Desolvation layer modified silicon-carbon negative electrode and preparation method thereof

Abstract

The invention relates to a desolventizing layer modified silicon-carbon negative electrode and a preparation method, the desolventizing layer modified silicon-carbon negative electrode comprises a silicon-carbon negative electrode, the silicon-carbon negative electrode comprises porous carbon mainly comprising mesopores and a silicon substrate attached in the pores of the porous carbon, and the desolventizing layer is covered on the surface of the silicon-carbon negative electrode. The desolventizing layer is an oxide of an amorphous active metal and a composite oxide of the amorphous active metal and lithium, the desolventizing layer at least covers the surface of the silicon substrate in the pores of the porous carbon, the desolventizing layer is made of amorphous titanium oxide, lithium titanate, niobium oxide, lithium niobate and titanium niobate, and after the electrolyte permeates into the pores of the porous carbon, the surface of the silicon substrate is coated with the desolventizing layer. And the lithium ions subjected to desolvation through the desolvation layer are alloyed with a silicon substrate. And the structural stability, the charge-discharge efficiency and the rate capability of the silicon-carbon negative electrode material are improved.

Description

Technical Field

[0001] The present invention relates to a silicon-carbon negative electrode with a modified desolvation layer and a preparation method thereof, belonging to the field of negative electrode materials for lithium-ion batteries. Background Art

[0002] As a secondary battery with high energy density, lithium-ion batteries are widely used in electric vehicles, wearable devices, and energy storage systems. Silicon-based negative electrode materials have attracted much attention due to their extremely high theoretical specific capacity (4200 mAh / g). However, during charge and discharge processes, they will undergo huge volume expansion (>300%), resulting in the collapse of the material structure, electrode polarization, the loss of electrical contact between the active material and the current collector, and the rapid attenuation of electrochemical performance. At the same time, silicon has poor intrinsic electron conductivity and ion conductivity, and its rate performance is poor at high current densities. To solve the above problems, researchers have proposed various solutions, such as preparing silicon-carbon composite materials. The silicon-carbon composite material can use carbon coating on the silicon material as a physical barrier to reduce the direct contact between silicon and the electrolyte, thereby inhibiting the excessive growth of the SEI film, reducing the decomposition and consumption of the electrolyte. Carbon coating can improve the conductivity, cycle stability, and rate performance. However, the carbon coating layer cannot avoid the contact between the electrolyte and silicon, which makes it difficult to fundamentally solve the problems of volume expansion of silicon negative electrode materials and the detachment of silicon particles from the electrode during charge and discharge.

[0003] The mainstream preparation method of silicon-carbon negative electrode materials is to deposit nanosilicon in porous carbon materials by CVD. However, the CVD method also has many problems. Currently, the porous carbon mainly consists of micropores and contains a small amount of mesopores. Due to the lack of capillary effect in the mesopores (2 - 50 nm) of the porous carbon, it is difficult for silane gas to enter the mesopore channels. Although the micropores (<2 nm) can adsorb silane gas, after depositing nanosilicon, the pore diameter becomes smaller, affecting the entry and rapid conduction of organic solvents and lithium ions, resulting in poor kinetic performance in current silicon-carbon negative electrodes.

[0004] Therefore, using porous carbon mainly composed of mesopores as a carrier for nanosilicon deposition and improving the kinetic performance of silicon-carbon negative electrodes while maintaining cycle stability has become a key technical bottleneck that urgently needs to be broken through in the preparation of high-performance silicon-carbon negative electrode materials. Summary of the Invention

[0005] The technical problem to be solved by the present invention is: to overcome the deficiencies of the prior art and provide a silicon-carbon negative electrode with a modified desolvation layer, including a silicon-carbon negative electrode. The silicon-carbon negative electrode includes porous carbon mainly composed of mesopores and a silicon matrix attached to the pores of the porous carbon. It is characterized in that the surface of the silicon-carbon negative electrode is further covered with a desolvation layer, and the desolvation layer is an amorphous oxide of an active metal or an amorphous composite oxide of an active metal and lithium, and the desolvation layer covers at least the surface of the silicon matrix in the pores of the porous carbon.

[0006] The thickness of the desolvation layer is 0.2 to 10 nm.

[0007] The active metals include titanium and niobium, and the desolvation layer includes amorphous titanium oxide, niobium oxide, lithium titanate, lithium niobate, and titanium niobate.

[0008] The pore size of the porous carbon is mainly distributed in the range of 10 to 100 nm, preferably, the pore size of the porous carbon is mainly distributed in the range of 30 to 50 nm.

