Porous silicon-silver-lithium composite negative electrode material and preparation method thereof, and all-solid-state battery

Abstract

This invention provides a porous silicon-silver-lithium composite anode material and its preparation method, as well as an all-solid-state battery, relating to the field of all-solid-state battery materials. The porous silicon-silver-lithium composite anode material comprises porous silicon, silver, a lithium-silicon alloy, and a sulfide, wherein the lithium-silicon alloy is Li... 14 Si6. The porous silicon-silver-lithium composite anode material exhibits minimal volume change and good structural stability during battery charge and discharge. It maintains close adhesion to the electrolyte layer, with a stable and effective interface, thereby improving the battery's cycle performance. Additionally, lithium-silicon alloys (Li...) 14 Si6 supplements the lithium source of the battery and improves the battery's coulombic efficiency.

Description

Technical Field

[0001] This invention relates to the field of all-solid-state battery materials, specifically to a porous silicon-silver-lithium composite anode material and its preparation method, and an all-solid-state battery. Background Technology

[0002] Sulfide-based all-solid-state batteries are one of the technological development directions of the lithium battery industry at home and abroad. The high energy density of all-solid-state batteries requires the use of positive and negative electrode materials with high specific capacity. Silicon, as the basic material of lithium battery negative electrode, has the advantages of high specific capacity, abundant resources and low cost.

[0003] However, the volume change of silicon crystals of more than 300% during the intrinsic lithium insertion and delithiation process in both liquid lithium batteries and all-solid-state lithium batteries affects their practical use in batteries. In particular, the volume expansion and contraction of silicon anode sheets in all-solid-state batteries leads to easy cracking and failure of the solid electrolyte interface, resulting in poor battery cycle stability. At the same time, silicon anodes also have defects such as low initial coulombic efficiency. Summary of the Invention

[0004] (a) Technical problems to be solved

[0005] To address the shortcomings of existing technologies, this invention provides a porous silicon-silver-lithium composite anode material and its preparation method, as well as an all-solid-state battery. This invention solves the defects of all-solid-state batteries, such as easy cracking and failure of the solid electrolyte interface due to volume expansion and contraction of the silicon anode sheet, and low initial coulombic efficiency.

[0006] (II) Technical Solution

[0007] To achieve the above objectives, the present invention provides the following technical solution:

[0008] In a first aspect, this application discloses a porous silicon-silver-lithium composite anode material, which comprises porous silicon, silver, a lithium-silicon alloy, and a sulfide; the lithium-silicon alloy is Li 14 Si6.

[0009] Secondly, this application discloses a method for preparing the porous silicon-silver-lithium composite anode material, comprising the following steps: providing a silver-containing substance and a silicon-containing substance to prepare silver-containing porous silicon; the silver-containing porous silicon undergoes a pre-lithiation process to prepare partially pre-lithiated porous silicon-silver; the partially pre-lithiated porous silicon-silver is composited with a sulfide and then mixed with a film-forming agent to prepare the porous silicon-silver-lithium composite anode material.

[0010] Thirdly, this application discloses an all-solid-state battery, which includes the aforementioned porous silicon-silver-lithium composite anode material, solid electrolyte, and cathode material.

[0011] (III) Beneficial Effects

[0012] This invention provides a porous silicon-silver-lithium composite anode material. Compared with the prior art, it has the following advantages:

[0013] This application presents a porous silicon-silver-lithium composite anode material comprising porous silicon, silver, and a lithium-silicon alloy (Li). 14 A porous silicon-silver-lithium composite anode material is prepared by partially pre-lithiation of the silver-containing porous silicon and lithium-containing materials with Si6 and sulfides at a lithium-to-silicon molar ratio of 1.3-1.7:1. This porous silicon-silver-lithium composite anode material exhibits minimal volume change and good structural stability during battery charge and discharge. It maintains close adhesion to the electrolyte layer, and the bonding interface is stable and effective, thereby improving the battery's cycle performance. Additionally, lithium-silicon alloy Li... 14 Si6 supplements the lithium source of the battery and improves the battery's coulombic efficiency. Attached Figure Description

[0014] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0015] Figure 1 The image shows the SEM analysis of porous silica powder A containing nano-silver particles in Example 1.

