An Al- and LiH-codoped silicon anode material, its preparation method and application

Abstract

The present invention relates to the field of battery electrode materials, and discloses an Al- and LiH-codoped silicon anode material, a preparation method thereof, and an application thereof. The preparation method comprises the following steps: after Si and LiAlH4 are subjected to powder pressing, vacuum heat treatment is carried out at 160-190 °C for 3-6 h, and then vacuum heat treatment is carried out at 200-300 °C for 2-5 h to obtain the Al- and LiH-codoped silicon anode material. By forming metal aluminum and lithium hydride codoping in the silicon anode material through a specific method, the present invention can endow a lithium ion battery with higher initial Coulomb efficiency and cycling stability.

Description

Technical Field

[0001] The present invention relates to the field of battery electrode materials, and particularly to an Al- and LiH-codoped silicon anode material, its preparation method and application. Background Art

[0002] Silicon anode materials are regarded as one of the most promising anode materials for lithium-ion batteries due to their abundant natural resources in the earth's crust, low redox voltage, and high theoretical specific capacity. However, the main challenges faced by silicon anodes during the electrochemical cycling process include significant volume changes and adverse interfacial reactions, which seriously weaken the cycling stability of the battery. At the same time, the low electronic conductivity of silicon further exacerbates the kinetic barriers of the electrode reaction, restricting the efficient transport of lithium ions and thus affecting the overall performance of the battery. These problems constitute the main obstacles to the commercial application of silicon anode materials in rechargeable lithium-ion batteries.

[0003] To overcome the above problems, common strategies currently include using silicon nanoparticles with porous structures, surface coating technologies, functional electrolytes or conductive additives, and designing new binders, aiming to enhance the cycling stability of the electrode materials. Nevertheless, due to the significant volume changes of silicon during charge and discharge, using silicon alone still faces many challenges. Patent CN116404131A discloses a silicon-carbon anode material with a nano-homogeneous structure, its preparation method and application. Using fumed silica, lithium aluminum hydride and hard carbon materials as raw materials, sintering is carried out, and then soft carbon material coating, roasting, crushing and shaping are carried out to obtain a silicon-carbon anode material in which nano-silicon is uniformly distributed inside the hard carbon matrix and a lithium metaaluminate film is wrapped on the surface of the nano-silicon, and a soft carbon coating layer exists on the surface of the hard carbon matrix. The doping of lithium metaaluminate in the silicon-carbon anode material in this patent improves the first Coulombic efficiency and cycling stability of the battery to a certain extent, but the effect is limited. Summary of the Invention

[0004] To solve the technical problems of poor first Coulombic efficiency and cycling stability of batteries using silicon anode materials, the present invention provides an Al- and LiH-codoped silicon anode material, its preparation method and application. The present invention forms a co-doping of metallic aluminum and lithium hydride in the silicon anode material through a specific method, which can endow the lithium-ion battery with higher first Coulombic efficiency and cycling stability.

[0005] The specific technical solution of the present invention is as follows:

[0006] In the first aspect, the present invention discloses a preparation method of an Al- and LiH-codoped silicon anode material, comprising the following steps: mixing Si and LiAlH 4After powder pressing, vacuum heat treatment is carried out at 160 - 190 °C for 3 - 6 h, and then vacuum heat treatment is carried out at 200 - 300 °C for 2 - 5 h to obtain the silicon negative electrode material co-doped with Al and LiH.

[0007] The present invention adopts a two-step vacuum heat treatment method to decompose LiAlH 4 along a specific reaction path: during the vacuum heat treatment at 160 - 190 °C, LiAlH 4 decomposes into Li 3 AlH 6 , Al and H 2 ; during the vacuum heat treatment at 200 - 300 °C, Li 3 AlH 6 further decomposes into LiH, Al and H 2 ; the thermal decomposition of LiH requires a temperature above 400 °C, so during the preparation of the negative electrode material of the present invention, LiH does not further decompose. Through the above method, nano-sized and highly dispersed and uniform metal aluminum and lithium hydride can be in-situ generated, and when doped in the silicon negative electrode material, they can play the following roles:

[0008] (1) The alloying / dealloying potentials of aluminum and silicon are similar, both being 0.3 - 0.4 V (vs Li + / Li). The in-situ generated nano-aluminum particles have high reversibility of alloying / dealloying reactions, which can improve the Coulomb efficiency and cycle capacity retention rate of charge and discharge cycles.

