Method for preparing carbon / silicon composite negative electrode material in one step

Abstract

The application discloses a one-step method for preparing a carbon / silicon composite negative material, and specifically comprises the following steps: step 1, placing porous carbon in a rotary kiln, heating to a set temperature under an inert atmosphere, and circulating two kinds of mixed gases in sequence; step 2, feeding a pyrolysis carbon source and a carrier gas, depositing after heat preservation, and realizing pyrolysis carbon coating; cooling to room temperature, discharging, and obtaining the silicon-carbon negative material. The one-step method is simple and easy to enlarge, and solves the defect of high activity in the practical application of superfine nanosilicon.

Description

Technical Field

[0001] This invention belongs to the technical field of lithium-ion battery anode active materials, and relates to a one-step method for preparing carbon / silicon composite anode materials. Background Technology

[0002] Silicon-carbon anode materials are one of the key material technologies for lithium-ion batteries to break through the 300Wh / kg limit. In recent years, with the gradual maturation of silicon-carbon anode material preparation technology and the expansion of production capacity, they have been applied on a large scale in power batteries and digital 3C products. However, the particle breakage and electrode pulverization caused by the huge volume expansion of silicon anodes have limited their further application. To address this shortcoming, commonly used methods include nano-sizing, structural design, and composite with carbon materials. Among these, nano-sizing is one of the most important solutions. The size and crystallinity of nano-silicon play a decisive role in the final performance of silicon-carbon anode materials. The smaller the size of the nano-silicon, the smaller its volume expansion effect. Literature reports that when the size of nano-silicon is less than 30nm, its volume expansion is greatly suppressed.

[0003] Currently, nano-silicon is typically prepared using methods such as ball milling, vapor deposition, and vacuum thermal evaporation. Among these, vapor deposition has attracted widespread attention due to its ability to produce nano-silicon with a uniform particle size distribution ranging from 1 to 1000 nm. Nanomaterials generally possess high surface energy, especially nano-silicon with particle sizes below 10 nm, which makes it highly susceptible to spontaneous combustion in air. Furthermore, it exhibits poor storage performance, is prone to oxidation when exposed to air, and its electrochemical performance deteriorates rapidly. These processing difficulties limit the application of ultrafine nano-silicon in silicon-carbon anodes.

[0004] Currently, the main methods to address this defect are passivation, organic liquid sealing, and compounding with an inert second phase to reduce activity. However, these methods significantly increase production costs due to the additional steps involved. Summary of the Invention

[0005] The purpose of this invention is to provide a one-step method for preparing carbon / silicon composite anode materials. The materials prepared by this method can remain stable in air without degradation, and the process is simple and easy to scale up.

[0006] The technical solution adopted in this invention is a one-step method for preparing carbon / silicon composite anode materials, specifically including the following steps:

[0007] Step 1: Place the porous carbon in a rotary kiln and heat it to the set temperature under an inert atmosphere, then circulate the two mixed gases in sequence.

[0008] Step 2: Introduce pyrolytic carbon source and carrier gas, maintain the temperature and deposit to achieve pyrolytic carbon coating; cool down to room temperature and discharge the material to obtain silicon-carbon anode material.

[0009] The invention is further characterized by:

[0010] In step 1, the inert atmosphere is nitrogen, and the temperature is raised to 480℃-600℃.

[0011] In step 1, the two mixed gases are gas A, which is composed of silane gas and hydrogen gas, and gas B, which is composed of nitrogen gas and oxidizing gas. Each time gas A and gas B are introduced, it is recorded as one cycle. The number of cycles is 2 to 5.

[0012] In step 1, the flow rate ratio of silane gas to hydrogen gas is 1:(0.1-10), the time ratio of mixed gas A to mixed gas B is 10:(0.5-2), and the flow rate ratio of mixed gas A to mixed gas B is 1:(0.01-0.2).

[0013] In gas mixture B, the oxidizing gas is one of oxygen, water vapor, or chlorine.

[0014] In step 2, the pyrolysis carbon deposition temperature is between 700℃ and 900℃, the pyrolysis carbon source is one of acetylene, acetone, or cyclohexane, and the deposition time is 60 min to 240 min.

[0015] The beneficial effects of this invention are that, using porous carbon as a matrix, an oxidizing gas is intermittently introduced during the silane deposition process to passivate the nano-silicon generated by silane pyrolysis and inhibit the activity of the nano-silicon; the process of this invention is simple and easy to scale up; the porous carbon matrix provides active sites and expansion space for silane deposition; ultrafine nano-silicon is generated in situ in the pores of porous carbon during the silane deposition process, and the nano-silicon is passivated by intermittently introducing an oxidizing gas. Attached Figure Description

[0016] Figure 1 The pore size distribution of commercial porous carbon-1

[0017] Figure 2 It is the surface morphology of commercially available porous carbon 3;

[0018] Figure 3 It is the pore size distribution of commercially available porous carbon-3;

