Silicon composite material and use thereof

Abstract

This invention provides a silicon composite material and its application. The silicon composite material contains gallium and indium, and the sum of the mass percentages of gallium and indium in the silicon composite material is 0.05-0.2%. When the negative electrode sheet containing this silicon composite material is applied to a battery, the silicon composite material is less prone to expansion and can form a stable SEI film, which can improve the cycle performance of the battery.

Description

Technical Field

[0001] This invention relates to the field of new energy technology, and in particular to a silicon composite material and its applications. Background Technology

[0002] Since their commercialization, lithium-ion batteries (LIBs) have become the dominant electrochemical energy storage system. To improve the energy density of lithium-ion batteries, silicon (Si) is considered one of the promising candidates to replace commercial graphite due to its high theoretical capacity.

[0003] However, silicon is prone to huge volume changes during the lithium insertion / extraction process in the battery, which can lead to repeated rupture and reconstruction of the SEI film, which is detrimental to the structural stability of the negative electrode and thus to the cycle performance of the battery. Summary of the Invention

[0004] This invention provides a silicon composite material. When the negative electrode sheet containing this silicon composite material is applied to a battery, the silicon composite material does not easily expand and can form a stable SEI film, which can improve the cycle performance of the battery.

[0005] The present invention provides a silicon composite material comprising liquid gallium and indium, wherein the sum of the mass percentages of gallium and indium in the silicon composite material is 0.05-0.2%.

[0006] The silicon composite material as described above, wherein, based on the total mass of gallium and indium, the mass percentage of gallium is 68-74% and the mass percentage of indium is 26-32%.

[0007] The silicon composite material described above includes a silicon core, an intermediate layer, and an outer layer;

[0008] The intermediate layer is located on at least a portion of the surface of the silicon core, and the outer layer is located on at least a portion of the surface of the intermediate layer;

[0009] The intermediate layer comprises liquid gallium and indium, the outer layer comprises a metal-organic hybrid glass, and the silicon core is a micron-sized silicon material.

[0010] The silicon composite material described above, wherein the Dv50 of the silicon core is 5-30 μm;

[0011] Preferably, the Dv50 of the silicon core is 20-30 μm.

[0012] The silicon composite material described above, wherein the specific surface area of ​​the silicon composite material is 200-2000 m². 2 / g; and / or,

[0013] The silicon composite material has a pore size of 1.3-2.7 nm; and / or,

[0014] The Dv50 of the silicon composite material is 10-50 μm; and / or,

[0015] The aspect ratio of the silicon composite material is 1-5; and / or,

[0016] The CO2 adsorption enthalpy of the silicon composite material is 10-40 kJ / mol.

[0017] The silicon composite material described above, wherein the specific surface area of ​​the silicon composite material is 800-2000 m². 2 / g; and / or,

[0018] The silicon composite material has a Dv50 of 35-50 μm; and / or,

[0019] The aspect ratio of the silicon composite material is 1-2; and / or,

[0020] The CO2 adsorption enthalpy of the silicon composite material is 15-30 kJ / mol.

[0021] In the silicon composite material described above, the mass ratio of the silicon core, the metal-organic hybrid glass, and the liquid metal is (50-100):(5-20):1.

[0022] Preferably, in the silicon composite material, the mass ratio of silicon core, metal-organic hybrid glass and liquid metal is (70-90):(8-12):1.

[0023] The silicon composite material as described above, wherein the metal-organic hybrid glass comprises metal ions and ligands, wherein the metal ions include at least one selected from copper ions, zinc ions, cobalt ions, iron ions, ferrous ions, zirconium ions, aluminum ions, and chromium ions, and the ligands include at least one selected from 1,3,5-benzenetricarboxylic acid, 2'-amino-[1,1':4',1”-terphenyl]-4,4”-dicarboxylic acid, terephthalic acid, dimethylimidazole, 2,5-dimethylterephthalic acid, 2,5-diaminoterephthalic acid, and 2-amino-4,4'-biphenylcarboxylic acid;

[0024] And / or, the micron-sized silicon material is at least one of micron-sized silicon carbide, micron-sized elemental silicon, micron-sized silicon oxide, micron-sized silicon nitride composite, and micron-sized silicon alloy.

[0025] The present invention provides a negative electrode sheet, comprising a negative electrode current collector and a negative electrode active layer located on at least one surface of the negative electrode current collector, the negative electrode active layer comprising a negative electrode active material, the negative electrode active material comprising a silicon composite material as described above.

[0026] In the negative electrode sheet described above, the mass percentage of the silicon composite material in the negative electrode active layer is 2-50%.

[0027] And / or, the sum of the mass percentages of gallium and indium is 0.01-0.04%; preferably, in the negative electrode active layer, the mass percentages of silicon, gallium and indium are (1-1.8):(0.0136-0.0148):(0.0052-0.0064).

[0028] In the negative electrode sheet described above, the ratio of peak height to peak width at the bottom of the color spectrum of the negative electrode sheet is greater than 40:1.

[0029] The present invention provides a battery comprising a negative electrode as described above.

[0030] The battery described above further includes an electrolyte comprising lithium hexafluorophosphate, wherein the concentration of lithium hexafluorophosphate in the electrolyte is c, mol / L; and the mass percentage w of the silicon composite material in the negative electrode sheet satisfies:

[0031] w:c=(10-30):1;

[0032] Preferably, w:c = (15-25):1.