[0009] The desolvation layer shields the contact between the electrolyte solution entering the pores of the porous carbon and the silicon matrix. After the electrolyte penetrates into the pores of the porous carbon, the lithium ions after desolvation through the amorphous protective layer then alloy with the silicon matrix, improving the structural stability of the silicon-carbon negative electrode, as well as the charge-discharge efficiency and rate performance of the silicon-carbon negative electrode.

[0010] The preparation method of the silicon-carbon negative electrode according to the present invention includes the following steps:

[0011] Coat the silicon-carbon negative electrode powder by atomic layer deposition technology to obtain a silicon-carbon negative electrode coated with a desolvation layer.

[0012] Optionally, it includes: K1. Place the silicon-carbon negative electrode powder in a porous container, put the porous container into the reaction chamber, displace the gas in the reaction chamber with an inert gas, and evacuate; K2. Rotate the porous container to achieve the effect of dispersing the silicon-carbon negative electrode powder, alternately introduce the first precursor and the oxygen source gas into the reaction chamber in a pulsed manner with an inert gas, purge the residual gas with an inert gas between alternations, and evacuate. The temperature of the reaction chamber is set to 50 to 300 °C, and the pressure after introducing the first precursor and the oxygen source gas is set to 40 to 150 Pa. Repeat step K2 until the desolvation layer reaches 0.2 to 10 nm.

[0013] In step K2, the negative pressure state reached after evacuating and then introducing the inert gas is -0.5 MPa to -1 MPa, and it is maintained for a period of 0.5 - 2 h.

[0014] The first precursor is one or a mixture of several of volatile metal alkoxides, metal organic compounds, halides, alcoholates, and metal β-diketonate complexes. Among them, the metal elements in the metal alkoxides, metal organic compounds, halides, alcoholates, and metal β-diketonate complexes are one or two of titanium, niobium, lithium, and titanium and niobium.

[0015] Compared with the prior art, the beneficial effects of the present invention are:

[0016] (1) The preparation method described in the present invention realizes a micro-vacuum environment in the pores of the silicon-carbon negative electrode through multiple vacuum extractions, and dispersedly introduces titanium source and oxygen source gases, which can achieve uniform deposition of titanium dioxide coating in the mesopores of the silicon-carbon negative electrode, effectively alleviating the volume expansion effect of silicon during charge and discharge, and improving the cycle stability of the silicon-carbon negative electrode material;

[0017] (2) The silicon-carbon negative electrode of the present invention uses porous carbon mainly composed of mesopores, which helps lithium ions to penetrate deep into the pores and migrate quickly.

[0018] (3) The amorphous titanium oxide, niobium oxide, lithium titanate, lithium niobate, and titanium niobate coated on the surface of the silicon matrix shield the contact between the electrolyte entering the pores of the porous carbon and the silicon matrix. After the electrolyte solution penetrates into the pores of the porous carbon, the lithium ions after desolvation by the amorphous titanium oxide, niobium oxide, lithium titanate, lithium niobate, and titanium niobate then alloy with the silicon matrix. This avoids the absolute volume change of the silicon-carbon negative electrode during charge and discharge, improves the structural stability of the silicon-carbon negative electrode, as well as the charge and discharge efficiency and rate performance of the silicon-carbon negative electrode;

[0019] Utilizing the zero-strain characteristics and the feature of accelerating lithium-ion transport of the amorphous structure of titanium oxide and niobium oxide, a uniform desolvation coating layer is realized on the silicon surface by the ALD method, enabling lithium ions to quickly desolvate on the surface of the coating layer and be transported to the surface of the silicon particles. It has a faster lithium-ion transport ability compared to desolvation and then transport on the silicon surface. Description of the Drawings

[0020] Figure 1 is the electron image of the silicon-carbon negative electrode coated with TiO2 of the present invention;

[0021] Figure 2 is the element distribution diagram of the silicon-carbon negative electrode with a modified desolvation layer of the present invention;

[0022] Figure 3 is the discharge capacity diagram of Example 1, Comparative Example 2, and Example 5 of the present invention as electrode materials in a CR2032 half-cell;

[0023] Figure 4 is the battery cycle life diagram of Example 1, Comparative Examples 1 - 2 of the present invention as electrode materials in a CR2032 half-cell. Detailed Embodiments

[0024] Example 1

[0025] The preparation method of the silicon-carbon negative electrode with a modified desolvation layer described in the present invention includes the following steps:

[0026] 1) Prepare the silicon-carbon negative electrode

[0027] Select a commercial silicon-carbon anode powder, such as the silicon-carbon anode disclosed in CN114079045B.

[0028] Select the silicon-carbon anode powder prepared by the method in CN117438558A. This silicon-carbon anode includes a porous carbon matrix and a nano-silicon coating layer located inside the pores of the porous carbon matrix.

[0029] Or select the silicon-carbon anode powder prepared by the method in CN202411943643.X. This silicon-carbon anode includes silicon nanowires and a carbon layer coated on the surface of the silicon nanowires.