[0019] Figure 4 This is the first charge-discharge curve of the silicon-carbon finished product and samples with different standing days prepared in Example 4 of the method for preparing carbon / silicon composite anode material in one step according to the present invention. Detailed Implementation

[0020] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0021] The present invention provides a one-step method for preparing carbon / silicon composite anode materials, comprising the following steps:

[0022] Step 1: Place the porous carbon in a rotary kiln and heat it to a certain temperature under an inert atmosphere. Then, introduce silane and hydrogen gas for a period of time, stop introducing the gas, introduce nitrogen and oxidizing gas for a period of time, stop introducing the gas, then introduce silane and hydrogen gas again, stop introducing the gas, and then introduce nitrogen and oxidizing gas again for a period of time. Repeat this cycle 2-5 times. This ensures that most of the ultrafine nano-silicon undergoes a certain degree of passivation. However, the number of cycles should not be too high, as this could lead to excessive oxidation of the nano-silicon, affecting the performance of the final product.

[0023] In step 1, the inert atmosphere is nitrogen, and the temperature is raised to 480-600℃. If the temperature is too low, the silane decomposition rate will be too low, and if the temperature is too high, the silane will decompose too quickly and deposit on the surface.

[0024] A mixture of silane gas and hydrogen is formed, and a mixture of nitrogen gas and oxidizing gas is formed, and the flow rate ratio of silane gas to hydrogen gas is 1:(0.1-10). The time ratio of gas mixture A to gas mixture B is 10:(0.5-2). The flow rate ratio of gas mixture A to gas mixture B is 1:(0.01-0.2).

[0025] Oxidizing gases include oxygen, water vapor, and chlorine, with oxygen being the preferred option.

[0026] Step 2: Continue heating, introduce pyrolytic carbon source and carrier gas, and maintain the temperature for a period of time to achieve pyrolytic carbon coating; cool down to room temperature, discharge the material and obtain silicon-carbon anode material.

[0027] In step 2, the pyrolysis carbon deposition temperature is between 700-900℃, the pyrolysis carbon source is acetylene, acetone, cyclohexane, etc., and the deposition time is 60-240 min. The carrier gas is hydrogen.

[0028] Example 1

[0029] Commercial porous carbon 1, specific surface area 1500m 2 / g, pore volume 0.72cm 3 / g, average pore size 2.3nm.

[0030] 1 kg of commercial porous carbon 1 was placed in a rotary kiln. After purging with inert gas, the temperature was raised to 480℃ under an inert atmosphere. SiH4 / H2 was introduced at a rate of 2 / 5 L / min for 120 min. After stopping, N2 / O2 was introduced at a rate of 2 / 0.3 L / min for 15 min. Then, SiH4 / H2 was introduced at a rate of 2 / 5 L / min for 120 min. After stopping, N2 / O2 was introduced at a rate of 2 / 0.3 L / min for 15 min. This cycle was repeated four times in total. The temperature was then raised to 700℃ under an inert atmosphere. C2H2 / N2 was introduced at a rate of 1 / 3 L / min for 120 min. The acetylene introduction and heating were stopped. The material was then cooled to obtain the final silicon-carbon anode material.

[0031] Comparative Example 1

[0032] Compared to Example 1, during the alternation phase, N2 was introduced at a rate of 2.3 L / min, but no oxygen was introduced; all other experimental conditions remained the same.

[0033] Example 2

[0034] Compared with Example 1, N2 / O2 = 2 / 0.1 L / min was introduced for 15 min, while other parameters remained unchanged.

[0035] Example 3

[0036] Compared with Example 1, SiH4 / H2 = 1.5 / 8 L / min, with other parameters remaining unchanged.

[0037] Example 4

[0038] Commercial porous carbon-2, specific surface area 300m 2 / g, pore volume 0.6cm 3 / g, average pore size 12nm.

[0039] 1 kg of commercial porous carbon-2 was placed in a rotary kiln. After purging with inert gas, the temperature was raised to 480℃ under an inert atmosphere. SiH4 / H2 was introduced at a rate of 1 / 5 L / min for 150 min. After stopping, N2 / O2 was introduced at a rate of 2 / 0.2 L / min for 20 min. Then, SiH4 / H2 was introduced at a rate of 1 / 5 L / min for 150 min. After stopping, N2 / O2 was introduced at a rate of 2 / 0.3 L / min for 20 min. This cycle was repeated three times. The temperature was then raised to 700℃ under an inert atmosphere. C2H2 / N2 was introduced at a rate of 1 / 3 L / min for 120 min. The acetylene introduction and heating were stopped. The material was then cooled to obtain the final silicon-carbon anode material.

[0040] Meanwhile, we placed the sample from Example 4 in dry air and tested its electrochemical performance after 1 day, 3 days, and 7 days.

[0041] Example 5

[0042] Commercial porous carbon-3, specific surface area 2700m 2 / g, pore volume 1.3cm 3 / g, average pore size 2.1nm.