[0016] Figure 2 The XRD pattern of porous silica powder A containing nano-silver particles in Example 1 is shown below.

[0017] Figure 3 This is the XRD pattern of partially pre-lithiated porous silicon silver B from Example 1;

[0018] Figure 4 The cross-sectional scanning electron microscope and EDS analysis spectrum of the negative electrode sheet after the battery prepared by the porous silicon-silver-lithium composite negative electrode material of Example 1 has been stably cycled for more than 500 cycles under 1C conditions.

[0019] Figure 5 The XRD pattern of the porous silicon-silver-lithium composite anode material in Comparative Example 1 is shown.

[0020] Figure 6 Scanning electron microscopy (SEM) and EDS analysis images of the composite anode material prepared in Comparative Example 5;

[0021] Figure 7 EDS of porous silica powder A in Example 1. Detailed Implementation

[0022] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention are described clearly and completely. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0023] The first aspect of this application discloses a porous silicon-silver-lithium composite anode material, which comprises porous silicon, silver, a lithium-silicon alloy, and a sulfide; the lithium-silicon alloy is Li. 14 Si6. A porous silicon-silver-lithium composite anode material is prepared by providing the silver-containing porous silicon and lithium-containing material at a lithium-to-silicon molar ratio of 1.3-1.7:1. This porous silicon-silver-lithium composite anode material exhibits minimal volume change and good structural stability during battery charge-discharge processes. It maintains close adhesion to the electrolyte layer, and the bonding interface is stable and effective, thereby improving the battery's cycle performance. Additionally, the lithium-silicon alloy Li... 14 Si6 supplements the lithium source of the battery and improves the battery's coulombic efficiency.

[0024] In some examples, the porous silicon has a pore size of 20-25 nm. For example, the pore size of the porous silicon can be any value among 20 nm, 23 nm, and 25 nm, or any value between two of them, and the specific surface area is 25-30 m². 2 / g, for example, the specific surface area can be 25 m² 2 / g、28 m 2 / g、30 m 2 Any value in / g or any value between the two.

[0025] In some examples, the sulfide is selected from lithium thiophosphate and lithium thiophosphate chloride, but is not limited thereto.

[0026] The second aspect of this application discloses a method for preparing the porous silicon-silver-lithium composite anode material, comprising the following steps:

[0027] Silver-containing porous silicon is prepared by providing silver-containing and silicon-containing materials. The silver-containing porous silicon is then subjected to a pre-lithiation process to prepare partially pre-lithiated porous silicon-silver. The partially pre-lithiated porous silicon-silver is then compounded with sulfides and mixed with a film-forming agent to prepare a porous silicon-silver-lithium composite anode material.

[0028] The preparation method of this application prepares partially pre-lithiated porous silicon silver by pre-lithiation process of silver-containing porous silicon. Partial pre-lithiation not only solves the volume change of some silicon during charge and discharge process, but also improves the coulombic efficiency of the battery and ensures the cycle stability of the assembled full battery.

[0029] As an example, the silver-containing substance is selected from silver nitrate, but is not limited thereto.

[0030] As an example, the silicon-containing material is selected from silicon powder, but is not limited thereto. Preferably, the silicon powder is micron-sized silicon powder with a particle size of 3-10 μm.

[0031] As a preferred technical solution, the pre-lithiation process includes providing the silver-containing porous silicon and lithium-containing material at a lithium to silicon molar ratio of 1.3-1.7:1, and heating the mixture at 300℃-400℃ for 20-40 minutes under an inert atmosphere. For example, the lithium to silicon molar ratio can be any value from 1.3:1, 1.5:1, 1.7:1, or any value between two of these. Partial pre-lithiation is performed by providing the silver-containing porous silicon and lithium-containing material at a lithium to silicon molar ratio of 1.3-1.7:1, resulting in a lithium-silicon alloy of Li. 14 Si6 enables the porous silicon-silver-lithium composite anode material to exhibit minimal volume change and good structural stability during battery charging and discharging. It maintains a tight bond with the electrolyte layer, and the bonding interface is stable and effective, thereby improving the battery's cycle performance.

