50 - 80:10 - 25:10 - 25.

[0025] Preferably, in steps S1 - S3, the conditions of the ball milling and mixing are as follows: the ball-to-material ratio is 60 - 120:1, the rotation speed is 100 - 1200 rpm, and the time is 2 - 30 h.

[0026] Preferably, in step S3, the forming method is: pressing and forming on one side of the solid electrolyte sheet.

[0027] In a second aspect, the present invention provides a all-solid-state battery, including a silicon-based composite conductive negative electrode prepared by the preparation method.

[0028] Preferably, the all-solid-state battery includes a positive electrode, a hydride solid electrolyte sheet, and a silicon-based composite conductive negative electrode stacked in sequence; the positive electrode includes a positive electrode active material, a conductive agent, and a hydride solid electrolyte, and the positive electrode active material includes one or more of S, Se, Li2S, Li2Se, and sulfurized polyacrylonitrile (SPAN).

[0029] Compared with the prior art, the present invention has the following advantages:

[0030] (1) By adding conductive graphite, single-walled carbon nanotubes, and LiBH4 to the silicon-based negative electrode and cooperating with a specific preparation method, the present invention can form a uniform ion-electron transport network everywhere in the silicon-based negative electrode, thereby endowing the all-solid-state battery with better rate performance and cycle stability.

[0031] (2) The present invention uses an Al / LiH / Li / Si composite material as the negative electrode active material. By doping with Al and LiH therein, the cycle stability of the all-solid-state battery can be further improved; moreover, by preparing the Al / LiH / Li / Si composite material by a specific method, the cycle performance of the battery can reach a higher level. Specific Embodiments

[0032] The present invention will be further described below in conjunction with embodiments.

[0033] A preparation method of a silicon-based composite conductive negative electrode includes the following steps:

[0034] S1: Ball-milling and mixing conductive graphite with a particle size of 1-30 μm and single-walled carbon nanotubes with a length of 3-50 μm to obtain a precursor I;

[0035] S2: Ball-milling and mixing the precursor I and the silicon-based negative electrode active material to obtain a precursor II;

[0036] S3: Ball-milling and mixing the precursor II and LiBH4, and after forming, obtaining a silicon-based composite conductive negative electrode.

[0037] As a specific embodiment, the mass ratio among the silicon-based negative electrode active material, the first precursor material, and the solid electrolyte is 50-80:10-25:10-25.

[0038] As a specific embodiment, in step S1, the length of the single-walled carbon nanotubes and the particle size of the conductive graphite are both 5-20 μm.

[0039] As a specific embodiment, in step S1, the diameter of the single-walled carbon nanotubes is 1 to 2 nm; the mass ratio between the single-walled carbon nanotubes and the conductive graphite is 0.11 to 9:1.

[0040] As a specific embodiment, in step S2, the silicon-based anode active material is one or two of Li x Si alloy material and Al / LiH / Li / Si composite material, wherein the molar ratio between Li and Si is 2.3 to 4.4:1; the preparation steps of the Al / LiH / Li / Si composite material include: in a vacuum or inert atmosphere, heating a mixture of silicon and lithium aluminum hydride (LiAlH4) with a molar ratio of 2 to 8:1 to 160 to 190 °C and maintaining for 3 to 6 h, then heating to 200 to 300 °C and maintaining for 2 to 5 h, and then mixing with Li and heat-treating at 200 to 300 °C for 2 to 4 h.

[0041] In the preparation steps of the above Al / LiH / Li / Si composite material, optionally or preferably:

[0042] The preparation steps of the mixture of silicon and lithium aluminum hydride include: grinding and mixing silicon and lithium aluminum hydride, and then performing high-energy ball milling; the conditions of the high-energy ball milling are as follows: the ball-to-material ratio is 60 to 120:1, the rotation speed is 200 to 500 rpm, and the time is 1 to 5 h;

[0043] The way of mixing with Li is ball milling, and the conditions are as follows: the ball-to-material ratio is 60 to 120:1, the rotation speed is 100 to 200 rpm, and the time is 30 to 60 min.

[0044] As a specific embodiment, in steps S1 to S3, the conditions of the ball milling and mixing are as follows: the ball-to-material ratio is 60 to 120:1, the rotation speed is 100 to 1200 rpm, and the time is 2 to 30 h.