[0033] The battery as described above, wherein the ohmic resistance of the battery is <34mΩ, the film resistance is <13mΩ, and the charge transfer resistance is <30mΩ;

[0034] Preferably, the battery has an ohmic impedance of <33mΩ, a membrane impedance of <12.5mΩ, and a charge transfer impedance of <20mΩ.

[0035] The silicon composite material of the present invention comprises liquid gallium and indium, wherein the sum of the mass percentages of gallium and indium in the silicon composite material is 0.05-0.2%. When the negative electrode sheet comprising this silicon composite material is applied to a battery, the silicon composite material is less prone to expansion and can form a stable SEI film, which can improve the battery's initial efficiency and cycle performance. Attached Figure Description

[0036] To more clearly illustrate the technical solutions in the embodiments of the present invention or related technologies, the accompanying drawings used in the description of the embodiments of the present invention or related technologies are briefly introduced below. Obviously, the drawings described below are merely some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0037] Figure 1 This is a surface SEM image of the silicon composite material in Example 1 of the present invention;

[0038] Figure 2 This is a surface SEM image of the silicon composite material in Comparative Example 1 of the present invention;

[0039] Figure 3 These are the first spectral distribution diagrams of the negative electrode sheet in Embodiment 1 and the negative electrode sheet in Comparative Example 1 of the present invention;

[0040] Figure 4 The images show the second spectral distribution of the negative electrode in Embodiment 1 and the negative electrode in Comparative Example 1 of this invention.

[0041] Figure 5 The third spectral distribution diagrams are shown for the negative electrode sheet in Embodiment 1 and the negative electrode sheet in Comparative Example 1 of the present invention.

[0042] Figure 6 This is a pore size distribution diagram of the silicon composite material in Example 1 of the present invention;

[0043] Figure 7 The above are EIS curves of the batteries in Embodiment 1 and Comparative Example 1 of the present invention. Detailed Implementation

[0044] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0045] A first aspect of the present invention provides a silicon composite material comprising liquid metal gallium and indium, wherein the sum of the mass percentages of gallium and indium in the silicon composite material is 0.05-0.2%, for example, the sum of the mass percentages of gallium and indium in the silicon composite material may be 0.05%, 0.07%, 0.09%, 0.1%, 0.12%, 0.14%, 0.16%, 0.18%, or 0.2%, etc.

[0046] The inventors discovered in their research that when the sum of the mass percentages of gallium and indium in the silicon composite material meets the aforementioned range, the negative electrode sheet containing this silicon composite material, when applied to a battery, can not only improve the battery's energy density but also form a stable SEI film. This negative electrode sheet exhibits excellent self-healing capabilities, improving the battery's initial efficiency and cycle performance. Too little gallium and indium will cause the SEI to crack, lose its repair ability, and decrease electrochemical performance; too much gallium and indium will reduce ED (excess energy density) and may even lead to short circuits.

[0047] Furthermore, based on the total mass of gallium and indium, the mass percentage of gallium is 68-74%, and the mass percentage of indium is 26-32%. For example, the mass percentage of gallium in gallium and indium can be 68%, and the mass percentage of indium can be 32%; or, the mass percentage of gallium in gallium and indium can be 69%, and the mass percentage of indium can be 31%; or, the mass percentage of gallium in gallium and indium can be 70%, and the mass percentage of indium can be 30%; or, the mass percentage of gallium in gallium and indium can be 71%, and the mass percentage of indium can be 29%; or, the mass percentage of gallium in gallium and indium can be 72%, and the mass percentage of indium can be 28%; or, the mass percentage of gallium in gallium and indium can be 73%, and the mass percentage of indium can be 27%; or, the mass percentage of gallium in gallium and indium can be 74%, and the mass percentage of indium can be 26%, etc. When the mass percentages of gallium and indium meet the above ranges, gallium and indium can be more fully matched, further improving the self-healing ability of the negative electrode and enhancing the cycle performance of the battery.

[0048] For example, the mass percentage of gallium and indium in silicon composite materials can be measured in the following way: a negative electrode sample of a certain size (e.g., 15mm × 15mm) is cut from a random area of ​​the negative electrode sheet. After wrapping the negative electrode sample with copper foil, the cross-section of the negative electrode sample is obtained by cutting it under freezing conditions (e.g., -80°C) using an ion beam polisher (e.g., Hitachi Arblade 5000). The negative electrode sample is sputtered with gold, and then the cross-section of the negative electrode sheet is obtained by scanning with a scanning electron microscope (e.g., Sigma 300 scanning electron microscope from ZEISS, Germany). Five silicon composite material particles are randomly selected from the image, and the mass percentage of gallium and indium in each particle is measured by energy dispersive spectroscopy (EDS). The average value is then calculated.

[0049] In some embodiments of the present invention, the silicon composite material includes a silicon core, an intermediate layer, and an outer layer; the intermediate layer is located on at least a portion of the surface of the silicon core, and the outer layer is located on at least a portion of the surface of the intermediate layer; the intermediate layer includes liquid metal (LM) gallium and indium, the outer layer includes metal-organic hybrid glass (MGs), and the silicon core is a micron-sized silicon material.

[0050] In the silicon composite material of the present invention, the intermediate layer may be located on a portion of the surface of the silicon core or on the entire outer surface of the silicon core; the outer layer may be located on a portion of the outer surface of the intermediate layer or on the entire outer surface of the intermediate layer. The silicon composite material of the present invention comprises, from the inside out, a silicon core, an intermediate layer, and an outer layer.

