Preparation method of pSi@CaO composite material and application thereof to negative electrode of lithium ion battery

Abstract

The application belongs to the technical field of lithium ion batteries, and discloses a preparation method of a pSi@CaO composite material and application of the composite material in a negative electrode of a lithium ion battery, the preparation method of the composite material comprising the following steps: S1: subjecting SiO powder to disproportionation heat treatment; S2: etching the obtained powder with HF, then separating and drying to obtain pSi; S3: uniformly mixing the pSi with CaO, and performing coating heat treatment, so that the pSi@CaO composite material is obtained. The application improves the composition of the coating layer of porous silicon and the synthesis process, prepares porous silicon first, then coats calcium silicate on the surface of the porous silicon in situ through a reaction at high temperature, and utilizes the combination of CaO and porous silicon to form a calcium silicate coating layer, so that the method is convenient, and the obtained pSi@CaO composite material can effectively improve the first coulomb efficiency, cycle performance and rate performance of the porous silicon negative electrode.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of lithium ion batteries, and more particularly relates to a preparation method of a pSi@CaO composite material and its application in a lithium ion battery negative electrode. The pSi@CaO composite material is a composite material formed by coating porous silicon (pSi) with calcium silicate (such as CaSiO3, Ca3(Si3O9)). It can be used as a lithium ion battery negative electrode material. BACKGROUND

[0002] As one of the most successful energy storage devices, lithium ion batteries drive the development of a decarbonized society and renewable energy transformation, and are widely used in portable electronic products, energy storage devices, new energy vehicles, and other fields.

[0003] Graphite is currently the main negative electrode material for commercial lithium ion batteries, and its theoretical specific capacity is relatively low (~372 mAh g -1 ). It cannot meet the energy density requirements of the next generation of high-specific-capacity lithium ion batteries. Compared with graphite, silicon has a theoretical specific capacity of 3579 mAh g 15 Si4) at room temperature (Li -1 ), which is one of the most promising negative electrode candidates for the next generation. However, during battery charging and discharging, the alloying mechanism of Si can cause the electrode to expand in volume, resulting in the pulverization of active material particles and poor contact with the current collector. The highly reactive surface of Si is repeatedly exposed to the electrolyte, repeatedly forming a solid electrolyte interface (SEI) and continuously losing active lithium, which macroscopically manifests as a sharp decline in both battery capacity and kinetic performance.

[0004] To solve the problem of volume expansion of silicon negative electrodes, the commonly used method is to use silicon negative electrodes with a porous structure. However, the large specific surface area of the porous structure can lead to more side reactions, thereby reducing the coulombic efficiency of Si. To reduce the direct contact between the silicon negative electrode and the electrolyte, porous silicon is often in-situ compounded with carbon and other materials. Sujong Chae et al. impregnated petroleum pitch inside porous silicon, thereby obtaining a micron-sized Si / C composite material (Advanced Materials, 2021, 33(40): e2103095). Shixiong Mei et al. prepared a silicon nitride-coated porous silicon (Journal of Energy Chemistry, 2022, 69: 616-625). The above-mentioned coating layers can improve the stability of the porous silicon negative electrode to some extent, but their synthesis process needs to be simplified. Patent CN112331854A discloses a lithium magnesium silicate pre-lithiated silicon monoxide negative electrode material, a preparation method and use thereof. Silicon monoxide, lithium oxide, and magnesium oxide are uniformly mixed and then heat-treated to form a SiO / Si / Li x Mgy O z Si n Composite, and then coated with soft carbon, effectively improving the initial efficiency of the silicon monoxide negative electrode, but the heat treatment temperature is as high as 1200℃, causing the silicon grains to uncontrollably grow, affecting the cycle performance of the material. Patent CN114373915A uses hard carbon coated silicon monoxide and magnesium metal to fully mix and heat dope in an inert atmosphere, and finally coats soft carbon to obtain a composite material containing Si / Mg2SiO4 / MgO, which not only improves the initial efficiency, but also has excellent 50 cycle capacity retention rate, but the cycle current density is only 100mA / g, and the long cycle performance of the sample under large current is not mentioned. Moreover, the thermal doping of magnesium metal is an exothermic reaction, and magnesium metal itself is chemically active, which is not conducive to large-scale industrial production. The preparation of the above patents involves complex process, long preparation period, and the improvement effect on long cycle performance is not significant, so it is urgent to explore new methods to improve the stability of the silicon surface. SUMMARY