[0045] As a specific embodiment, in step S3, the forming method is: pressing and forming on one side of the solid electrolyte sheet.

[0046] A all-solid-state battery includes a silicon-based composite conductive anode prepared by the above preparation method.

[0047] As a specific embodiment, the all-solid-state battery includes a positive electrode, a hydride solid electrolyte sheet, and a silicon-based composite conductive anode stacked in sequence; the positive electrode includes a positive electrode active material, a conductive agent, and a hydride solid electrolyte, and the positive electrode active material includes one or more of S, Se, Li2S, Li2Se, and sulfurized polyacrylonitrile (SPAN).

[0048] The present invention will be described below through specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and not to limit the scope of the present invention. Without departing from the spirit and scope of the inventive concept, changes and advantages that can be conceived by those skilled in the art are included in the present invention, and the scope of protection of the present invention is defined by the appended claims and any equivalents thereof.

[0049] Example 1

[0050] The silicon-based composite conductive anode and all-solid-state battery of this example are prepared through the following steps:

[0051] S1: Prepare the silicon-based composite conductive anode material

[0052] Single-walled carbon nanotubes (length 5 - 20 μm, diameter 1 - 2 nm) and conductive graphite (particle size 5 - 20 μm) are mixed in a mass ratio of 1:1, placed in a stainless steel ball milling tank, and ball milled for 2 h under an argon atmosphere with a ball-to-material ratio of 100:1 and a rotation speed of 400 rpm to obtain precursor I. Then, Li 2.3 Si alloy material with a mass twice that of precursor I is added to the stainless steel ball milling tank, and ball milling is continued for 2 h under an argon atmosphere with a ball-to-material ratio of 100:1 and a rotation speed of 400 rpm to obtain precursor II. Finally, LiBH4 with a mass of 1 / 3 of precursor II is added to the stainless steel ball milling tank, and ball milling is carried out for 10 h under an argon atmosphere with a ball-to-material ratio of 100:1 and a rotation speed of 600 rpm to obtain the silicon-based composite conductive anode material.

[0053] S2: Prepare the all-solid-state battery

[0054] S, conductive carbon black (Super P), and LiBH4 are mixed in a mass ratio of 3:3:4 to obtain the cathode material. The hydride electrolyte LiBH4 is pressed into a sheet under a pressure of 300 MPa to obtain a solid electrolyte sheet. The silicon-based composite conductive anode material is pressed into a sheet on one side of the solid electrolyte sheet under a pressure of 50 MPa to form a silicon-based composite conductive anode. The cathode material is pressed into a sheet on the other side of the solid electrolyte sheet under a pressure of 50 MPa to form a cathode, and an all-solid-state battery is obtained.

[0055] Example 2

[0056] The difference between this example and Example 1 is only that the Li 2.3 Si alloy material is replaced with an Al / LiH / Li / Si composite material. Specifically, the silicon-based composite conductive anode and all-solid-state battery of this example are prepared through the following steps:

[0057] S1: Prepare the Al / LiH / Li / Si composite material

[0058] Put silicon powder and lithium aluminum hydride powder in a mortar according to a molar ratio of 8:1, grind them to mix evenly, then transfer them to a stainless steel ball milling tank. Under the conditions of an argon atmosphere, a ball-to-material ratio of 100:1, and a rotation speed of 400 rpm, ball mill for 2 h to obtain a Si / LiAlH4 mixture. Transfer the Si / LiAlH4 mixture into a stainless steel tube, maintain the vacuum degree in the tube at not less than 10 kPa during subsequent heat treatment, heat up to 160 °C and maintain for 6 h, continue to heat up to 300 °C and maintain for 2 h, and then cool to room temperature to obtain an Al / LiH / Si composite material. Weigh lithium powder with a molar amount 2.3 times that of silicon powder, put it together with the Al / LiH / Si composite material in a stainless steel ball milling tank, under the conditions of an argon atmosphere, a ball-to-material ratio of 100:1, and a rotation speed of 100 rpm, ball mill for 40 min, then transfer it to a stainless steel tube, and heat up to 300 °C in an argon atmosphere and maintain for 3 h to obtain an Al / LiH / Li / Si composite material.