[0051] The intermediate layer includes liquid metal, which refers to a metal or alloy thereof that is liquid at room temperature or a lower heating temperature. For example, the liquid metal could be a liquid alloy formed by melting gallium and indium.

[0052] Metal-organic hybrid glasses are amorphous materials, also known as glassy MOFs. They are amorphous metal-organic framework materials formed by coordination bonds between metal ions or metal clusters and organic ligands. Glassy MOFs retain the porosity and short-range order of MOFs while exhibiting glass-like physical properties, such as mechanical stability and transparency.

[0053] Micron-sized silicon materials refer to silicon materials with a particle size of micrometers.

[0054] The silicon composite material of this invention uses liquid metal as a conductive buffer material. The liquid metal acts as a bridging agent, assembling a conductive metal-organic hybrid glass through coordination chemistry to encapsulate the silicon core. This silicon composite material possesses buffering and self-healing properties, effectively solving the problem of silicon composite materials breaking due to expansion during battery charging and discharging, thus leading to a decrease in battery cycle performance. Because this silicon composite material combines robust metal-organic hybrids (MGs) and deformable metal-organic hybrids (LMs), the battery can simultaneously achieve high rate capability and cycle stability. Furthermore, the polar and non-polar hierarchical pores of the MGs can adsorb carbon dioxide and hydrogen generated during battery cycling, reducing battery cycle thickness and further improving battery cycle performance.

[0055] In some embodiments of the present invention, the Dv50 of the silicon core is 5-30 μm. For example, the Dv50 of the silicon core can be 5 μm, 10 μm, 15 μm, 20 μm, 25 μm, or 30 μm. Preferably, the Dv50 of the silicon core is 20-30 μm. When the Dv50 of the silicon core meets the above range, the silicon core can more fully cover the intermediate layer and the outer layer, thereby improving the cycle performance of the battery.

[0056] In some embodiments of the present invention, the specific surface area of ​​the silicon composite material is 200-2000 m². 2 / g, for example, the specific surface area of ​​silicon composite materials can be 200m². 2 / g、300m 2 / g、400m 2 / g、500m 2 / g、600m 2 / g、700m 2 / g、800m 2 / g、900m 2 / g, 1000m 2 / g、1100m 2 / g、1200m 2 / g、1300m 2 / g, 1400m 2 / g, 1500m 2 / g, 1600m 2 / g、1700m 2 / g、1800m 2 / g、1900m 2 / g or 2000m 2 / g, etc. Preferably, the specific surface area of ​​the silicon composite material is 800-2000 m2 / g.

[0057] The specific surface area of ​​the silicon composite material is directly proportional to the specific surface area of ​​the pores in the MGs. The larger the specific surface area of ​​the pores in the MGs, the larger the specific surface area of ​​the silicon composite material. When the specific surface area of ​​the silicon composite material meets the above-mentioned range, the silicon composite material has a more sufficient contact area with the electrolyte when applied to batteries, which can improve the battery capacity.

[0058] In some embodiments of the present invention, the pore size of the silicon composite material is 1.3-2.7 nm. For example, the pore size of the silicon composite material can be 1.3 nm, 1.5 nm, 1.7 nm, 1.9 nm, 2.1 nm, 2.3 nm, 2.5 nm, or 2.7 nm, etc. When the pore size of the silicon composite material meets the above range, the formation of an SEI film in the pores of the silicon composite material can be avoided while ensuring the ionic conductivity of the silicon composite material, so that the battery has both excellent rate performance and cycle performance.

[0059] In some embodiments of the present invention, the Dv50 of the silicon composite material is 10-50 μm. For example, the Dv50 of the silicon composite material can be 10 μm, 15 μm, 20 μm, 25 μm, 30 μm, 35 μm, 40 μm, 45 μm, or 50 μm, etc. Preferably, the Dv50 of the silicon composite material is 35-50 μm. When the Dv50 of the silicon composite material meets the above range, when the silicon composite material is applied to a battery, it is not easily collapsed during the charging and discharging process of the battery, and it also has better lithium-ion intercalation / deintercalation performance.

[0060] In some embodiments of the present invention, the aspect ratio of the silicon composite material is 1-5. The aspect ratio refers to the ratio of the largest diameter dimension of the silicon composite material to the dimension perpendicular to the largest diameter. For example, the aspect ratio of the silicon composite material can be 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, or 5, etc. Preferably, the aspect ratio of the silicon composite material is 1-2. When the aspect ratio meets the above range, the rigidity of the negative electrode SEI film can be guaranteed, damage to the negative electrode SEI film can be avoided, and the cycle performance of the battery can be improved.

[0061] In some embodiments of the present invention, the CO2 adsorption enthalpy of the silicon composite material is 10-40 kJ / mol. For example, the CO2 adsorption enthalpy of the silicon composite material can be 10 kJ / mol, 15 kJ / mol, 20 kJ / mol, 25 kJ / mol, 30 kJ / mol, 35 kJ / mol, or 40 kJ / mol. Preferably, the CO2 adsorption enthalpy of the silicon composite material is 15-30 kJ / mol. When the CO2 adsorption enthalpy of the silicon composite material meets the above range, during the charging and discharging process of the battery, the silicon composite material can more fully adsorb the carbon dioxide and hydrogen generated during the charging and discharging process, avoiding an increase in battery thickness and further improving the cycle performance of the battery.