[0005] In view of the above defects or improvement needs of the prior art, the purpose of the present application is to provide a preparation method of pSi@CaO composite material and its application in lithium ion battery negative electrode, wherein the composition of the coating layer of porous silicon and the synthesis process are improved, porous silicon is first prepared, and then calcium silicate is coated on the surface of porous silicon in situ through reaction at high temperature. The method is convenient, and the pSi@CaO composite material obtained can effectively improve the initial coulomb efficiency, cycle performance and rate performance of the porous silicon negative electrode.

[0006] To achieve the above purpose, according to one aspect of the present application, a preparation method of pSi@CaO composite material is provided, characterized in that it comprises the following steps:

[0007] S1: subjecting SiO powder to disproportionation heat treatment under a protective atmosphere;

[0008] S2: etching the powder obtained in step S1 with HF to etch SiO2 in the powder and form a porous structure, and then separating the powder from HF after the reaction and drying, to obtain porous silicon powder pSi;

[0009] S3: mixing the porous silicon powder obtained in S2 with CaO uniformly and performing coating heat treatment in an inert atmosphere to obtain pSi@CaO composite material.

[0010] As a further preferred embodiment of the present application, in step S1, the reaction temperature of the disproportionation heat treatment is 850-1000℃, and the reaction time is 1-5 hours;

[0011] Preferably, the disproportionation heat treatment is carried out at 950℃ for 2 hours.

[0012] As a further preferred embodiment of the present invention, the etching in step S2 specifically involves dispersing the powder obtained in step S1 in a mixed solvent of deionized water and anhydrous ethanol, and adding HF.

[0013] Preferably, each 4.8 g of powder obtained in step S1 is dispersed in a mixed solvent of 200 mL of deionized water and 100 mL of anhydrous ethanol, and the corresponding added HF is 10-60 mL of HF solution with a mass fraction of 40%; more preferably, the corresponding added HF is 19.2 mL of HF solution with a mass fraction of 40%.

[0014] As a further preferred embodiment of the present invention, in step S3, the mass percentage of CaO in the mixture obtained by mixing porous silicon powder and CaO is 5% to 30%, more preferably 20%.

[0015] As a further preferred embodiment of the present invention, in step S3, the reaction temperature of the coating heat treatment is 900-1100℃, and the reaction time is 1-5 hours;

[0016] Preferably, the coating heat treatment is performed by holding at 1000°C for 2 hours.

[0017] As a further preferred embodiment of the present invention, in step S1, the protective atmosphere is Ar or N2.

[0018] As a further preferred embodiment of the present invention, in step S2, the separation of powder from HF is specifically performed by centrifugal separation, and the drying is specifically performed by vacuum drying.

[0019] According to another aspect of the present invention, the present invention provides a pSi@CaO composite material obtained by the above preparation method.

[0020] According to another aspect of the present invention, the present invention provides the application of the above-mentioned pSi@CaO composite material in the negative electrode of a lithium-ion battery.

[0021] Compared with existing technologies, the above-described technical solution of this invention, which involves coating porous silicon with CaO and then heat-treating them to achieve a composite material, yields calcium silicate-coated porous silicon material (pSi@CaO). This method has promising applications in improving the initial efficiency and cycle performance of porous silicon, and is also convenient. This invention first utilizes the disproportionation reaction of SiO and further etching SiO2 with HF to prepare porous silicon. Then, calcium silicate is in-situ coated onto the porous silicon surface through a high-temperature reaction (e.g., CaO + SiO2 = CaSiO3) to prepare the pSi@CaO composite material. The resulting pSi@CaO composite material is particularly suitable for use as a negative electrode material in lithium-ion batteries.