[0059] S2: Preparation of silicon-based composite conductive anode material

[0060] Mix single-walled carbon nanotubes (length 5 - 20 μm, diameter 1 - 2 nm) and conductive graphite (particle size 5 - 20 μm) according to a mass ratio of 1:1, put them in a stainless steel ball milling tank, under the conditions of an argon atmosphere, a ball-to-material ratio of 100:1, and a rotation speed of 400 rpm, ball mill for 2 h to obtain precursor I. Then add Al / LiH / Li / Si composite material with a mass 2 times that of precursor I to the stainless steel ball milling tank, and continue to ball mill for 2 h under the conditions of an argon atmosphere, a ball-to-material ratio of 100:1, and a rotation speed of 400 rpm to obtain precursor II. Finally, add LiBH4 with a mass 1 / 3 of that of precursor II to the stainless steel ball milling tank, and ball mill for 10 h under the conditions of an argon atmosphere, a ball-to-material ratio of 100:1, and a rotation speed of 600 rpm to obtain the silicon-based composite conductive anode material.

[0061] S3: Preparation of all-solid-state battery

[0062] Mix S, conductive carbon black (Super P) and LiBH4 according to a mass ratio of 3:3:4 to obtain the cathode material. Press the hydride electrolyte LiBH4 into a sheet under a pressure of 300 MPa to obtain a solid electrolyte sheet. Press the silicon-based composite conductive anode material into a sheet on one side of the solid electrolyte sheet under a pressure of 50 MPa to form a silicon-based composite conductive anode. Press the cathode material into a sheet on the other side of the solid electrolyte sheet under a pressure of 50 MPa to form a cathode, and obtain an all-solid-state battery.

[0063] Example 3

[0064] The difference between this example and Example 1 is only that: Li 2.3Replace the Si alloy material with an Al / LiH / Li / Si composite material. Specifically, the silicon-based composite conductive anode and the all-solid-state battery of this embodiment are prepared through the following steps:

[0065] S1: Prepare the Al / LiH / Li / Si composite material

[0066] Place silicon powder and lithium aluminum hydride powder in a mortar according to a molar ratio of 2:1. After grinding to mix them evenly, transfer them to a stainless steel ball milling jar. Under an argon atmosphere, with a ball-to-material ratio of 100:1 and a rotation speed of 400 rpm, ball mill for 2 h to obtain a Si / LiAlH4 mixture. Transfer the Si / LiAlH4 mixture into a stainless steel tube, maintain the vacuum in the tube at no less than 10 kPa during subsequent heat treatment, heat up to 180 °C and maintain for 3 h, continue to heat up to 210 °C and maintain for 5 h, and then cool to room temperature to obtain the Al / LiH / Si composite material. Weigh lithium powder with a molar amount 2.3 times that of the silicon powder, place it together with the Al / LiH / Si composite material in a stainless steel ball milling jar, under an argon atmosphere, with a ball-to-material ratio of 100:1 and a rotation speed of 100 rpm, ball mill for 40 min, then transfer it into a stainless steel tube, and heat up to 300 °C under an argon atmosphere and maintain for 3 h to obtain the Al / LiH / Li / Si composite material.

[0067] S2: Prepare the silicon-based composite conductive anode material

[0068] Mix single-walled carbon nanotubes (with a length of 5 - 20 μm and a diameter of 1 - 2 nm) and conductive graphite (with a particle size of 5 - 20 μm) according to a mass ratio of 1:1, place them in a stainless steel ball milling jar, under an argon atmosphere, with a ball-to-material ratio of 100:1 and a rotation speed of 400 rpm, ball mill for 2 h to obtain precursor I. Then add Al / LiH / Li / Si composite material with a mass 2 times that of precursor I to the stainless steel ball milling jar, and continue to ball mill for 2 h under an argon atmosphere, with a ball-to-material ratio of 100:1 and a rotation speed of 400 rpm to obtain precursor II. Finally, add LiBH4 with a mass 1 / 3 that of precursor II to the stainless steel ball milling jar, and ball mill for 10 h under an argon atmosphere, with a ball-to-material ratio of 100:1 and a rotation speed of 600 rpm to obtain the silicon-based composite conductive anode material.