[0062] In some embodiments of the present invention, in the silicon composite material, the mass ratio of silicon core, metal-organic hybrid glass and liquid metal is (50-100):(5-20):1. For example, in silicon composite materials, the mass ratio of the silicon core, the metal-organic hybrid glass, and the liquid metal can be 50:5:1, 50:10:1, 50:15:1, 50:20:1, 60:5:1, 60:10:1, 60:15:1, 60:20:1, 70:5:1, 70:10:1, 70:15:1, 70:20:1, 80:5:1, 80:10:1, 80:15:1, 80:20:1, 90:5:1, 90:10:1, 90:15:1, 90:20:1, 100:5:1, 100:10:1, 100:15:1, or 100:20:1, etc. Preferably, in the silicon composite material, the mass ratio of the silicon core, metal-organic hybrid glass, and liquid metal is (70-90):(8-12):1. When the mass ratio of the silicon core, metal-organic hybrid glass, and liquid metal in the silicon composite material meets the above range, the silicon core, metal-organic hybrid glass, and liquid metal can be more fully matched, and the functions of the silicon core, metal-organic hybrid glass, and liquid metal can be fully utilized, resulting in a silicon composite material with both excellent energy density and self-healing ability, thereby improving the energy density and cycle performance of the battery.

[0063] In some embodiments of the present invention, the metal-organic hybrid glass comprises metal ions and ligands. The metal ions include at least one selected from copper ions, zinc ions, cobalt ions, iron ions, ferrous ions, zirconium ions, aluminum ions, and chromium ions. The ligands include at least one selected from 1,3,5-benzenetricarboxylic acid, 2'-amino-[1,1':4',1”-terphenyl]-4,4”-dicarboxylic acid, terephthalic acid, dimethylimidazole, 2,5-dimethylterephthalic acid, 2,5-diaminoterephthalic acid, and 2-amino-4,4'-biphenyldicarboxylic acid.

[0064] In some embodiments of the present invention, the micron-sized silicon material is at least one of micron-sized silicon carbide, micron-sized elemental silicon, micron-sized silicon oxide, micron-sized silicon nitride composite, and micron-sized silicon alloy.

[0065] A second aspect of the present invention provides a negative electrode sheet, comprising a negative electrode current collector and a negative electrode active layer located on at least one surface of the negative electrode current collector, the negative electrode active layer comprising a negative electrode active material, the negative electrode active material comprising the silicon composite material of the first aspect.

[0066] In this invention, the negative electrode active layer can be located on one surface or both surfaces of the negative electrode current collector. The negative electrode active material in the negative electrode active layer of this invention includes the silicon composite material of the first aspect, and the negative electrode active layer also includes a binder and a conductive agent.

[0067] The negative electrode of the present invention includes a silicon composite material as described in the first aspect, thus the negative electrode has excellent capacity and cycle performance, and when applied to a battery, it can improve the energy density and cycle performance of the battery.

[0068] In some embodiments of the present invention, the mass percentage of silicon composite material in the negative electrode active layer is 2-50%, for example, the mass percentage of silicon composite material can be 2%, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, or 50%, etc. When the mass percentage of silicon composite material in the negative electrode active layer meets the above range, the role of silicon composite material can be fully utilized, improving the energy density and cycle performance of the battery.

[0069] In some embodiments of the present invention, the sum of the mass percentages of gallium and indium in the negative electrode active layer is 0.01-0.04%, for example, the sum of the mass percentages of gallium and indium in the negative electrode active layer can be 0.01%, 0.02%, 0.03%, or 0.04%. Preferably, the mass percentages of silicon, gallium, and indium in the negative electrode active layer can be (1-1.8):(0.0136-0.0148):(0.0052-0.0064). When the sum of the mass percentages of gallium and indium in the negative electrode active layer meets the above range, the negative electrode sheet including this negative electrode active layer, when applied to a battery, can not only improve the energy density of the battery, but also form a stable SEI film. This negative electrode sheet has excellent self-healing ability and can improve the cycle performance of the battery.

[0070] In some embodiments of the present invention, in the color spectrum of the negative electrode, the ratio of peak height to peak width is greater than 40:1, for example, the ratio is 50:1, 60:1, 70:1, 80:1, or 90:1. A ratio greater than 40:1 in the color spectrum of the negative electrode indicates that the silicon composite material (i.e., the active material) in the negative electrode of the present invention is densely packed. This dense packing of silicon composite material can, on the one hand, improve the powder shedding of the active layer of the negative electrode caused by silicon expansion, and on the other hand, improve the uniformity of the SEI film on the surface of the negative electrode, thereby enhancing the stability and kinetic performance of the negative electrode, and ultimately improving the cycle capacity retention, furnace temperature performance, and rate performance of the battery.