[0022] This invention, in particular, optimizes the amount of HF used in the etching reaction, controlling the amount of HF (AR, 40%) corresponding to each 4.8 g SiO sample disproportionation product to 10-60 mL. This effectively etches away most of the SiO2 in the disproportionation product, resulting in micron-sized porous silicon (the pores are mesoporous). Although HF can remove most of the SiO2 in the SiO sample disproportionation product, preventing the formation of irreversible products between SiO2 and Li during the first lithiation and thus reducing the first-cycle coulombic efficiency, pSi has a large specific surface area and is prone to numerous side reactions with the electrolyte, which also leads to low first-cycle coulombic efficiency. This invention addresses this by generating a calcium silicate coating layer (e.g., CaSiO3, Ca3(Si3O9)) on the pSi surface. This passivates SiO2, preventing irreversible reactions between Li and SiO2 during the first lithiation and improving the first-cycle coulombic efficiency. Furthermore, the high hardness of calcium silicate effectively suppresses the volume expansion of silicon particles, ensuring good cycling performance.

[0023] Existing technologies have shown that pre-lithiation of silicon suboxide with oxides (such as magnesium oxide) to form a magnesium silicate coating layer can improve first-cycle efficiency. These methods typically require nanoscale materials and are costly (the need for nanoscale materials arises from the increased contact area between silicon suboxide and the oxide, which improves the integrity of the magnesium silicate coating). Furthermore, these methods often require high temperatures of 1200°C, which can easily lead to excessive silicon crystallization, negatively impacting cycle performance. Our proposed method reduces silicon crystallite size by lowering the SiO disproportionation temperature (ideally 850-1000°C), followed by HF etching to obtain micron-sized porous silicon with a larger specific surface area, thus achieving lower-cost micron-sized materials. Moreover, the use of calcium oxide allows for a lower heat treatment temperature of only 900-1100°C during the coating heat treatment, effectively suppressing excessive silicon crystallization and preventing excessive crystallization that could negatively impact cycle performance, resulting in better cycle performance.

[0024] In summary, this invention improves the first-efficiency to a certain extent and greatly enhances the cycle stability of porous silicon anodes. Attached Figure Description

[0025] Figure 1 The XRD pattern is shown for 950pSi@20%CaO synthesized in Example 1.

[0026] Figure 2 This is a TEM image of 950pSi@20%CaO synthesized in Example 1.

[0027] Figure 3 The charge-discharge curves are for 950pSi@20%CaO synthesized in Example 1.

[0028] Figure 4 The charge-discharge curves of the 950pSi synthesized in Example 1 are shown for comparison.

[0029] Figure 5 The charge-discharge curves of 950pSi@20%MgO synthesized in Comparative Example 2 are shown.

[0030] Figure 6 Cyclic curves of the samples synthesized in Comparative Example 1, Comparative Example 2, and Example 1 are shown.

[0031] Figure 7 The XRD curves of the synthesized samples in Examples 1 and 2 are compared.

[0032] Figure 8 TEM images of the sample synthesized in Example 1 for comparison.

[0033] Figure 9 BET images of the sample synthesized in Example 1 are shown for comparison. Detailed Implementation

[0034] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0035] Example 1

[0036] Includes the following steps:

[0037] S1: Weigh 4.8 grams of SiO and treat it at 950°C for 2 hours in an inert atmosphere furnace, then allow it to cool naturally to room temperature. This is recorded as 950SiO. The inert atmosphere used is Ar (the same applies below; of course, other inert atmospheres, such as N2, can also be used).

[0038] S2: Weigh 4.8 g of 950SiO and disperse it in 200 mL of deionized water. Add 100 mL of anhydrous ethanol and 19.2 mL of HF (AR, 40%; Aladdin H116232). Stir for 4 hours, centrifuge, and dry in a vacuum oven at 80 °C for 12 hours. Record the sample as 950pSi.