[0069] S3: Prepare the all-solid-state battery

[0070] S, conductive carbon black (Super P), and LiBH4 were mixed in a mass ratio of 3:3:4 to obtain the cathode material. The hydride electrolyte LiBH4 was pressed into a sheet under a pressure of 300 MPa to obtain a solid electrolyte sheet. The silicon-based composite conductive anode material was pressed into a sheet on one side of the solid electrolyte sheet under a pressure of 50 MPa to form a silicon-based composite conductive anode. The cathode material was pressed into a sheet on the other side of the solid electrolyte sheet under a pressure of 50 MPa to form the cathode, and a all-solid-state battery was obtained.

[0071] Example 4

[0072] The difference between this example and Example 2 is only that: the molar ratio of silicon powder and lithium aluminum hydride powder was changed from 8:1 to 18:1. Specifically, the silicon-based composite conductive anode and the all-solid-state battery of this example were prepared by the following steps:

[0073] S1: Prepare the Al / LiH / Li / Si composite material

[0074] Silicon powder and lithium aluminum hydride powder were placed in a mortar according to a molar ratio of 18:1, ground and mixed evenly, then transferred to a stainless steel ball milling jar. Under an argon atmosphere, with a ball-to-material ratio of 100:1 and a rotation speed of 400 rpm, ball milling was carried out for 2 h to obtain a Si / LiAlH4 mixture. The Si / LiAlH4 mixture was transferred into a stainless steel tube, and the vacuum degree inside the tube was maintained at not less than 10 kPa during the subsequent heat treatment. The temperature was raised to 160 °C and maintained for 6 h, then continued to be raised to 300 °C and maintained for 2 h, and then cooled to room temperature to obtain an Al / LiH / Si composite material. Lithium powder with a molar amount 2.3 times that of the silicon powder was weighed and placed together with the Al / LiH / Si composite material in a stainless steel ball milling jar. Under an argon atmosphere, with a ball-to-material ratio of 100:1 and a rotation speed of 100 rpm, after ball milling for 40 min, it was transferred into a stainless steel tube, and the temperature was raised to 300 °C under an argon atmosphere and maintained for 3 h to obtain an Al / LiH / Li / Si composite material.

[0075] S2: Prepare the silicon-based composite conductive anode material

[0076] Mix single-walled carbon nanotubes (with a length of 5 - 20 μm and a diameter of 1 - 2 nm) and conductive graphite (with a particle size of 5 - 20 μm) in a mass ratio of 1:1, place them in a stainless-steel ball-milling jar, and ball-mill for 2 h under the conditions of an argon atmosphere, a ball-to-material ratio of 100:1, and a rotation speed of 400 rpm to obtain precursor I. Then, add an Al / LiH / Li / Si composite material with a mass twice that of precursor I to the stainless-steel ball-milling jar, and continue to ball-mill for 2 h under the conditions of an argon atmosphere, a ball-to-material ratio of 100:1, and a rotation speed of 400 rpm to obtain precursor II. Finally, add LiBH4 with a mass of 1 / 3 of precursor II to the stainless-steel ball-milling jar, and ball-mill for 10 h under the conditions of an argon atmosphere, a ball-to-material ratio of 100:1, and a rotation speed of 600 rpm to obtain the silicon-based composite conductive anode material.

[0077] S3: Prepare all-solid-state battery

[0078] Mix S, conductive carbon black (Super P), and LiBH4 in a mass ratio of 3:3:4 to obtain the cathode material. Press the hydride electrolyte LiBH4 into a sheet under a pressure of 300 MPa to obtain the solid-state electrolyte sheet. Press the silicon-based composite conductive anode material into a sheet on one side of the solid-state electrolyte sheet under a pressure of 50 MPa to form the silicon-based composite conductive anode. Press the cathode material into a sheet on the other side of the solid-state electrolyte sheet under a pressure of 50 MPa to form the cathode, and obtain the all-solid-state battery.