[0009] (2) During the charging process of the lithium-ion battery, lithium ions migrate from the positive electrode to the negative electrode and undergo alloying reactions with Si and Al in the negative electrode to form lithium-silicon alloy and lithium-aluminum alloy. The present invention adopts LiAlH 4 through a specific two-step vacuum heat treatment method, and the in-situ generated lithium hydride has the characteristics of nano-size and high dispersion uniformity. After the nucleation of the above two alloys, through the electric field effect between lithium hydride and lithium-aluminum alloy and lithium-silicon alloy, it can promote the lithium ion transport inside the negative electrode and balance the electric field on the surface of the alloy material, thus avoiding the growth of lithium dendrites induced by local potential on the material surface, and further improving the cycle stability of the lithium-ion battery. On the contrary, lithium hydride with large particle size and low dispersion uniformity will increase the local potential difference at each point on the surface of the alloy material, leading to the accelerated growth of lithium dendrites.

[0010] Preferably, the molar ratio of Si to LiAlH 4 is 2 - 8:1.

[0011] When the ratio of Si to LiAlH 4 is controlled within the above range, the battery capacity and cycle stability can be effectively improved; while when LiAlH 4When the dosage of 4 is too low, the use of LiAlH

[0012] will instead lead to a decrease in battery capacity and cycling stability.

[0013] Preferably, during the vacuum heat treatment at 160 - 190 °C and the vacuum heat treatment at 200 - 300 °C, the vacuum degree is not less than 10 kPa. 4 Preferably, before powder tabletting, Si and LiAlH

[0014] are first mixed and subjected to high - energy ball milling. 4 By subjecting Si and LiAlH

[0015] to high - energy ball milling, the particle size of the material can be refined, which helps the in - situ formed metallic aluminum and lithium hydride after vacuum heat treatment to have a smaller particle size and higher dispersion uniformity, thereby improving the first Coulombic efficiency and cycling stability of the lithium - ion battery.

[0016] Preferably, the mixing and high - energy ball milling process is carried out in an inert atmosphere.

[0017] Further, the inert atmosphere is an argon atmosphere.

[0018] Preferably, during the high - energy ball milling, the ball - to - material ratio is 60 - 120:1, the revolution speed is 200 - 500 rpm, and the time is 1 - 5 h.

[0019] Further, during the high - energy ball milling, the ball - to - material ratio is 80 - 100:1, the revolution speed is 300 - 400 rpm, and the time is 2 - 3 h.

[0020] Preferably, during the powder tabletting, the pressure is 100 - 300 MPa.

[0021] Further, during the powder tabletting, the pressure is 150 - 250 MPa.

[0022] Second, the present invention discloses an Al and LiH co - doped silicon anode material prepared by the above - mentioned preparation method.

[0023] Third, the present invention discloses the application of the Al and LiH co - doped silicon anode material in a lithium - ion battery. The lithium - ion battery includes a negative electrode; the negative electrode uses the Al and LiH co - doped silicon anode material.

[0024] Preferably, the lithium - ion battery is a solid - state lithium - ion battery.

[0025] Preferably, the lithium ion battery further includes a positive electrode; the positive electrode uses a lithium-containing positive electrode material; the lithium-containing positive electrode material includes LiNi 0.8 Co 0.1 Mn 0.1 O 2 and / or LiCoO 2 .

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

[0027] The present invention uses LiAlH 4 as a raw material. After specific two-step vacuum heat treatment, metallic aluminum and lithium hydride with nano-size and high dispersion uniformity are in-situ generated. When the obtained Al and LiH co-doped silicon negative electrode material is used in a lithium ion battery, the battery can have a high initial Coulomb efficiency and cycle stability; in addition, the Al and LiH co-doped silicon negative electrode material prepared by the method of the present invention also has a high electronic conductivity and can increase the battery capacity. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 is the change of the discharge specific capacity of the batteries prepared in Examples 1 to 3 and Comparative Examples 1 to 2 with the number of cycle turns. Figure 1 In, "Si" represents the battery prepared in Comparative Example 1, "Si-Al (18:1) " represents the battery prepared in Comparative Example 2, "Si-Al (8:1) " represents the battery prepared in Example 1, "Si-Al (4:1) " represents the battery prepared in Example 2, "Si-Al (2:1) " represents the battery prepared in Example 3.