[0039] S3: Ball mill 950pSi and 20wt% CaO (i.e., the mass percentage of CaO in the mixture of CaO and 950pSi is 20wt%; that is, the mass ratio of 950pSi to CaO is 8:2) for 2 hours.

[0040] S4: The powder obtained in S3 was heat-treated at 1000℃ for 2 hours under Ar atmosphere and recorded as 950pSi@20%CaO.

[0041] S5: Prepare a slurry by mixing the sample obtained in S4 with conductive carbon and binder in a mass ratio of 70:15:15. Then, uniformly coat the copper foil surface with the slurry and dry it in a vacuum drying oven at 80°C for 12 hours.

[0042] S6: Cut the electrode obtained in S5 into small circular pieces of a certain diameter, and assemble a button cell using lithium sheet as the counter electrode.

[0043] Example 2

[0044] Includes the following steps:

[0045] S1: Weigh 4.8 grams of SiO powder and treat it in an inert atmosphere furnace at 850°C for 5 hours. Then let it cool naturally to room temperature. This is recorded as 850SiO.

[0046] S2: Weigh 4.8 g of 850SiO and disperse it in 200 mL of deionized water. Add 100 mL of anhydrous ethanol and 10 mL of HF (AR, 40%). Stir for 4 hours, centrifuge, and dry in a vacuum oven at 80 °C for 12 hours. Record the sample as 850pSi.

[0047] S3: Ball mill 850pSi and 5wt% CaO together for 2 hours.

[0048] S4: The powder obtained in S3 was heat-treated at 1100℃ for 1 hour under an Ar atmosphere and recorded as 850pSi@5%CaO.

[0049] S5: Prepare a slurry by mixing the sample obtained in S4 with conductive carbon and binder in a mass ratio of 70:15:15. Then, uniformly coat the copper foil surface with the slurry and dry it in a vacuum drying oven at 80°C for 12 hours.

[0050] S6: Cut the electrode obtained in S5 into small circular pieces of a certain diameter, and assemble a button cell using lithium sheet as the counter electrode.

[0051] Example 3

[0052] Includes the following steps:

[0053] S1: Weigh 4.8 grams of SiO powder and treat it in an inert atmosphere furnace at 1000℃ for 1 hour. Then let it cool naturally to room temperature. This is recorded as 1000SiO.

[0054] S2: Weigh 4.8 g of 1000SiO and disperse it in 200 mL of deionized water. Add 100 mL of anhydrous ethanol and 60 mL of HF (AR, 40%). Stir for 4 hours, centrifuge, and dry in a vacuum oven at 80 °C for 12 hours. Record the sample as 1000pSi.

[0055] S3: Ball mill 1000pSi and 10wt% CaO together for 2 hours.

[0056] S4: The powder obtained in S3 was heat-treated at 900℃ for 5 hours under Ar atmosphere and recorded as 1000pSi@10%CaO.

[0057] S5: Prepare a slurry by mixing the sample obtained in S4 with conductive carbon and binder in a mass ratio of 70:15:15. Then, uniformly coat the copper foil surface with the slurry and dry it in a vacuum drying oven at 80°C for 12 hours.

[0058] S6: Cut the electrode obtained in S5 into small circular pieces of a certain diameter, and assemble a button cell using lithium sheet as the counter electrode.

[0059] Comparative Example 1:

[0060] As a control, uncoated porous silicon was synthesized.

[0061] S1: Weigh 4.8 grams of SiO and treat it in an inert atmosphere furnace at 950°C for 2 hours, then let it cool naturally to room temperature. This is recorded as 950SiO.

[0062] S2: Weigh 4.8 g of 950SiO and disperse it in 200 mL of deionized water. Add 100 mL of anhydrous ethanol and 19.2 mL of HF (AR, 40%). Stir for 4 hours, centrifuge, and dry in a vacuum oven at 80 °C overnight. Record the sample as 950pSi.

[0063] S3: Prepare a slurry by mixing 950pSi with conductive carbon and binder in a mass ratio of 70:15:15. Then, uniformly coat the copper foil surface with the slurry and dry it in a vacuum drying oven at 80°C for 12 hours.