[0032] As a preferred technical solution, the mass ratio of the partially pre-lithiated porous silicon silver to the sulfide is 3-5:1.

[0033] As an example, the film-forming agent is selected from polytetrafluoroethylene;

[0034] As a preferred technical solution, the film-forming agent further includes PAA and CMC.

[0035] The present invention also discloses an all-solid-state battery, which includes the aforementioned porous silicon-silver-lithium composite anode material, solid electrolyte, and cathode material.

[0036] I. Preparation Method

[0037] Example 1

[0038] This embodiment provides a method for preparing a composite negative electrode material, including the following steps:

[0039] Step 1: According to the designed silver content, select silver nitrate as the silver source, add silver nitrate to hydrofluoric acid solution, where the concentration of hydrofluoric acid is 3 mol / L and the concentration of silver nitrate is controlled at 6 mmol / L, stir to dissolve and form a homogeneous solution.

[0040] Step 2: Select silicon powder with a particle size of about 15 micrometers (Maclean, CAS No.: 7440-21-3). Add silicon powder to the solution obtained in Step 1 at a mass ratio of silicon powder to solution volume of 2.8:50 (g / mL). Then add hydrogen peroxide with a mass concentration of 30% (g / mL). The mass ratio of hydrogen peroxide (based on pure H2O2) to the volume ratio of the solution obtained in Step 1 is 1:50 (g / mL). Stir until the reaction is uniform. The reaction time is 12 hours.

[0041] Step 3: Filter the solution from Step 2, wash it three times with deionized water, and then filter again. Dry the obtained powder under vacuum at 80°C for 24 hours to obtain porous silicon powder A containing nano-silver particles. The pore size of porous silicon powder A is 20 nm, and the specific surface area is 25 m². 2 / g; The silver-silicon mass ratio in porous silica powder A was analyzed by EDS, and the results are shown in the figure. Figure 7 ,Depend on Figure 7 The silicon content was calculated and is shown in Table 1.

[0042] Step 4: Mix silver-containing porous silicon powder A with metallic lithium at a lithium to silicon molar ratio of 1.5:1, and heat the mixture at 350°C under an inert atmosphere for 30 minutes to obtain partially pre-lithiated porous silicon silver B.

[0043] Step 5: Mix a portion of pre-lithiated porous silicon silver B with Li3PS4 electrolyte powder at a mass ratio of 4:1 and ball mill at 500 r / min for 1 hour to obtain porous silicon composite powder C.

[0044] Step 6: Mix porous silicon composite powder C and PTFE at a mass ratio of 98:2 and ball mill at 300 r / min for 30 min to form fibers. Then roll the mixture into a film to dry prepare porous silicon silver lithium composite anode material D with a thickness of 35 μm.

[0045] Table 1

[0046]

[0047] Figure 1 The image shown is a SEM image of porous silica powder A containing silver nanoparticles from Example 1. Figure 1 It can be observed that the smooth surface of the original silicon powder is etched with a large number of nanoscale pores.

[0048] Figure 2 The XRD pattern of porous silica powder A containing silver nanoparticles in Example 1 is shown below. Figure 2 It can be determined that not only silicon crystal peaks but also silver crystal peaks are present in A, indicating that porous silicon powder A is composed of silver-containing crystalline silicon powder.

[0049] Figure 3This is the XRD pattern of partially pre-lithiated porous silicon silver B from Example 1, by... Figure 3 This indicates that the pre-lithiated porous silicon silver B contains Li. 14 The Si6 compound indicates that the reaction produced a lithium-silicon alloy, Li. 14 Si6. Since the XRD pattern shows virtually no lithium peaks, it indicates that lithium was completely reacted with silicon. The Li content was calculated by adding lithium to silicon in molar ratio. 14 The Si6 content. For example, if the molar ratio of Li:Si = 1:1, then Li3 will be formed. 14 The molar ratio of Si6 to Li is 14 Si6:Si = 1:8. Calculations show that in the partially pre-lithiated porous silicon-silver alloy of Example 1, the lithium-silicon alloy Li... 14 The molar ratio of Si6 to Si is 3:10.