[0029] Figure 2 is the X-ray diffraction pattern of the negative electrode materials prepared in Example 1, Example 3 and Comparative Example 2. Figure 2 In, "Si-Al (2:1) " represents the battery prepared in Example 3, "Si-Al (8:1) " represents the battery prepared in Example 1, "Si-Al (18:1) " represents the battery prepared in Comparative Example 2.

[0030] Figure 3 is the scanning electron microscope image of the negative electrode material prepared in Example 1.

[0031] Figure 4 is the electronic conductivity of the negative electrode materials prepared in Example 1 and Comparative Example 1. Figure 4 In, "Si" represents the negative electrode material prepared in Comparative Example 1, "Si-Al (8:1) " represents the negative electrode material prepared in Example 1. Detailed implementation manners

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

[0033] First, the present invention relates to a preparation method of an Al- and LiH-codoped silicon anode material, comprising the following steps: Si and LiAlH are 4 After being subjected to powder tabletting, vacuum heat treatment is carried out at 160-190 °C for 3-6 h, and then vacuum heat treatment is carried out at 200-300 °C for 2-5 h to obtain the Al- and LiH-codoped silicon anode material.

[0034] In some specific implementation manners, the molar ratio of the Si and LiAlH is 4 2-8:1.

[0035] In some specific implementation manners, before powder tabletting, the Si and LiAlH are first 4 mixed and subjected to high-energy ball milling. Among them, optionally or preferably: the process of the mixing and high-energy ball milling is carried out in an inert atmosphere, and the inert atmosphere is an argon atmosphere; the high-energy ball milling method is planetary ball milling, the ball-to-material ratio is 60-120:1, the revolution speed is 200-500 rpm, and the time is 1-5 h.

[0036] In some specific implementation manners, during the powder tabletting process, the pressure is 100-300 MPa.

[0037] In some specific implementation manners, during the vacuum heat treatment at 160-190 °C and the vacuum heat treatment at 200-300 °C, the vacuum degree is not lower than 10 kPa.

[0038] Second, the present invention relates to an Al- and LiH-codoped silicon anode material prepared by the above preparation method.

[0039] Third, the present invention relates to the application of the above Al- and LiH-codoped silicon anode material in a lithium-ion battery, and the lithium-ion battery includes a negative electrode; the negative electrode uses the Al- and LiH-codoped silicon anode material.

[0040] In some specific implementation manners, the lithium-ion battery is a solid-state lithium-ion battery.

[0041] In some specific implementation manners, the lithium-ion battery further includes a positive electrode; the positive electrode uses a lithium-containing positive electrode material; the lithium-containing positive electrode material includes LiNi 0.8 Co 0.1 Mn 0.1 O 2 and / or LiCoO 2 .

[0042] 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, the 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.

[0043] Example 1

[0044] Through the following steps, an Al and LiH co-doped silicon anode material is prepared and used in a solid-state lithium-ion battery:

[0045] S1: In an argon atmosphere, Si and LiAlH powders with a molar ratio of 8:1 are preliminarily ground in a mortar to ensure uniform mixing, obtaining a Si / LiAlH mixed powder; 4 4 mixed powder;

[0046] S2: The Si / LiAlH mixed powder is put into a stainless steel ball milling jar, sealed, and subjected to a mixing process by planetary high-energy ball milling in an argon atmosphere. The ball-to-powder ratio is set to 100:1, the revolution speed of the ball mill is set to 400 rpm, and ball milling is carried out for 2 h, obtaining a Si / LiAlH mixed ball-milled powder; 4 4 mixed ball-milled powder;

[0047] S3: The Si / LiAlH mixed ball-milled powder is pressed into a powder tablet under a pressure of 150 MPa, obtaining a Si / LiAlH mixed tablet; 4 4 mixed tablet;

[0048] S4: The Si / LiAlH mixed tablet is put into a stainless steel tube, and the stainless steel tube is evacuated by means of a vacuum diaphragm valve to ensure that the vacuum degree in the tube during subsequent heat treatment is not lower than 10 kPa. The temperature in the tube is raised to 180 °C, heat treatment is carried out at 180 °C for 3 h, then the temperature is raised to 210 °C, and heat treatment is continued at 210 °C for 5 h, and then cooled to room temperature, obtaining an Al and LiH co-doped silicon anode material, the morphology of which is as shown; 4 Figure 3 shown;

[0049] S5: Using the anode material prepared in step S4 as the anode, NCM811 / VGCF / Li 6 PS 5 Cl (mass ratio 65:5:35) as the composite cathode, and Li 6 PS 5 Cl as the solid electrolyte, a solid-state lithium-ion battery with a laminated structure is obtained by powder cold pressing.