[0079] Example 5

[0080] The difference between this example and Example 2 is only that: in step S1, LiAlH4 is decomposed into Al and LiH by a one-step thermal decomposition method. Specifically, the silicon-based composite conductive anode and the all-solid-state battery of this example are prepared through the following steps:

[0081] S1: Prepare Al / LiH / Li / Si composite material

[0082] Put silicon powder and lithium aluminum hydride powder in a mortar according to a molar ratio of 8:1, grind them to mix evenly, then transfer them to a stainless steel ball milling tank. Under an argon atmosphere, with a ball-to-material ratio of 100:1 and a rotation speed of 400 rpm, ball mill for 2 h to obtain a Si / LiAlH4 mixture. Transfer the Si / LiAlH4 mixture into a stainless steel tube, maintain the vacuum in the tube at no less than 10 kPa during subsequent heat treatment, heat up to 300 °C and maintain for 8 h, and then cool to room temperature to obtain an Al / LiH / Si composite material. Weigh lithium powder with a molar amount 2.3 times that of silicon powder, put it together with the Al / LiH / Si composite material in a stainless steel ball milling tank, under an argon atmosphere, with a ball-to-material ratio of 100:1 and a rotation speed of 100 rpm, ball mill for 40 min, then transfer it to a stainless steel tube, and heat up to 300 °C and maintain for 3 h under an argon atmosphere to obtain an Al / LiH / Li / Si composite material.

[0083] S2: Preparation of silicon-based composite conductive anode material

[0084] Mix single-walled carbon nanotubes (with a length of 5 - 20 μm and a diameter of 1 - 2 nm) and conductive graphite (with a particle size of 5 - 20 μm) according to a mass ratio of 1:1, put them in a stainless steel ball milling tank, under an argon atmosphere, with a ball-to-material ratio of 100:1 and a rotation speed of 400 rpm, ball mill for 2 h to obtain precursor I. Then add Al / LiH / Li / Si composite material with a mass 2 times that of precursor I to the stainless steel ball milling tank, and continue to ball mill for 2 h under an argon atmosphere, with a ball-to-material ratio of 100:1 and a rotation speed of 400 rpm to obtain precursor II. Finally, add LiBH4 with a mass 1 / 3 of that of precursor II to the stainless steel ball milling tank, and ball mill for 10 h under an argon atmosphere, with a ball-to-material ratio of 100:1 and a rotation speed of 600 rpm to obtain the silicon-based composite conductive anode material.

[0085] S3: Preparation of all-solid-state battery

[0086] Mix S, conductive carbon black (Super P) and LiBH4 according to a mass ratio of 3:3:4 to obtain the cathode material. Press the hydride electrolyte LiBH4 into a sheet under a pressure of 300 MPa to obtain a solid electrolyte sheet. Press the silicon-based composite conductive anode material onto one side of the solid electrolyte sheet under a pressure of 50 MPa to form a silicon-based composite conductive anode. Press the cathode material onto the other side of the solid electrolyte sheet under a pressure of 50 MPa to form a cathode, and obtain an all-solid-state battery.

[0087] Example 6

[0088] The difference between this example and Example 2 is only that: in step S2, the temperature of the second-stage thermal decomposition of LiAlH4 is changed from 300 °C to 450 °C. Specifically, the silicon-based composite conductive anode and all-solid-state battery of this example are prepared through the following steps:

[0089] S1: Preparation of Al / LiH / Li / Si composite material

[0090] Put silicon powder and lithium aluminum hydride powder in a mortar according to a molar ratio of 8:1, grind them to mix evenly, then transfer them to a stainless steel ball milling tank. Under the conditions of an argon atmosphere, a ball-to-material ratio of 100:1, and a rotation speed of 400 rpm, ball mill for 2 h to obtain a Si / LiAlH4 mixture. Transfer the Si / LiAlH4 mixture into a stainless steel tube, maintain the vacuum degree in the tube at not less than 10 kPa during subsequent heat treatment, heat up to 160 °C and maintain for 6 h, continue to heat up to 450 °C and maintain for 2 h, and then cool to room temperature to obtain an Al / LiH / Si composite material. Weigh lithium powder with a molar amount 2.3 times that of silicon powder, put it together with the Al / LiH / Si composite material into a stainless steel ball milling tank, under the conditions of an argon atmosphere, a ball-to-material ratio of 100:1, and a rotation speed of 100 rpm, ball mill for 40 min, then transfer it into a stainless steel tube, and heat up to 300 °C in an argon atmosphere and maintain for 3 h to obtain an Al / LiH / Li / Si composite material.