[0043] 1 kg of commercial porous carbon-3 was placed in a rotary kiln. After purging with inert gas, the temperature was raised to 480℃ under an inert atmosphere. SiH4 / H2 was introduced at a rate of 1 / 10 L / min for 120 min. After stopping, N2 / O2 was introduced at a rate of 2 / 0.1 L / min for 20 min. Then, SiH4 / H2 was introduced at a rate of 1 / 1 L / min for 120 min. After stopping, N2 / O2 was introduced at a rate of 2 / 0.1 L / min for 20 min. This cycle was repeated five times in total. The temperature was then raised to 700℃ under an inert atmosphere. C2H2 / N2 was introduced at a rate of 1 / 3 L / min for 120 min. The acetylene introduction and heating were stopped. The material was then cooled to obtain the final silicon-carbon anode material.

[0044] Button-type lithium-ion batteries were assembled using the silicon-carbon anode materials provided in Examples 1-5, respectively. The raw materials used to assemble the lithium-ion batteries were the same. The positive electrode was a lithium sheet, and the current collector was a copper foil. After assembly, the initial charge specific capacity and initial coulombic efficiency of each group of lithium-ion batteries were tested.

[0045] Table 1 Electrochemical performance and physical property tests of Examples 1-5

[0046]

[0047] Table 2 Electrochemical performance tests after standing for different days in Example 4

[0048]

[0049] Table 3 Electrochemical performance tests of Comparative Example 1 after standing for different days

[0050]

[0051]

[0052] Figure 1 As can be seen, the pore size distribution of commercial porous carbon 1 is extremely narrow, basically below 5 nm; Figure 2 Commercial porous carbon 3 particles can be observed to be smooth, with some surfaces showing traces of etching. Figure 3 As can be seen, the pore size of commercially available porous carbon is below 5 nm; Figure 4 As can be seen, the sample exhibits a typical silicon charge-discharge plateau, with minimal capacity variation and essentially stable performance across different resting days.

[0053] Table 1 shows that the porous carbon / silicon anode material prepared by passivated ultrafine nano-silicon exhibits high capacity and high initial efficiency, and its capacity remains essentially unchanged after 7 days of standing, with significantly improved air stability. Table 2 shows the prepared samples without passivation. After prolonged standing in air, the capacity and initial efficiency decreased significantly, indicating that the nano-silicon had undergone denaturation and performance degradation.

[0054] The preparation method provided by this invention involves intermittently introducing an oxidizing gas during silane vapor deposition to passivate the surface of the nano-silicon, thereby inhibiting its activity. Furthermore, porous carbon is used as the matrix, providing active sites and expansion space for silane deposition, significantly reducing the material's volume expansion. Subsequently, pyrolytic carbon is further coated onto the material surface to reduce specific surface area and improve conductivity. The preparation process is simple, easily scaled up, and the resulting silicon-carbon anode material exhibits low expansion and long cycle life.

[0055] This invention utilizes the intermittent introduction of a weak oxidizing gas during the silane vapor deposition process to passivate ultrafine nano-silicon, and further reduces the activity of ultrafine nano-silicon by isolating the nano-silicon from air through pyrolytic carbon coating. The one-step process is simple, easy to scale up, and solves the problem of high activity in the practical application of ultrafine nano-silicon.

Claims

1. A method for preparing carbon / silicon composite anode materials in one step, characterized in that: Specifically, the steps include the following: Step 1: Place porous carbon in a rotary kiln and heat it to a set temperature under an inert atmosphere. Then, circulate two mixed gases sequentially. In Step 1, the inert atmosphere is nitrogen, and the temperature is raised to 480℃-600℃. In Step 1, the two mixed gases are a mixture of silane gas and hydrogen gas A and a mixture of nitrogen gas and an oxidizing gas B. Each introduction of mixed gas A and mixed gas B is counted as one cycle, and the number of cycles is 2 to 5. Step 2: Introduce pyrolytic carbon source and carrier gas, maintain the temperature and deposit to achieve pyrolytic carbon coating; cool down to room temperature and discharge the material to obtain silicon-carbon anode material.

2. The method for preparing carbon / silicon composite anode material in one step according to claim 1, characterized in that: In step 1, the flow rate ratio of silane gas to hydrogen gas is 1:(0.1-10), the time ratio of mixed gas A to mixed gas B is 10:(0.5-2), and the flow rate ratio of mixed gas A to mixed gas B is 1:(0.01-0.2).

3. The method for preparing carbon / silicon composite anode material in one step according to claim 1, characterized in that: In the mixed gas B, the oxidizing gas is one of oxygen, water vapor, or chlorine.

4. The method for preparing carbon / silicon composite anode material in one step according to claim 1, characterized in that: In step 2, the pyrolysis carbon deposition temperature is between 700℃ and 900℃, the pyrolysis carbon source is one of acetylene, acetone, and cyclohexane, and the deposition time is 60min to 240min.

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