[0050] Example 2​​​​

[0051] The Al and LiH co-doped silicon anode material is prepared through the following steps and used in a solid-state lithium-ion battery:

[0052] S1: In an argon atmosphere, Si and LiAlH powders with a molar ratio of 4:1 are preliminarily ground in a mortar to ensure uniform mixing, obtaining a Si / LiAlH mixed powder; 4 powder is preliminarily ground in a mortar to ensure uniform mixing of the two, obtaining a Si / LiAlH 4 mixed powder;

[0053] S2: The Si / LiAlH 4 mixed powder is put into a stainless-steel ball-milling jar, sealed, and subjected to a mixing process by planetary high-energy ball milling in an argon atmosphere. The ball-to-material ratio is set to 100:1, the revolution speed of the ball mill is set to 400 rpm, and ball milling is carried out for 2 h to obtain a Si / LiAlH 4 mixed ball-milled powder;

[0054] S3: The Si / LiAlH 4 mixed ball-milled powder is subjected to powder tabletting under a pressure of 150 MPa to obtain a Si / LiAlH 4 mixed tablet;

[0055] S4: The Si / LiAlH 4 mixed tablet is put into a stainless-steel tube, and the stainless-steel tube is evacuated by means of a vacuum diaphragm valve to ensure that the vacuum degree inside the tube during subsequent heat treatment is not lower than 10 kPa. The temperature inside the tube is raised to 180 °C, heat-treated at 180 °C for 3 h, then raised to 210 °C, and continued to be heat-treated at 210 °C for 5 h, and then cooled to room temperature to obtain the Al and LiH co-doped silicon anode material;

[0056] S5: Using the anode material prepared in step S4 as the anode, NCM811 / VGCF / Li 6 PS 5 Cl (mass ratio 65:5:35) as the composite cathode, and Li 6 PS 5 Cl as the solid electrolyte, a solid-state lithium-ion battery with a laminated structure is obtained by powder cold pressing.

[0057] Example 3

[0058] The Al and LiH co-doped silicon anode material is prepared through the following steps and used in a solid-state lithium-ion battery:

[0059] S1: In an argon atmosphere, Si and LiAlH powders with a molar ratio of 2:1 are preliminarily ground in a mortar to ensure uniform mixing, obtaining a Si / LiAlH 4 powder is preliminarily ground in a mortar to ensure uniform mixing of the two, obtaining a Si / LiAlH 4Mixed powder;

[0060] S2: Put the Si / LiAlH 4 mixed powder into a stainless - steel ball - milling jar, seal it, and carry out mixing treatment in an argon atmosphere by means of planetary high - energy ball milling. The ball - to - material ratio is set to 100:1, the revolution speed of the ball mill is set to 400 rpm, and ball - mill for 2 h to obtain Si / LiAlH 4 mixed ball - milled powder;

[0061] S3: Press the Si / LiAlH 4 mixed ball - milled powder at a pressure of 150 MPa to obtain Si / LiAlH 4 mixed tablet;

[0062] S4: Put the Si / LiAlH 4 mixed tablet into a stainless - steel tube, evacuate the stainless - steel tube by means of a vacuum diaphragm valve to ensure that the vacuum degree inside the tube during subsequent heat treatment is not lower than 10 kPa. Raise the temperature inside the tube to 180 °C, heat - treat at 180 °C for 3 h, then raise the temperature to 210 °C, continue to heat - treat at 210 °C for 5 h, and then cool to room temperature to obtain an Al - and - LiH - co - doped silicon anode material;

[0063] S5: Use the anode material prepared in step S4 as the anode, use NCM811 / VGCF / Li 6 PS 5 Cl (mass ratio 65:5:35) as the composite cathode, and use Li 6 PS 5 Cl as the solid - state electrolyte, and obtain a laminated - structure solid - state lithium - ion battery by means of powder cold pressing.