[0091] S2: Preparation of silicon-based composite conductive anode material

[0092] Mix single-walled carbon nanotubes (length 5 - 20 μm, diameter 1 - 2 nm) and conductive graphite (particle size 5 - 20 μm) according to a mass ratio of 1:1, put them in a stainless steel ball milling tank, under the conditions of an argon atmosphere, a ball-to-material ratio of 100:1, and a rotation speed of 400 rpm, ball mill for 2 h to obtain precursor I. Then add Al / LiH / Li / Si composite material with a mass 2 times that of precursor I to the stainless steel ball milling tank, and continue to ball mill for 2 h under the conditions of an argon atmosphere, a ball-to-material ratio of 100:1, and a rotation speed of 400 rpm to obtain precursor II. Finally, add LiBH4 with a mass 1 / 3 of precursor II to the stainless steel ball milling tank, and ball mill for 10 h under the conditions of an argon atmosphere, a ball-to-material ratio of 100:1, and a rotation speed of 600 rpm to obtain a silicon-based composite conductive anode material.

[0093] S3: Preparation of all-solid-state battery

[0094] Mix S, conductive carbon black (Super P) and LiBH4 according to a mass ratio of 3:3:4 to obtain a positive electrode material. Press the hydride electrolyte LiBH4 into a sheet under a pressure of 300 MPa to obtain a solid electrolyte sheet. Press the silicon-based composite conductive anode material onto one side of the solid electrolyte sheet under a pressure of 50 MPa to form a silicon-based composite conductive anode. Press the positive electrode material onto the other side of the solid electrolyte sheet under a pressure of 50 MPa to form a positive electrode, and obtain an all-solid-state battery.

[0095] Comparative Example 1

[0096] The difference between this comparative example and Example 1 is only that: the single-walled carbon nanotubes (with a length of 5 - 20 μm and a diameter of 1 - 2 nm) are replaced with single-walled carbon nanotubes (with a length of 1 - 2 μm and a diameter of 1 - 2 nm). Specifically, the silicon-based composite conductive anode and the all-solid-state battery of this comparative example are prepared through the following steps:

[0097] S1: Prepare the silicon-based composite conductive anode material

[0098] Mix single-walled carbon nanotubes (with a length of 1 - 2 μm and a diameter of 1 - 2 nm) and conductive graphite (with a particle size of 5 - 20 μm) in a mass ratio of 1:1, place them in a stainless-steel ball-milling tank, and ball-mill for 2 h under the conditions of an argon atmosphere, a ball-to-material ratio of 100:1, and a rotation speed of 400 rpm to obtain precursor I. Then, add Li 2.3 Si alloy material with a mass twice that of precursor I into the stainless-steel ball-milling tank, and continue to ball-mill for 2 h under the conditions of an argon atmosphere, a ball-to-material ratio of 100:1, and a rotation speed of 400 rpm to obtain precursor II. Finally, add LiBH4 with a mass of 1 / 3 of precursor II into the stainless-steel ball-milling tank, and ball-mill for 10 h under the conditions of an argon atmosphere, a ball-to-material ratio of 100:1, and a rotation speed of 600 rpm to obtain the silicon-based composite conductive anode material.

[0099] S2: Prepare the all-solid-state battery

[0100] Mix S, conductive carbon black (Super P) and LiBH4 in a mass ratio of 3:3:4 to obtain the cathode material. Press the hydride electrolyte LiBH4 into a sheet under a pressure of 300 MPa to obtain a solid electrolyte sheet. Press the silicon-based composite conductive anode material onto one side of the solid electrolyte sheet under a pressure of 50 MPa to form a silicon-based composite conductive anode. Press the cathode material onto the other side of the solid electrolyte sheet under a pressure of 50 MPa to form a cathode, and obtain the all-solid-state battery.

[0101] Comparative Example 2

[0102] The difference between this comparative example and Example 1 is only that: in step S1, single-walled carbon nanotubes, conductive graphite, Li 2.3 Si alloy material and LiBH4 are ball-milled and mixed in one step. Specifically, the silicon-based composite conductive anode and the all-solid-state battery of this comparative example are prepared through the following steps:

[0103] S1: Prepare the silicon-based composite conductive anode material

[0104] Mix single-walled carbon nanotubes (with a length of 5 - 20 μm and a diameter of 1 - 2 nm), conductive graphite (with a particle size of 5 - 20 μm), Li 2.3The Si alloy material and LiBH4 are mixed at a mass ratio of 1:1:4:2, placed in a stainless steel ball milling jar, and ball milled for 10 h under the conditions of an argon atmosphere, a ball-to-material ratio of 100:1, and a rotation speed of 600 rpm to obtain a silicon-based composite conductive anode material.