[0071] In this invention, the color spectrum of the negative electrode can be analyzed by comparing the spectral distribution of the negative electrode of this invention with that of other negative electrodes in different channels (e.g., red, green, and blue) using SEM images of the negative electrode of this invention and other negative electrodes. The spectral distribution describes the frequency of each intensity value in the image and is an important indicator of the statistical characteristics of the image. Specifically, it includes: 1. Image acquisition and preprocessing: importing the SEM images of the negative electrode of this invention and other negative electrodes for processing. Each SEM image can be regarded as a three-dimensional matrix composed of multiple channels, and each channel represents a specific wavelength (e.g., RGB channel); 2. Spectral distribution calculation: calculating the spectral distribution for each channel of each SEM image. The spectral distribution represents the frequency of each pixel intensity value (from 0 to 255) in the image. The spectral distribution can be obtained by calculating the histogram of the image; 3. Spectral comparison analysis: comparing the spectral distribution of two SEM images in the same channel. By plotting the spectral distribution in the same coordinate system, the differences between the two images at different intensity values ​​can be observed intuitively. During the comparison, by comparing the frequency of each intensity value, the similarity and differences of images in specific channels can be determined. Analyzing the spectral comparison charts explains the differences in spectral distribution between the two images in different channels. Through this comparison, conclusions can be drawn regarding material composition, structural characteristics, etc. Specifically, the horizontal axis (X-axis) represents the pixel intensity value of the image; for each color channel, these values ​​range from 0 to 255, where 0 represents the darkest and 255 represents the brightest. The vertical axis (Y-axis) represents the frequency of occurrence of that pixel intensity value; this is the number of times each pixel intensity value appears in the image.

[0072] A third aspect of the present invention provides a battery comprising the negative electrode of the second aspect.

[0073] It is understood that a battery also includes a positive electrode, a separator, an electrolyte, and an outer packaging. In this invention, the positive electrode, separator, and negative electrode can be stacked to form a stacked electrode assembly, then the electrode assembly is placed in the outer packaging, electrolyte is injected into the outer packaging, and after sealing and formation, a battery is formed; alternatively, the positive electrode, separator, and negative electrode can be stacked and wound to form a wound electrode assembly, then the electrode assembly is placed in the outer packaging, electrolyte is injected into the outer packaging, and after sealing and formation, a battery is formed.

[0074] The battery of the present invention, due to including the negative electrode sheet of the second aspect, has excellent cycle performance and energy density.

[0075] In some embodiments of the present invention, the electrolyte includes lithium hexafluorophosphate, and the concentration of lithium hexafluorophosphate in the electrolyte is c, mol / L; in the negative electrode, the mass percentage w of the silicon composite material satisfies w:c = (10-30):1, for example, w:c can be equal to 10:1, 15:1, 20:1, 25:1 or 30:1, etc. Preferably, w:c = (15-25):1. When w:c meets the above range, during the charging and discharging process of the battery, the negative electrode including the silicon composite material is not easily expanded, and has excellent electrolyte wettability, which helps to improve the cycle performance and rate performance of the battery.

[0076] The inventors also discovered in their research that when the ohmic impedance of the battery of this invention is <34mΩ, the membrane impedance is <13mΩ, and the charge transfer impedance is <30mΩ, the battery exhibits superior rate performance. Here, ohmic impedance represents the fundamental resistance inside the battery, affecting its energy efficiency and heat generation, and is typically measured using high-frequency impedance analysis. Membrane impedance mainly refers to the impedance of the SEI film on the surface of the negative electrode, reflecting the ease with which lithium ions pass through the SEI film, and is usually observed in the mid-frequency range. Charge transfer impedance refers to the charge transfer impedance at the negative electrode / electrolyte interface, reflecting the kinetic characteristics of the electrochemical reaction, and is typically represented as a semi-circular arc in the impedance spectrum in the low-to-mid-frequency region.

[0077] Furthermore, the battery has an ohmic impedance of <33mΩ, a membrane impedance of <12.5mΩ, and a charge transfer impedance of <20mΩ.

[0078] The technical solution of the present invention will be further described below with reference to specific embodiments.

[0079] Example 1

[0080] The battery in this embodiment is prepared by a method including the following steps:

[0081] 1) Preparation of silicon composite materials

[0082] a. Preparation of MGs

[0083] Copper nitrate (Cu(NO3)2), zinc nitrate (Zn(NO3)2), cobalt nitrate (Co(NO3)2), 1,3,5-benzenetricarboxylic acid (BTC), and 2'-amino-[1,1':4',1”-terphenyl]-4,4”-dicarboxylic acid (amino-TPDC) were added to a ball mill in a molar ratio of 5:2:4:4:2. Appropriate milling media (such as stainless steel balls, ceramic balls, etc.) were then added for ball milling. The milled product was then removed from the mill jar and washed with DMF to remove unreacted precursors and byproducts. The solid product was then separated by filtration and dried in a vacuum drying oven at 120°C for 12 hours to obtain MGs.

[0084] The grinding media consisted of zirconia balls with a diameter of 2-8 mm. The ball-to-material ratio was 5:1, the rotation speed was 400 rpm, and the grinding time was 10 h.

[0085] b. Preparation of LM

[0086] In an argon atmosphere, 71 wt% gallium and 29 wt% indium were melted to form a liquid alloy; 200 mg of the liquid alloy was added to 2 mL of deionized water and ultrasonically treated with a probe to form an LM suspension with a concentration of 100 mg / mL.

[0087] c. Preparation of silicon composite materials

[0088] mSi particles and MGs powder were added to LM suspension (mass ratio of the three 80:10:1) to obtain silicon composite material LM-MGs-mSi powder, which includes silicon core, LM and MGs from the inside out.

[0089] 2) Preparation of negative electrode sheet

[0090] LM-MGs-mSi, artificial graphite, conductive carbon black (SP) and styrene-butadiene rubber (SBR) were mixed in a mass ratio of 2:6:1:1, deionized water was added, and the negative electrode active slurry was obtained under the action of a vacuum mixer.