[0064] Example 4

[0065] Prepare an Al - and - LiH - co - doped silicon anode material through the following steps and use it in a solid - state lithium - ion battery:

[0066] S1: In an argon atmosphere, preliminarily grind the powders of Si and LiAlH with a molar ratio of 8:1 in a mortar to ensure uniform mixing, and obtain Si / LiAlH 4 mixed powder; 4 S2: Put the Si / LiAlH

[0067] mixed powder into a stainless - steel ball - milling jar, seal it, and carry out mixing treatment in an argon atmosphere by means of planetary high - energy ball milling. The ball - to - material ratio is set to 100:1, the revolution speed of the ball mill is set to 400 rpm, and ball - mill for 2 h to obtain Si / LiAlH 4 mixed ball - milled powder; 4 S3: Press the Si / LiAlH

[0068] S3: Press the Si / LiAlH 4 mixed ball-milled powder under a pressure of 150 MPa to obtain a Si / LiAlH 4 mixed tablet;

[0069] S4: Place the Si / LiAlH 4 mixed tablet into a stainless-steel tube, evacuate the stainless-steel tube by means of a vacuum diaphragm valve to ensure that the vacuum degree inside the tube during subsequent heat treatment is not lower than 10 kPa, raise the temperature inside the tube to 160 °C, after heat treatment at 160 °C for 6 h, raise the temperature to 300 °C, continue heat treatment at 300 °C for 2 h, and then cool to room temperature to obtain an Al- and LiH-codoped silicon anode material;

[0070] S5: Use the anode material prepared in step S4 as the anode, use NCM811 / VGCF / Li 6 PS 5 Cl (mass ratio 65:5:35) as the composite cathode, use Li 6 PS 5 Cl as the solid electrolyte, and obtain a solid-state lithium-ion battery with a laminated structure by means of powder cold pressing.

[0071] Example 5

[0072] Prepare an Al- and LiH-codoped silicon anode material through the following steps and use it in a solid-state lithium-ion battery:

[0073] S1: In an argon atmosphere, preliminarily grind the powders of Si and LiAlH with a molar ratio of 8:1 in a mortar to ensure uniform mixing and obtain a Si / LiAlH 4 mixed powder; 4

[0074] S2: Place the Si / LiAlH 4 mixed powder into a stainless-steel ball-milling jar, seal it, and perform a mixing process in an argon atmosphere by means of planetary high-energy ball milling. Set the ball-to-material ratio to 100:1, set the revolution speed of the ball mill to 400 rpm, and ball mill for 2 h to obtain a Si / LiAlH 4 mixed ball-milled powder;

[0075] S3: Press the Si / LiAlH 4 mixed ball-milled powder under a pressure of 150 MPa to obtain a Si / LiAlH 4 mixed tablet;

[0076] S4: Place the Si / LiAlH 4 ​The mixed tablets are placed into a stainless-steel tube, and the stainless-steel tube is evacuated by means of a vacuum diaphragm valve to ensure that the vacuum degree inside the tube during subsequent heat treatment is not lower than 10 kPa. The temperature inside the tube is raised to 190 °C, and after heat treatment at 190 °C for 3 h, the temperature is raised to 200 °C and heat treatment is continued at 200 °C for 5 h. Subsequently, it is cooled to room temperature to obtain an Al- and LiH-codoped silicon anode material;

[0077] S5: Using the anode material prepared in step S4 as the anode, using NCM811 / VGCF / Li 6 PS 5 Cl (mass ratio 65:5:35) as the composite cathode, and using Li 6 PS 5 Cl as the solid electrolyte, a solid-state lithium-ion battery with a laminated structure is obtained by means of powder cold pressing.

[0078] Comparative example 1

[0079] This comparative example uses a pure silicon anode material, using NCM811 / VGCF / Li 6 PS 5 Cl (mass ratio 65:5:35) as the composite cathode, and using Li 6 PS 5 Cl as the solid electrolyte, a solid-state lithium-ion battery with a laminated structure is obtained by means of powder cold pressing.