[0105] S2: Preparation of all-solid-state battery

[0106] S, conductive carbon black (Super P), and LiBH4 are mixed at a mass ratio of 3:3:4 to obtain a cathode material. The hydride electrolyte LiBH4 is pressed into a sheet under a pressure of 300 MPa to obtain a solid electrolyte sheet. The silicon-based composite conductive anode material is pressed into a sheet on one side of the solid electrolyte sheet under a pressure of 50 MPa to form a silicon-based composite conductive anode. The cathode material is pressed into a sheet on the other side of the solid electrolyte sheet under a pressure of 50 MPa to form a cathode, and an all-solid-state battery is obtained.

[0107] Test examples

[0108] Take the all-solid-state batteries prepared in each example and comparative example, and perform performance tests according to the following method:

[0109] (1) Cycling performance: Under the conditions of a temperature of 120 °C, a charge-discharge current of 0.1C, and a pressure of 50 MPa, after 50 charge-discharge cycles, the initial Coulomb efficiency and the capacity retention rate after 50 cycles are detected.

[0110] (2) Rate performance: Charge at a current of 0.1C, and discharge at currents of 0.1C, 0.2C, 0.5C, 1C, and 2C respectively. The cut-off voltage for charging is 3V, and the cut-off voltage for discharging is 0.1V. The discharge specific capacity at different discharge currents is detected.

[0111] The performance test results of the all-solid-state battery are shown in Table 1.

[0112] Table 1 Performance test results of all-solid-state battery

[0113]

[0114] Analyzing the test results in Table 1, it can be seen that:

[0115] (1) The initial Coulomb efficiency, cycling stability, and rate performance of the all-solid-state battery in Example 1 are superior to those in Comparative Example 1. The reason for the analysis is that: the length of the single-walled carbon nanotubes used in Example 1 is similar to the particle size of the conductive graphite, which can make the formed conductive network more stable and contribute to maintaining a continuous conductive network during the deformation process of the anode active material.

[0116] (2) The initial Coulombic efficiency, cycle stability, and rate performance of the all-solid-state battery of Example 1 are superior to those of Comparative Example 2. The reason for the analysis is as follows: In Comparative Example 2, single-walled carbon nanotubes, conductive graphite, Li 2.3 Si alloy material, and LiBH4 were ball-milled and mixed in one step without considering the order. Due to the difference in electronegativity of the atoms of the materials, conductive graphite and single-walled carbon nanotubes would preferentially interact with LiBH4, forming two types of aggregates, namely conductive graphite + single-walled carbon nanotubes + LiBH4 and silicon-based anode active material, microscopically, which is not conducive to the construction of a uniform ion-electron transport network throughout the anode.

[0117] (3) The cycle stability and rate performance of the all-solid-state batteries of Examples 2 and 3 are superior to those of Example 1. The reason for the analysis is as follows: In the silicon-based anode active materials used in Examples 2 and 3, Al and LiH were doped. Among them, Al can improve the electrical conductivity of the silicon-based anode, thereby further improving the cycle performance and rate performance of the battery; the electric field effect between LiH and the Li-Al alloy and Li-Si alloy in the anode can improve the lithium-ion transport efficiency in the anode and balance the electric field on the surface of the alloy material, thereby avoiding the growth of lithium dendrites induced by the local potential on the material surface, which can further improve the cycle stability of the all-solid-state battery and reduce the cycle capacity attenuation.

[0118] (4) The cycle stability and rate performance of the all-solid-state battery of Example 4 are worse than those of Example 2 and lower than those of Example 1. It shows that when the amount of LiAlH4 is too small, the doping amounts of Al and LiH in the silicon-based anode active material are too small, which will instead cause a decrease in the cycle stability and rate performance of the battery.