[0091] The negative electrode active slurry was uniformly coated on both surfaces of an 8μm thick copper foil, then air-dried at room temperature, and then transferred to a 60℃ oven for 24 hours. After cold pressing and slitting, a negative electrode sheet including the negative electrode active layer was obtained.

[0092] 3) Preparation of positive electrode sheet

[0093] Lithium cobalt oxide (LiCoO2), polyvinylidene fluoride (PVDF), and conductive carbon black (super P) were mixed in a mass ratio of 7:1:2. N-methylpyrrolidone (NMP) was added, and the mixture was stirred under vacuum to form a uniform and fluid positive electrode active slurry.

[0094] The positive electrode active slurry was uniformly coated on both surfaces of a 10μm thick aluminum foil, dried in an oven at 60℃ for 24h, and then rolled and slit to obtain a positive electrode sheet including the positive electrode active layer.

[0095] 4) Preparation of electrolyte

[0096] In an argon-filled glove box (H2O < 0.1 ppm, O2 < 0.1 ppm), EC and DMC are mixed evenly at a volume ratio of 1:1, and then fully dried lithium hexafluorophosphate (LiPF6) is quickly added to form an electrolyte with a concentration of 1 mol / L.

[0097] 5) Battery manufacturing

[0098] After stacking the positive electrode sheet from step 3), the negative electrode sheet from step 2), and the separator in the order of positive electrode sheet, separator, and negative electrode sheet, the electrode assembly is then wound to obtain an electrode assembly. The electrode assembly is placed in an outer packaging aluminum foil, and the electrolyte from step 4) is injected into the outer packaging aluminum foil. After vacuum sealing, settling, formation, shaping, and sorting processes, a battery is obtained.

[0099] The specific parameters of the battery are shown in Table 1 and Table 2.

[0100] The preparation methods of Examples 2-35 are basically the same as those of Example 1, with the differences shown in Table 1.

[0101] Comparative Example 1

[0102] The preparation method of the battery in this comparative example is basically the same as that in Example 1, except that:

[0103] Use mSi to replace silicon composite materials.

[0104] Comparative Example 2

[0105] The preparation method of the battery in this comparative example is basically the same as that in Example 1, except that:

[0106] 1) Preparation of silicon composite materials

[0107] a. Preparation of MOFs

[0108] HKUST-1 and Zn-BTC powders were physically mixed (all materials were commercially purchased) to form MOFs, in which the molar ratio of HKUST-1 to Zn-BTC was 5:2.

[0109] c. Preparation of silicon composite materials

[0110] By replacing MGs with MOFs, a silicon composite material LM-MOFs-mSi powder is formed.

[0111] Performance testing

[0112] The silicon composite materials and batteries in the examples and comparative examples were subjected to the following performance tests, and the results are shown in Table 1 and Table 2.

[0113] 1. SEM testing

[0114] Surface SEM images of the negative electrode sheets in Example 1 and Comparative Example 1 were obtained respectively. Figure 1 This is a surface SEM image of the negative electrode sheet in Embodiment 1 of the present invention; Figure 2 This is a surface SEM image of the negative electrode sheet in Comparative Example 1 of the present invention. From... Figure 1 and Figure 2 As can be seen, compared with Comparative Example 1, the surface morphology of the negative electrode sheet in Example 1 is more complete. When the negative electrode sheet is applied to the battery, it is not easy to break during the charging and discharging process of the battery, which is beneficial to the cycle performance of the battery.

[0115] 2. Color spectrum characteristics

[0116] 1) Image Acquisition and Preprocessing: The SEM images of the negative electrode from Example 1 and Comparative Example 1 are imported and processed. Each SEM image can be viewed as a three-dimensional matrix composed of multiple channels, with each channel representing a specific wavelength (e.g., RGB channels). 2) Spectral Distribution Calculation: The spectral distribution is calculated for each channel of each SEM image. The spectral distribution represents the frequency of each pixel intensity value (from 0 to 255) in the image. The spectral distribution is obtained by calculating the image histogram. 3) Spectral Comparison Analysis: The spectral distributions of the two SEM images in the same channels are compared. By plotting the spectral distributions on the same coordinate system, the differences between the two images at different intensity values ​​can be visually observed. During the comparison, the similarity and differences of the images in specific channels can be determined by comparing the frequency of each intensity value. The spectral comparison chart is analyzed to explain the differences in spectral distributions of the two images in different channels. Through this comparison, conclusions regarding material composition, structural characteristics, etc., can be drawn. The horizontal axis (X-axis) represents the pixel intensity value of the image. For each color channel, these values ​​range from 0 to 255, where 0 represents the darkest and 255 represents the brightest. The vertical axis (Y-axis) represents the frequency of the pixel intensity value, which is the number of times each pixel intensity value appears in the image.

[0117] Figure 3 These are the first spectral distribution diagrams of the negative electrode sheet in Embodiment 1 and the negative electrode sheet in Comparative Example 1 of the present invention; Figure 4 The images show the second spectral distribution of the negative electrode in Embodiment 1 and the negative electrode in Comparative Example 1 of this invention. Figure 5This is a third type of spectral distribution diagram for the negative electrode sheet in Embodiment 1 and Comparative Example 1 of the present invention. Figure 3-5 As can be seen, the spectral curve peak in Example 1 is relatively high, indicating that the integrity of the negative electrode sheet in Example 1 is just right. When applied to the battery, it is not easy to break, which helps to improve the cycle performance of the battery.