[0050] Figure 4 The cross-sectional scanning electron microscope (SEM) and EDS analysis spectra of the negative electrode sheet after the battery prepared by the porous silicon-silver-lithium composite negative electrode material in Example 1 has been stably cycled for more than 500 cycles under 1C conditions are observed. Figure 4 It can be seen that silver particles are present on the surface of silicon, and the overall structure of silicon has not been broken or pulverized.

[0051] Example 2

[0052] The difference between this embodiment and embodiment 1 is that in step 4, the amount of lithium metal and the amount of silver-containing porous silicon powder A are prepared according to the lithium-silicon molar ratio of 1.3:1. The rest is the same as in embodiment 1.

[0053] Example 3

[0054] The difference between this embodiment and embodiment 1 is that in step 4, the amount of lithium metal and the amount of silver-containing porous silicon powder A are prepared according to the lithium-silicon molar ratio of 1.4:1. The rest is the same as in embodiment 1.

[0055] Example 4

[0056] The difference between this embodiment and embodiment 1 is that in step 4, the amount of lithium metal and the amount of silver-containing porous silicon powder A are prepared according to the lithium-silicon element molar ratio of 1.6:1. The rest is the same as in embodiment 1.

[0057] Example 5

[0058] The difference between this embodiment and embodiment 1 is that in step 4, the amount of lithium metal and the amount of silver-containing porous silicon powder A are prepared according to the lithium-silicon molar ratio of 1.7:1. The rest is the same as in embodiment 1.

[0059] Comparative Example 1

[0060] The difference between this comparative example and Example 1 is that in step 4, the amount of lithium metal and the amount of silver-containing porous silicon powder A are prepared according to the lithium-silicon element molar ratio of 2.0:1. The rest is the same as in Example 1.

[0061] Figure 5 The XRD pattern of the porous silicon-silver-lithium composite anode material in Comparative Example 1 is shown. Figure 5 The partial pre-lithiationd porous silicon-silver shown in Comparative Example 1 contains Li. 14 Si6 compounds, Li 14 The diffraction peaks of the Si6 compound were enhanced compared to those of Example 1, indicating that increasing the lithium to silicon ratio to 2:1 improved the Li... 14 The content of Si6 increased.

[0062] Comparative Example 2

[0063] The difference between this comparative example and Example 1 is that in step 4, the amount of lithium metal and the amount of silver-containing porous silicon powder A are prepared according to the lithium-silicon molar ratio of 1.0:1. The rest is the same as in Example 1.

[0064] Comparative Example 3

[0065] The difference between this comparative example and Example 1 is that in step 4, the amount of lithium metal and the amount of silver-containing porous silicon powder A are prepared according to the lithium-silicon element molar ratio of 3.3:1. The rest is the same as in Example 1.

[0066] Comparative Example 4

[0067] The difference between this comparative example and Example 1 is that step 4 is omitted. Instead of step 5, porous silicon powder A containing nano-silver particles (from step 3) is used to replace part of the pre-lithiated porous silicon silver B. This powder is then mixed with Li3PS4 electrolyte powder at a mass ratio of 4:1 and ball-milled at 500 r / min for 1 hour to obtain porous silicon composite powder C. All other steps are the same as in Example 1.

[0068] Comparative Example 5

[0069] The difference between this comparative example and Example 1 is that silver nitrate is used in excess. Specifically, silver nitrate is selected as the silver source, and it is added to a hydrofluoric acid solution with a concentration of 3 mol / L and a silver nitrate concentration controlled at 10 mmol / L. After stirring and dissolving, a homogeneous solution is formed. Everything else is the same as in Example 1.

[0070] Figure 6 Scanning electron microscopy (SEM) and EDS analysis images of the composite anode material prepared in Comparative Example 5 are shown. Figure 6 The composite anode material prepared with excess silver nitrate produces large-volume free silver particles.