[0119] (5) The cycle stability and rate performance of the all-solid-state battery of Example 5 are lower than those of Example 2 and lower than those of Example 1. The reason for the analysis is as follows: In the process of preparing the Al / LiH / Li / Si composite material in Example 5, LiAlH4 was decomposed into Al and LiH by one-step thermal decomposition, and the formed LiH particles had a relatively large size, which would lead to a large local potential difference at each point on the surface of the Li-Al alloy and Li-Si alloy, and the lithium-ion transport efficiency in the anode was relatively low. Even in the system of the present invention, it would cause the cycle stability and rate performance of the battery to be lower than the case where Al and LiH were not introduced.

[0120] (6)The cycle stability of the all-solid-state battery in Example 6 is lower than that in Example 2 and lower than that in Example 1. The reason for the analysis is as follows: In the process of preparing the Al / LiH / Li / Si composite material in Example 6, an excessively high heat treatment temperature is adopted, which will cause LiH to further decompose into Li, and it is impossible to utilize the electric field effect between LiH and the Li-Al alloy and Li-Si alloy in the negative electrode to promote lithium ion transport, and balance the electric field on the surface of the alloy material to reduce the growth of lithium dendrites. Even in the system of the present invention, it will cause the cycle stability and rate performance of the battery to be lower than the case where Al and LiH are not introduced.

[0121] The raw materials and equipment used in the present invention are all common raw materials and equipment in the art without special instructions; the methods used in the present invention are all conventional methods in the art without special instructions.

[0122] The above are only the preferred embodiments of the present invention, and do not impose any limitations on the present invention. Any simple modifications, changes, and equivalent transformations made to the above embodiments according to the technical essence of the present invention still belong to the protection scope of the technical solution of the present invention.

Claims

1. A method for preparing a silicon-based composite conductive negative electrode, characterized in that: The following steps are involved: S1: ball-milling and mixing conductive graphite with a particle size of 5 to 20 μm and single-walled carbon nanotubes with a length of 5 to 20 μm to obtain precursor I; S2: ball-milling the precursor I and the silicon-based negative electrode active material to obtain the precursor II; S3: Precursor II and LiBH4 are mixed by ball milling, and after forming, a silicon-based composite conductive negative electrode is obtained.

2. The preparation method according to claim 1, characterized in that: In step S1, the diameter of the single-walled carbon nanotube is 1-2 nm; and the mass ratio between the single-walled carbon nanotube and the conductive graphite is 0.11-9:

1.

3. The preparation method according to claim 1, characterized in that: In step S2, the silicon-based negative electrode active material is Li x Si alloy materials and / or Al / LiH / Li / Si composite materials.

4. The preparation method according to claim 3, characterized in that: In step S2, in the silicon-based negative electrode active material, the molar ratio between Li and Si is 2.3-4.4:

1.

5. The preparation method according to claim 3 or 4, characterized in that: The preparation steps of the Al / LiH / Li / Si composite material include: in a vacuum or inert atmosphere, heating a mixture of silicon and lithium aluminum hydride in a molar ratio of 2-8:1 to 160-190° C. and maintaining it for 3-6 hours, then heating it to 200-300° C. and maintaining it for 2-5 hours, and then mixing it with Li and heat treating it at 200-300° C. for 2-4 hours.

6. The preparation method according to claim 5, characterized in that: The mixing method with Li is ball milling, and the conditions are as follows: the ball-to-material ratio is 60-120:1, the rotation speed is 100-200 rpm, and the time is 30-60 min.

7. The preparation method according to claim 1, characterized in that: The mass ratio of the silicon-based negative electrode active material, the precursor I and LiBH4 is 50~80:10~25:10~25.

8. The preparation method according to claim 1, characterized in that: In steps S1 to S3, the conditions for ball milling are as follows: ball-to-material ratio is 60 to 120:1, rotation speed is 100 to 1200 rpm, and time is 2 to 30 hours.

9. An all-solid-state battery, characterized in that: It comprises a silicon-based composite conductive negative electrode prepared by the preparation method according to any one of claims 1 to 8.

10. The all-solid-state battery according to claim 9, characterized in that: It includes a positive electrode, a hydride solid electrolyte sheet and a silicon-based composite conductive negative electrode stacked in sequence; the positive electrode includes a positive electrode active material, a conductive agent and a hydride solid electrolyte, and the positive electrode active material includes one or more of S, Se, Li2S, Li2Se and sulfide polyacrylonitrile.

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