[0118] 3. Specific surface area (BET) and pore size distribution of silicon composite materials

[0119] Sample pretreatment conditions: Temperature: 150℃ to 200℃; Time: 6 to 12 hours; Vacuum: <10^ -5 Torr;

[0120] Nitrogen adsorption experimental conditions: Adsorbed gas: nitrogen (N2); Temperature: 77K (liquid nitrogen temperature); Pressure range: 0.01 to 1.0 relative pressure (P / P0); Number of adsorption isotherm points: 30 to 50 points, covering the low-pressure to high-pressure region;

[0121] Data analysis method: BET: obtained by linear fitting within a relative pressure range of 0.05 to 0.3;

[0122] Pore ​​size distribution calculation: The pore size distribution was extracted from the adsorption or desorption branches using the BJH (Barrett-Joyner-Halenda) method.

[0123] Figure 6 This is a pore size distribution diagram of the silicon composite material in Example 1 of the present invention. From... Figure 6 It can be seen that the pore size distribution of the silicon composite material in Example 1 is 1.3-2.7 nm.

[0124] 4. CO2 adsorption enthalpy

[0125] Multi-temperature adsorption experimental conditions: Adsorbed gas: carbon dioxide (CO2); Temperature range: 273K, 298K and 323K; Pressure range: 0 to 1 bar; Number of adsorption isotherm points: at least 15 points at each temperature, covering the low-pressure to high-pressure region;

[0126] Pretreatment conditions: Temperature: Same as nitrogen adsorption pretreatment temperature; Time: 6 to 12 hours; Vacuum: <10^ -5 Torr;

[0127] Adsorption enthalpy calculation method: Clausius-Clapeyron equation: Adsorption enthalpy is calculated using the pressure values ​​of the same adsorption amount at different temperatures and the Clausius-Clapeyron equation.

[0128] Fitting method: Linear fitting of data to determine enthalpy value.

[0129] 5. Indium and gallium content

[0130] The negative electrode active layer in the negative electrode sheets of the examples and comparative examples was scraped off, dissolved in aqua regia (a mixture of HCl and HNO3), diluted, and then measured by ICP.

[0131] 6. EIS

[0132] Equipment: Electrochemical workstation

[0133] Method: Connect the positive and negative electrodes of the battery to the working electrode (WE) and the counter electrode (CE), respectively. Measure the frequency range from 0.01 Hz to 1 MHz. AC voltage amplitude: 5 mV or 10 mV.

[0134] Figure 7 The images show the EIS curves of the batteries in Embodiment 1 and Comparative Example 1 of the present invention. Figure 7 It can be seen that the film impedance and charge transfer impedance of the battery in the embodiment of the present invention are significantly smaller than those of the battery in Comparative Example 1, indicating that the composite silicon material of the present invention can form an SEI film with lower impedance at the negative electrode.

[0135] 7. Capacity retention rate and thickness expansion rate

[0136] The battery was kept at 25℃ for 30 minutes, then charged at a constant current (XC, see Table 1 for details) to 4.53V, followed by constant voltage charging at 4.53V, with a cutoff at 0.3C; and discharged at 0.7C to 3V. This charging regime was followed for 200 charging cycles, and the capacity retention rate was calculated.

[0137] Measure the initial fully charged thickness P0 and the fully charged thickness P after cycling, and calculate the thickness expansion rate = (P-P0) / P0×100%.

[0138] 8. First effect

[0139] The battery was kept at 25℃ for 30 minutes, then charged at a constant current (XC, see Table 1 for details) to 4.53V, followed by constant voltage charging at 4.53V, with a cutoff at 0.3C; and discharged at 0.7C to 3V. The initial efficiency was calculated as (initial discharge capacity / initial charge capacity) × 100%.

[0140] It should be noted that the test conditions of the multiple embodiments and comparative examples are basically the same. The only difference is that the multiplier of Embodiments 2 and 3 is different from that of the other embodiments.

[0141] Table 1

[0142]

[0143]

[0144] In Table 1, pore size refers to the maximum value within the pore size distribution range; In+Ga refers to the sum of the mass percentages of gallium and indium in the negative electrode active layer.

[0145] Table 2

[0146]

[0147] As can be seen from Table 2, the battery in the embodiment of the present invention has lower ohmic impedance, dielectric impedance and charge transfer impedance. The battery has better first-efficiency, capacity retention and lower thickness expansion rate, indicating that when the silicon composite material of the present invention is applied to the battery, it can reduce the battery impedance and improve the battery's first-efficiency and cycle performance.

[0148] Furthermore, as can be seen from Examples 1, 4 to 7, by selecting the Dv50 of the silicon core of the silicon composite material, the impedance of the battery can be further reduced, the initial efficiency and capacity retention rate of the battery can be improved, and the thickness expansion rate of the battery can be reduced.

[0149] As can be seen from Examples 1, 8, and 9, by making the BET of the silicon composite material satisfy 200-2000m... 2 / g, the obtained battery has lower impedance and thickness expansion rate, and better first-time efficiency and capacity retention; as can be seen from Examples 1 and 9, when the BET of the silicon composite material meets 800-2000m 2 At / g, it can further improve the battery's initial efficiency and capacity retention, and reduce the battery's impedance and thickness expansion rate.

[0150] As can be seen from Examples 1 and 10, by selecting the pore size of the silicon composite material, the impedance of the battery can be further reduced, the initial efficiency and capacity retention of the battery can be improved, and the thickness expansion rate of the battery can be reduced.