[0080] Comparative example 2

[0081] An Al- and LiH-codoped silicon anode material is prepared through the following steps and used in a solid-state lithium-ion battery:

[0082] S1: In an argon atmosphere, Si and LiAlH 4 powders with a molar ratio of 18:1 are preliminarily ground in a mortar to ensure uniform mixing of the two to obtain a Si / LiAlH 4 mixed powder;

[0083] S2: The Si / LiAlH 4 mixed powder is placed into a stainless-steel ball-milling jar, sealed, and subjected to a mixing process by means of planetary high-energy ball milling in an argon atmosphere. The ball-to-material ratio is set to 100:1, the revolution speed of the ball mill is set to 400 rpm, and ball milling is carried out for 2 h to obtain a Si / LiAlH 4 mixed ball-milled powder;

[0084] S3: The Si / LiAlH 4 mixed ball-milled powder is subjected to powder tabletting under a pressure of 150 MPa to obtain a Si / LiAlH 4 mixed tablet;

[0085] S4: Put the Si / LiAlH 4 mixed tablet into a stainless-steel tube, and evacuate the stainless-steel tube with the help of a vacuum diaphragm valve to ensure that the vacuum degree of the internal environment of the tube during subsequent heat treatment is not lower than 10 kPa. Raise the temperature inside the tube to 180 °C, heat-treat at 180 °C for 3 h, then raise the temperature to 210 °C, continue to heat-treat at 210 °C for 5 h, and then cool to room temperature to obtain an Al- and LiH-codoped silicon anode material;

[0086] S5: Use the anode material prepared in step S4 as the anode, use NCM811 / VGCF / Li 6 PS 5 Cl (mass ratio 65:5:35) as the composite cathode, and use Li 6 PS 5 Cl as the solid electrolyte, and obtain a solid-state lithium-ion battery with a laminated structure by powder cold pressing.

[0087] Comparative Example 3

[0088] Prepare an Al- and LiH-codoped silicon anode material through the following steps and use it in a solid-state lithium-ion battery:

[0089] S1: In an argon atmosphere, preliminarily grind the powders of Si and LiAlH 4 with a molar ratio of 8:1 in a mortar to ensure uniform mixing and obtain a Si / LiAlH 4 mixed powder;

[0090] S2: Put the Si / LiAlH 4 mixed powder into a stainless-steel ball milling tank, seal it, and perform mixing treatment by planetary high-energy ball milling in an argon atmosphere. Set the ball-to-material ratio to 100:1, set the revolution speed of the ball mill to 400 rpm, and ball mill for 2 h to obtain a Si / LiAlH 4 mixed ball-milled powder;

[0091] S3: Press the Si / LiAlH 4 mixed ball-milled powder into a powder tablet under a pressure of 150 MPa to obtain a Si / LiAlH 4 mixed tablet;

[0092] S4: Put the Si / LiAlH 4 mixed tablet into a stainless-steel tube, and evacuate the stainless-steel tube with the help of a vacuum diaphragm valve to ensure that the vacuum degree of the internal environment of the tube during subsequent heat treatment is not lower than 10 kPa. Raise the temperature inside the tube to 210 °C, heat-treat at 210 °C for 8 h, and then cool to room temperature to obtain an Al- and LiH-codoped silicon anode material;

[0093] S5: Using the negative electrode material prepared in step S4 as the negative electrode, using NCM811 / VGCF / Li 6 PS 5 Cl (mass ratio 65:5:35) as the composite positive electrode, and using Li 6 PS 5 Cl as the solid electrolyte, a solid-state lithium-ion battery with a laminated structure is obtained by powder cold pressing.

[0094] Comparative Example 4

[0095] The Al and LiH co-doped silicon negative electrode material is prepared through the following steps and used in a solid-state lithium-ion battery:

[0096] S1: In an argon atmosphere, Si and LiAlH 4 powders with a molar ratio of 8:1 are preliminarily ground in a mortar to ensure uniform mixing, obtaining a Si / LiAlH 4 mixed powder;

[0097] S2: The Si / LiAlH 4 mixed powder is put into a stainless steel ball milling tank, sealed, and subjected to mixing treatment by planetary high-energy ball milling in an argon atmosphere. The ball-to-material ratio is set to 100:1, the revolution speed of the ball mill is set to 400 rpm, and ball milling is carried out for 2 h to obtain a Si / LiAlH 4 mixed ball milled powder;

[0098] S3: The Si / LiAlH 4 mixed ball milled powder is pressed into a powder tablet under a pressure of 150 MPa to obtain a Si / LiAlH 4 mixed tablet;

[0099] S4: The Si / LiAlH 4 mixed tablet is put into a stainless steel tube, and the stainless steel tube is evacuated by means of a vacuum diaphragm valve to ensure that the vacuum degree inside the tube during subsequent heat treatment is not lower than 10 kPa. The temperature inside the tube is raised to 180 °C, heat treated at 180 °C for 3 h, then raised to 450 °C, and continued to be heat treated at 450 °C for 5 h, and then cooled to room temperature to obtain the Al and LiH co-doped silicon negative electrode material;

[0100] S5: Using the negative electrode material prepared in step S4 as the negative electrode, using a mixture of NCM811 / VGCF / Li 6 PS 5 Cl (mass ratio 65:5:35) as the composite positive electrode, and using Li 6 PS 5 Cl as the solid electrolyte, a solid-state lithium-ion battery with a laminated structure is obtained by powder cold pressing.