[0030] Or select the silicon-carbon anode powder prepared by the method in CN118016835A. This silicon-carbon anode includes silicon nanoparticles and a carbon layer coated on the surface of the silicon nanoparticles.

[0031] 2) Coating an amorphous titanium dioxide layer

[0032] K1. Place the silicon-carbon anode powder in a porous container, put the porous container into the reaction chamber, displace the gas in the reaction chamber with an inert gas, and evacuate. K2. Rotate the porous container to achieve the effect of dispersing the silicon-carbon anode powder. Load the first precursor and the oxygen source gas into the reaction chamber alternately in a pulsed manner with an inert gas. Purge the residual gas with an inert gas between alternations and evacuate. Set the temperature of the reaction chamber to 160 - 300 °C, and set the pressure to 40 - 150 Pa after loading the first precursor and the oxygen source gas. Repeat this step K2 until the amorphous titanium dioxide layer reaches 5 nm.

[0033] The first precursor is TiCl4, and the oxygen source is water vapor.

[0034] As Figure 1 shown is the silicon-carbon anode coated with TiO2, and the titanium dioxide layer is amorphous TiO2. As Figure 2 shown, the silicon-carbon anode modified with the desolvation layer has a uniform distribution of Ti elements.

[0035] 3) Preparation of the negative electrode

[0036] Mix the silicon-carbon anode coated with an amorphous titanium dioxide layer, conductive carbon black, and polyacrylic acid (PAA) in a weight ratio of 8:1:1, and disperse them in deionized water to form a uniform slurry. Then cast the slurry onto a copper foil by the doctor blade method and vacuum dry it at 60 °C for 12 h to obtain the negative electrode sheet.

[0037] In this example, when the coating thickness of the amorphous titanium dioxide layer is small, the ineffective weight of the silicon-carbon anode can be reduced.

[0038] Examples 2 - 5

[0039] The method for preparing a silicon-carbon negative electrode with a modified desolvation layer of the present invention adopts the steps of Example 1, except that the first precursor and the oxygen source gas are replaced by the first precursor and the oxygen source in Table 1.

[0040] The first precursor is one or a mixture of volatile metal alkylamino salts, metal organic compounds, halides, alcohol salts, and metal beta-diketone complexes.

[0041] The metal elements in the metal alkylamino salt, metal organic compound, halide, alkoxide, and metal β-diketonate complex are one or two of titanium (Ti), niobium (Nb), lithium (Li), and titanium (Ti) and niobium (Nb). The thickness of the desolvation layer is 5 nm.

[0042] Preferably, in step K2 of embodiment 1, the negative pressure state to which the inert gas is introduced after vacuum is 0.5 MPa to 1 MPa, and is maintained for a period of 0.5 to 2 hours.

[0043] Table 1

[0044]

[0045] O t Bu represents tert-butyl alcohol, and OEt represents ethoxy.

[0046] Comparative Example 1

[0047] The preparation method of the silicon-carbon negative electrode with modified desolvation layer adopts the steps of Example 1, except that the first precursor is replaced by AlCl3.

[0048] Comparative Example 2

[0049] The method for preparing a silicon-carbon negative electrode with a modified desolvation layer of the present invention adopts the steps of Example 1, except that after step 2), the temperature is raised to 350° C. to 800° C. to convert amorphous TiO2 into anatase TiO2.

[0050] Example 6

[0051] A half-cell was composed of a lithium metal sheet and a copper foil, 1M LiTFSIDOL / DME (volume ratio of 1:1) was used as the electrolyte, and the negative electrode sheets prepared in Examples 1 to 5 and Comparative Examples 1 to 2 and a commercial silicon-carbon composite negative electrode (BSO-2) were respectively assembled into CR2032 half-cells in an argon atmosphere glove box, and their electrochemical properties were tested.

[0052] Using the Neware battery test system, the MIHW-B was subjected to constant current charge / discharge tests at room temperature under the test conditions of 0.1C, with corresponding voltages of 1.5V or 0.8V. As shown in Table 2, the rate performance of the silicon-carbon negative electrode after TiO2 coating is better than that of the uncoated silicon-carbon negative electrode.

[0053] Table 2

[0054]

[0055] As Figure 3 shown, the discharge capacities of Example 1 (ALD-amorphous TiO2), Comparative Example 2 (ALD-anatase TiO2), and Example 5 (ALD-TiNb2O7) as electrode materials were tested in CR2032 half-cells at different current densities. At high current densities (such as 5.9C, 11.8C), Example 5 (ALD-TiNb2O7) as an electrode material has more obvious performance advantages in the CR2032 half-cell, and its capacity retention rate is much higher than that of the other two materials. The CR2032 half-cell fabricated with Example 5 (ALD-TiNb2O7) as the electrode material showed the best cycle stability during multiple charge-discharge cycles. Even at high current densities, its capacity decay was relatively small. In contrast, the CR2032 half-cell fabricated with Comparative Example 2 (ALD-anatase TiO2) as the electrode material had poor cycle stability and fast capacity decay.