[0064] S4: Cut the electrode obtained in S5 into small circular pieces of a certain diameter, and use lithium sheets as counter electrodes to assemble button cells.

[0065] Comparative Example 2:

[0066] As a comparison, porous silicon and magnesium oxide were processed using the same process to obtain pSi@MgO composite material.

[0067] S1: Weigh 4.8 grams of SiO and treat it in an inert atmosphere furnace at 950°C for 2 hours, then let it cool naturally to room temperature. This is recorded as 950SiO.

[0068] S2: Weigh 4.8 g of 950SiO and disperse it in 200 mL of deionized water. Add 100 mL of anhydrous ethanol and 19.2 mL of HF (AR, 40%). Stir for 4 hours, centrifuge, and dry in a vacuum oven at 80 °C overnight. Record the sample as 950pSi.

[0069] S3: Ball mill 950 pSi and 20 wt% MgO together for 2 hours.

[0070] S4: The powder obtained in S3 was heat-treated at 1000℃ for 2 hours under Ar atmosphere and recorded as 950pSi@20%MgO.

[0071] S5: Prepare a slurry by mixing the sample obtained in S4 with conductive carbon and binder in a mass ratio of 70:15:15. Then, uniformly coat the copper foil surface with the slurry and dry it in a vacuum drying oven at 80°C for 12 hours.

[0072] S6: Cut the electrode obtained in S5 into small circular pieces of a certain diameter, and assemble a button cell using lithium sheet as the counter electrode.

[0073] Performance testing:

[0074] Figure 1 The XRD pattern is shown for the 950pSi@20%CaO synthesized in Example 1. It can be seen that the calcium silicate formed in the product is a mixed phase of Ca3(Si3O9) and CaSiO3. Figure 2 The image shows a TEM image of the 950pSi@20%CaO synthesized in Example 1. It can be seen that a distinct calcium silicate coating layer, approximately 6 nm thick, is present in the image.

[0075] Figure 3 The image shows the charge-discharge curves of the 950pSi@20%CaO synthesized in Example 1 as the negative electrode of a lithium-ion battery. The electrolyte was a 1M LiPF6-based EC / DEC (volume ratio 1:1) solution with 5% FEC additive. The test current density was 50 mA / g, and the voltage window was 0.01–1.5 V. The capacity was 738 mAh / g, and the initial coulombic efficiency was 68.59%. Figure 4 and Figure 5 The first charge-discharge curves for the porous silicon (pSi) and pSi@20%MgO composite materials synthesized in Comparative Examples 1 and 2 are shown, respectively. Their capacities and initial coulombic efficiencies are 898.1 mAh / g (58.76%) and 474.1 mAh / g (59.82%), respectively. This indicates that, compared to Comparative Example 1, the method in Example 1 significantly improves the initial efficiency while maintaining an acceptable capacity reduction. In contrast, Comparative Example 2 shows a poorer improvement in initial efficiency and significantly reduces the specific capacity of the active material.

[0076] Figure 6 The cycling curves are for the samples synthesized in Example 1, Comparative Example 1, and Comparative Example 2. The current density for the first 10 cycles is 50 mA / g, and the current density thereafter is 1000 mA / g (which is a high current). The voltage window is 0.01-1.5V. It can be seen that the capacity of the sample in Comparative Example 1 decreased significantly after 200 cycles, while the capacities of Example 1 and Comparative Example 2 remained stable. This indicates that the long-cycle performance of Example 1 and Comparative Example 2 is superior to that of Comparative Example 1. After 400 cycles, the capacity retention rate of the sample in Example 1 (625.2 / 762.3 = 82%, i.e., the ratio of the specific capacity at the 400th cycle to the specific capacity at the 11th cycle) is much better than that of Comparative Example 2 (186.8 / 395.1 = 47.3%), demonstrating superior long-cycle performance. Furthermore, the initial capacity and first-efficiency of Example 1 (762.3 mAh / g, 68.59%) are both superior to those of Comparative Example 2 (474.1 mAh / g, 59.82%), further illustrating that the method of Example 1 can significantly improve the electrochemical performance of pSi.