[0101] Comparative Example 5

[0102] The Al and LiH co-doped silicon anode material was prepared through the following steps and used in a solid-state lithium-ion battery:

[0103] S1: In an argon atmosphere, the powders of Si, Al, and LiH with a molar ratio of 8:1:1 were preliminarily ground in a mortar to ensure uniform mixing of the three, obtaining a Si / Al / LiH mixed powder;

[0104] S2: The Si / Al / LiH mixed powder was put into a stainless-steel ball-milling jar, sealed, and subjected to a mixing process by planetary high-energy ball milling in an argon atmosphere. The ball-to-material ratio was set to 100:1, the revolution speed of the ball mill was set to 400 rpm, and ball milling was carried out for 2 h to obtain a Si / Al / LiH mixed ball-milled powder;

[0105] S3: The Si / Al / LiH mixed ball-milled powder was subjected to powder tabletting under a pressure of 150 MPa to obtain a Si / Al / LiH mixed tablet;

[0106] S4: The Si / Al / LiH mixed tablet was put into a stainless-steel tube, and the stainless-steel tube was evacuated by means of a vacuum diaphragm valve to ensure that the vacuum degree in the tube during subsequent heat treatment was not lower than 10 kPa. The temperature in the tube was raised to 180 °C, heat treatment was carried out at 180 °C for 3 h, then the temperature was raised to 210 °C, and heat treatment was continued at 210 °C for 5 h, and then cooled to room temperature to obtain the Al and LiH co-doped silicon anode material;

[0107] S5: Using the anode material prepared in step S4 as the anode, using NCM811 / VGCF / Li 6 PS 5 Cl mixture (mass ratio of 65:5:35) as the composite cathode, and using Li 6 PS 5 Cl as the solid electrolyte, a solid-state lithium-ion battery with a laminated structure was obtained by means of powder cold pressing.

[0108] Test Example 1: Doping of Al and LiH

[0109] The anode materials prepared in Example 1, Example 3, and Comparative Example 2 were taken, and the X-ray diffraction (XRD) patterns were detected. The results are shown in Figure 2 . From Figure 2 it can be seen that: when the molar ratio of Si and LiAlH 4 is 2:1, obvious characteristic peaks of Al and LiH appear in the XRD pattern (due to the similarity of crystal structures, the characteristic peaks of Al and LiH basically coincide); when the molar ratio of Si and LiAlH 4When the molar ratios are 8:1 and 18:1, due to the low contents of Al and LiH and small crystal grains, the detection limits of the XRD patterns are not reached, so no obvious characteristic peaks of Al and LiH are shown.

[0110] Test Example 2: Battery Performance

[0111] The cycle performance tests were carried out on the batteries prepared in each example and comparative example under the following test conditions: the temperature was 60 °C, the charge-discharge current was 0.1C, and the pressure was 50 MPa. The first discharge specific capacity, the first Coulombic efficiency, and the capacity retention rate after 20 cycles are shown in Table 1; under different Si and LiAlH 4 mixing ratios, the change in the discharge specific capacity during the 1st to 20th cycles is shown in Figure 1 .

[0112] Table 1 Detection Results of Battery Performance

[0113]

[0114] From Table 1 and Figure 1 it can be seen that:

[0115] (1) The detection results of Examples 1 to 5 and Comparative Example 1 show that compared with the pure silicon anode material, after introducing metal aluminum and lithium hydride doping by the method of the present invention, the capacity, the first Coulombic efficiency, and the cycle stability of the battery can be effectively improved. The reason for the analysis is as follows: by using the method of the present invention, metal aluminum and lithium hydride with nano-size and high dispersion uniformity can be in-situ generated. Among them, metal aluminum has a high reversibility of alloying / dealloying reactions, and lithium hydride with the above characteristics can generate an electric field effect with the lithium-aluminum alloy and lithium-silicon alloy formed during the battery charging process, promote the lithium ion transport inside 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.