[0056] As Figure 4 shown, the silicon-carbon composite material (ALD-Al2O3) prepared in Comparative Example 1, the silicon-carbon composite material (ALD-TiO2) prepared in Example 1, and the silicon-carbon composite material (uncoated) prepared in Comparative Example 2 were fabricated into negative electrode sheets and assembled with NCM811 positive electrode sheets into a 5Ah soft-pack full cell for cycle testing at a test rate of 1C and a charging voltage of 2.75 - 4.25V. After 1000 long cycles, the silicon-carbon composite material (ALD-TiO2) showed a specific capacity retention rate of up to 90% during the entire cycle, the silicon-carbon composite material (ALD-Al2O3) showed a specific capacity retention rate of up to 83% during the entire cycle, and the silicon-carbon composite material (uncoated) showed a specific capacity retention rate of 58% during the entire cycle. Moreover, the initial specific capacity of the silicon-carbon composite material (ALD-TiO2) was 1933 mAh / g, the initial specific capacity of the silicon-carbon composite material (ALD-Al2O3) was 1844 mAh / g, and the initial specific capacity of the silicon-carbon composite material (uncoated) was 1803 mAh / g. From the two dimensions of cycle stability and specific capacity, the silicon-carbon composite material (ALD-TiO2) demonstrated significant advantages and is suitable for high-performance battery applications.

[0057] In the present invention, the description of the direction and relative positional relationship of the structure, such as the description of front, back, left, right, up, and down, does not constitute a limitation to the present invention and is only for convenience of description.

Claims

1. A silicon-carbon negative electrode with a modified desolvation layer, comprising a silicon-carbon negative electrode, the silicon-carbon negative electrode including mesoporous-dominated porous carbon and a silicon matrix attached to the pores of the porous carbon, characterized in that, The surface of the silicon-carbon negative electrode is further covered with a desolvation layer, and the desolvation layer is an amorphous oxide of an active metal, an amorphous composite oxide of an active metal and lithium. The desolvation layer covers at least the surface of the silicon matrix in the pores of the porous carbon. The active metal includes titanium and niobium, and the desolvation layer includes amorphous titanium oxide, niobium oxide, lithium titanate, lithium niobate, and titanium niobate.

2. The silicon-carbon negative electrode with a modified desolventized layer according to claim 1, characterized in that, The thickness of the desolvation layer is 0.2 to 10 nm.

3. The silicon-carbon negative electrode with a modified desolventized layer according to claim 1, wherein The silicon matrix includes nano-silicon particles, silicon nanowires, or silicon thin films.

4. The preparation method of the silicon-carbon negative electrode with a modified desolventized layer according to any one of claims 1 to 3, characterized in that, It includes the following steps: Coat the silicon-carbon negative electrode powder by atomic layer deposition technology to obtain a silicon-carbon negative electrode coated with a desolvation layer.

5. The preparation method of the silicon-carbon negative electrode with a modified desolventizing layer according to claim 4, characterized in that, It includes: K1. Place the silicon-carbon negative electrode powder in a porous container, put the porous container into the reaction chamber, replace the gas in the reaction chamber with an inert gas, and evacuate. K2. Rotate the porous container to achieve the effect of dispersing the silicon-carbon negative electrode powder. Load the first precursor and the oxygen source gas into the reaction chamber alternately in a pulsed manner with an inert gas. Purge the residual gas with an inert gas between the alternations and evacuate. Set the temperature of the reaction chamber to 50 to 300 °C, and set the pressure to 40 to 150 Pa after loading the first precursor and the oxygen source gas. Repeat step K2 in a cycle until the desolvation layer reaches 0.2 to 10 nm.

6. The preparation method of the silicon-carbon negative electrode with a modified desolventized layer according to claim 5, characterized in that, In step K2, the negative pressure state reached after evacuating and then passing the inert gas is -0.5 MPa to -1 MPa, and it is maintained for a period of 0.5 - 2 h.

7. The preparation method of the silicon-carbon negative electrode with a modified desolventized layer according to claim 6, characterized in that, The first precursor is one or a mixture of several of volatile metal alkoxides, metal organic compounds, halides, alcoholates, and metal β-diketonate complexes. Among them, the metal elements in the metal alkoxides, metal organic compounds, halides, alcoholates, and metal β-diketonate complexes are one or two of titanium, niobium, lithium, and titanium and niobium.

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