[0077] Figure 7 The XRD patterns of the synthesized samples from Comparative Examples 1 and 2 are shown. The XRD patterns reveal that, in addition to the characteristic peak of Si, Comparative Example 1 exhibits a broad peak in the 16-25° range; this broad peak represents amorphous SiO2. It can be seen that when the MgO mass content is 20%, a magnesium silicate mixed phase, including MgSiO3 and Mg2SiO4, is formed in the sample of Comparative Example 2.

[0078] Figure 8 The TEM image shows the sample synthesized in Example 1 for comparison. It can be seen that the uncoated porous silicon exhibits obvious etching marks at its edges, indicating a porous structure.

[0079] Figure 9 To compare the BET of the sample synthesized in Example 1, it can be seen that the average pore size of the porous silicon is 8.09 nm, which is at the mesoporous level.

[0080] All raw materials (such as SiO) used in the above embodiments were commercially available.

[0081] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a pSi@CaO composite material, characterized in that, It comprises the following steps: S1: subjecting SiO powder to disproportionation heat treatment under a protective atmosphere; wherein the reaction temperature of the disproportionation heat treatment is 850-1000℃; S2: etching the powder obtained in step S1 with HF to etch SiO2 in the powder and form a porous structure, and separating the powder from HF after the reaction and drying, to obtain porous silicon powder pSi; S3: uniformly mixing the porous silicon powder obtained in S2 with CaO and subjecting to coating heat treatment in an inert atmosphere, to obtain pSi@CaO composite material; wherein the heat treatment corresponds to the reaction CaO+SiO2=CaSiO3; compared with pSi@MgO composite material obtained by uniformly mixing the porous silicon powder obtained in S2 with MgO and then subjecting to coating heat treatment in an inert atmosphere, the pSi@CaO composite material has higher specific capacity; In step S2, the etching is dispersing the powder obtained in step S1 in a mixed solvent of deionized water and anhydrous ethanol, and adding HF; Every 4.8 grams of powder obtained in step S1 is corresponding to dispersing in 200 mL of a mixed solvent of deionized water and 100 mL of anhydrous ethanol, and the corresponding added HF is a 40% HF solution of 10-60 mL.

2. The preparation method according to claim 1, characterized in that, In step S1, the reaction time of the disproportionation heat treatment is 1-5 hours.

3. The preparation method according to claim 2, characterized in that, In step S1, the disproportionation heat treatment is reacted at 950℃ for 2 hours.

4. The preparation method according to claim 1, characterized in that, In step S2, every 4.8 grams of powder obtained in step S1 is corresponding to dispersing in 200 mL of a mixed solvent of deionized water and 100 mL of anhydrous ethanol, and the corresponding added HF is a 40% HF solution of 19.2 mL.

5. The preparation method according to claim 1, characterized in that, For step S3, the mass percentage of CaO in the mixture obtained by mixing the porous silicon powder with CaO is 5%-30%.

6. The preparation method according to claim 5, characterized in that, For step S3, the mass percentage of CaO in the mixture obtained by mixing the porous silicon powder with CaO is 20%.

7. The preparation method according to claim 1, characterized in that, In step S3, the reaction temperature of the coating heat treatment is 900-1100℃, and the reaction time is 1-5 hours.

8. The method of claim 7, wherein the step of preparing is characterized by, In step S3, the coating heat treatment is heated at 1000℃ for 2 hours.

9. The method of claim 1, wherein the step of forming the first and second layers is performed by a method selected from the group consisting of: sputtering, evaporation, and chemical vapor deposition. In step S1, the protective atmosphere is Ar or N2.

10. The method of claim 1, wherein the step of forming the first and second layers is performed by a method selected from the group consisting of: sputtering, evaporation, and chemical vapor deposition. In step S2, the separation of the powder from HF is centrifugal separation, and the drying is vacuum drying.

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