[0071] II. Performance Testing

[0072] The porous silicon-silver-lithium composite anode material prepared in the examples and comparative examples was combined with lithium-phosphorus-sulfur-chlorine solid electrolyte powder sheets and ternary cathode sheets (NCM721) to form an all-solid-state mold battery. The battery maintained an operating pressure of 100 MPa and achieved stable cycling for more than 500 cycles at 1C. The coulombic efficiency of the first cycle, the specific capacity after 200 cycles, and the capacity retention rate after 500 cycles were tested. The test results are shown in Table 2.

[0073] Table 2 Test Results

[0074]

[0075] Table 2, comparing Examples 1-5 and Comparative Examples 1-2, shows that using a Li:Si molar ratio of 1.3-1.7:1 to partially pre-lithiate porous silicon-silver-lithium composite anode material prepared from porous silicon powder containing nano-silver particles, resulted in the formation of a lithium-silicon alloy Li during the partial pre-lithiation process. 14 Si6 is used to make the porous silicon-silver-lithium composite anode material exhibit minimal volume change and good structural stability during battery charge and discharge. It maintains a tight bond with the electrolyte layer, and the interface is stable and effective, thereby improving the battery's cycle performance. The porous silicon-silver-lithium composite anode material prepared through this pre-lithiation process supplements the battery's lithium source and improves the battery's coulombic efficiency.

[0076] Table 2, comparing Example 1 and Comparative Example 3, shows that the lithium-silicon alloy generated after partial pre-lithiation treatment is Li 22 Si5 is a lithium-rich alloy, which makes it difficult for lithium ions to insert and extract, resulting in a lower coulombic efficiency of the battery.

[0077] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0078] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

[0079] The present invention has been illustrated with the above embodiments to describe the detailed process flow of the present invention. However, the present invention is not limited to the above detailed process flow, that is, it does not mean that the present invention must rely on the above detailed process flow to be implemented. Those skilled in the art should understand that any improvements to the present invention, equivalent substitutions of the raw materials of the product of the present invention, addition of auxiliary components, selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. A porous silicon-silver-lithium composite anode material, characterized in that, The porous silicon-silver-lithium composite anode material includes porous silicon, silver, lithium-silicon alloy, and sulfides. The lithium-silicon alloy is Li 14 Si6.

2. The porous silicon-silver-lithium composite anode material as described in claim 1, characterized in that, The porous silicon has a pore size of 20-25 nm and a specific surface area of ​​25-30 m². 2 / g.

3. The porous silicon-silver-lithium composite anode material as described in claim 1, characterized in that, The sulfide is selected from lithium thiophosphate and lithium thiophosphate chloride.

4. A method for preparing a porous silicon-silver-lithium composite anode material as described in any one of claims 1-3, characterized in that, Includes the following steps: Silver-containing porous silicon is prepared by providing silver-containing and silicon-containing materials. The silver-containing porous silicon is then subjected to a pre-lithiation process to prepare partially pre-lithiated porous silicon-silver. The partially pre-lithiated porous silicon-silver is then compounded with sulfides and mixed with a film-forming agent to prepare a porous silicon-silver-lithium composite anode material.

5. The preparation method according to claim 4, characterized in that, The silver-containing substance is selected from silver nitrate.

6. The preparation method according to claim 4, characterized in that, The silicon-containing material is selected from silicon powder, which is micron-sized silicon powder with a particle size of 3-10 μm.

7. The preparation method according to claim 4, characterized in that, The pre-lithiation process includes providing the silver-containing porous silicon and the lithium-containing material at a lithium to silicon molar ratio of 1.3-1.7:1, and heating the mixture at 300℃-400℃ for 20-40 minutes under an inert atmosphere.

8. The preparation method according to claim 4, characterized in that, The mass ratio of the pre-lithiated porous silicon silver to the sulfide is 3-5:

1.

9. The preparation method according to claim 4, characterized in that, The film-forming agent is selected from polytetrafluoroethylene; Preferably, the film-forming agent further includes PAA and CMC.

10. An all-solid-state battery, characterized in that, The all-solid-state battery includes the porous silicon-silver-lithium composite anode material, solid electrolyte, and cathode material as described in any one of claims 1-3.

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