[0116] (2) The detection results of Examples 1 to 3 and Comparative Examples 1 to 2 show that during the preparation of the anode material, when the molar ratio of Si and LiAlH 4 is 2 to 8:1, compared with the pure silicon anode material, the capacity, the first Coulombic efficiency, and the cycle stability of the battery can be effectively improved. When the dosage of LiAlH 4 is too small (Comparative Example 2), both the capacity and the cycle stability of the battery are reduced compared with the pure silicon anode material.

[0117] (3) The detection results of Example 1 and Comparative Example 3 show that compared with the method of using one-step vacuum heat treatment to make LiAlH 4In terms of decomposition into LiH and Al, adopting the two-step vacuum heat treatment method in the present invention can improve the cycle stability of the battery. The reason is as follows: When adopting the one-step vacuum heat treatment method, the generated lithium hydride has a large size and poor dispersion uniformity, which will increase the local potential difference at each point on the surface of the alloy material, leading to the accelerated growth of lithium dendrites. For the same reason, in Comparative Example 5, directly using LiH and Al to form doping in the silicon negative electrode material results in a lower cycle stability of the battery than that in Example 1.

[0118] (4)The test results of Example 1 and Comparative Example 4 show that during the preparation of the silicon negative electrode material co-doped with Al and LiH, when the temperature of the vacuum heat treatment is too high, the cycle stability of the battery will decrease. The reason is as follows: When the temperature of the vacuum heat treatment is too high, LiH will decompose, and it is difficult to utilize the electric field effect between lithium hydride, lithium-aluminum alloy, and lithium-silicon alloy to better promote the lithium ion transport inside the negative electrode and balance the electric field on the surface of the alloy material, so the effect of improving the cycle stability of the battery is poor.

[0119] Test Example 3: Electronic conductivity of the negative electrode material

[0120] Take the negative materials prepared in Example 1 and Comparative Example 1 for electronic conductivity detection. The detection conditions are as follows: the temperature is 25 °C and the voltage is 10 mV. The measured current-time curve is shown in Figure 4 . From Figure 4 it can be seen that: compared with the pure silicon negative electrode material, after doping with metal aluminum and lithium hydride by the method of the present invention, the electronic conductivity of the silicon negative electrode material can be effectively improved.

[0121] Unless otherwise defined, all technical terms and scientific terms used in the present invention have the same meaning as commonly understood by those of ordinary skill in the art to which the present disclosure belongs. The raw materials and equipment used in the present invention are conventional raw materials and equipment in the art and can be obtained from conventional commercial channels without special instructions; the methods used in the present invention are 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 fall within the protection scope of the technical solution of the present invention.

Claims

1. A method for preparing an Al and LiH co-doped silicon negative electrode material, characterized in that: The method comprises the following steps: mixing Si and LiAlH4, high-energy ball milling for 1 to 5 hours at a ball-to-material ratio of 60 to 120:1 and a revolution speed of 200 to 500 rpm, tableting the powder, vacuum heat treatment at 160 to 190°C for 3 to 6 hours, and vacuum heat treatment at 200 to 300°C for 2 to 5 hours to obtain Al and LiH co-doped silicon negative electrode material.

2. The preparation method according to claim 1, characterized in that: During the vacuum heat treatment at 160-190° C., the vacuum degree is not less than 10 kPa.

3. The preparation method according to claim 1, characterized in that: During the vacuum heat treatment at 200-300° C., the vacuum degree is not less than 10 kPa.

4. The preparation method according to claim 1, characterized in that: The mixing process is carried out in an inert atmosphere.

5. The preparation method according to claim 1, characterized in that: The high energy ball milling process is carried out in an inert atmosphere.

6. The preparation method according to claim 1, characterized in that: The high energy ball milling method is planetary ball milling.

7. The preparation method according to claim 1, characterized in that: During the powder tableting process, the pressure is 100-300 MPa.

8. An Al and LiH co-doped silicon negative electrode material prepared by the preparation method according to any one of claims 1 to 7.

9. The use of the Al and LiH co-doped silicon negative electrode material in a lithium ion battery according to claim 8, characterized in that: The lithium-ion battery comprises a negative electrode; the negative electrode adopts the Al and LiH co-doped silicon negative electrode material.

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