[0151] As can be seen from Examples 1, 12 to 16, by selecting the Dv50 of the silicon composite material, the impedance of the battery can be further reduced, the first-time efficiency and capacity retention rate of the battery can be improved, and the thickness expansion rate of the battery can be reduced. As can be seen from Examples 12 to 15, when the Dv50 of the silicon composite material is 35-50μm, the obtained battery has better first-time efficiency and capacity retention rate, and lower thickness expansion rate and impedance.

[0152] As can be seen from Examples 1, 17 and 18, when the aspect ratio of the silicon composite material is 1-5, the obtained battery has better first-time efficiency, capacity retention rate and lower impedance and thickness expansion rate; as can be seen from Examples 1 and 17, when the aspect ratio of the silicon composite material is 1-2, the obtained battery has better first-time efficiency, capacity retention rate and lower impedance and thickness expansion rate.

[0153] As can be seen from Examples 1, 20 to 23, by selecting the content of indium and gallium in the total mass of indium and gallium, the initial efficiency and capacity retention of the battery can be improved, while the impedance and thickness expansion rate of the battery can be reduced.

[0154] As can be seen from Examples 1 and 30, by selecting the content of silicon composite material in the negative electrode sheet, the ratio of the content of silicon composite material in the negative electrode sheet to the concentration of lithium hexafluorophosphate in the electrolyte can be optimized, further improving the battery's initial efficiency and capacity retention rate, and reducing the battery's impedance and thickness expansion rate. As can be seen from Examples 1, 24 to 29, when the mass percentage content of silicon composite material in the negative electrode sheet to the concentration of lithium hexafluorophosphate in the electrolyte is (10-30):1, the obtained battery has lower impedance and thickness expansion rate, and higher initial efficiency and capacity retention rate. As can be seen from Examples 1, 24 to 28, when the mass percentage content of silicon composite material in the negative electrode sheet to the concentration of lithium hexafluorophosphate in the electrolyte is (15-25):1, the obtained battery has lower impedance and thickness expansion rate, and higher initial efficiency and capacity retention rate.

[0155] As can be seen from Examples 1, 31 to 33, by selecting the content of the sum of the mass percentages of indium and gallium in the negative electrode active layer, the initial efficiency and capacity retention of the battery can be improved, while the impedance and thickness expansion rate of the battery can be reduced.

[0156] As can be seen from Examples 1 and 34, by selecting the mass ratio of silicon core, metal-organic hybrid glass and liquid metal in silicon composite material, the sum of the mass percentages of indium and gallium in silicon composite material can be optimized, thereby improving the first efficiency and capacity retention of the battery, and reducing the impedance and thickness expansion rate of the battery.

[0157] The various embodiments in this specification are described in a related manner. Similar or identical parts between embodiments can be referred to interchangeably. Each embodiment focuses on its differences from other embodiments. The above are merely preferred embodiments of the present invention and are not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention are included within the scope of protection of the present invention.

Claims

1. A silicon composite material, characterized in that, The silicon composite material includes a silicon core, an intermediate layer, and an outer layer; The intermediate layer is located on at least a portion of the surface of the silicon core, and the outer layer is located on at least a portion of the surface of the intermediate layer; The intermediate layer comprises liquid gallium and indium, and the total mass percentage of gallium and indium in the silicon composite material is 0.05-0.2%. The outer layer comprises a metal-organic hybrid glass, and the silicon core is a micron-sized silicon material.

2. The silicon composite material according to claim 1, characterized in that, Based on the total mass of gallium and indium, the mass percentage of gallium is 68-74%, and the mass percentage of indium is 26-32%.

3. The silicon composite material according to claim 1, characterized in that, The Dv50 of the silicon core is 5-30μm.

4. The silicon composite material according to claim 3, characterized in that, The Dv50 of the silicon core is 20-30μm.

5. The silicon composite material according to claim 1, 3, or 4, characterized in that, The specific surface area of ​​the silicon composite material is 200-2000 m². 2 / g; and / or, The silicon composite material has a pore size of 1.3-2.7 nm; and / or, The Dv50 of the silicon composite material is 10-50 μm; and / or, The aspect ratio of the silicon composite material is 1-5; and / or, The CO2 adsorption enthalpy of the silicon composite material is 10-40 kJ / mol.

6. The silicon composite material according to claim 5, characterized in that, The specific surface area of ​​the silicon composite material is 800-2000 m². 2 / g; and / or, The silicon composite material has a Dv50 of 35-50 μm; and / or, The aspect ratio of the silicon composite material is 1-2; and / or, The CO2 adsorption enthalpy of the silicon composite material is 15-30 kJ / mol.

7. The silicon composite material according to claim 1, characterized in that, In the silicon composite material, the mass ratio of silicon core, metal-organic hybrid glass and liquid metal is (50-100):(5-20):

1.

8. The silicon composite material according to claim 7, characterized in that, In the silicon composite material, the mass ratio of silicon core, metal-organic hybrid glass and liquid metal is (70-90):(8-12):

1.

9. The silicon composite material according to claim 1, characterized in that, The metal-organic hybrid glass comprises metal ions and ligands, wherein the metal ions include at least one selected from copper ions, zinc ions, cobalt ions, iron ions, ferrous ions, zirconium ions, aluminum ions, and chromium ions, and the ligands include at least one selected from 1,3,5-benzenetricarboxylic acid, 2'-amino-[1,1':4',1''-terphenyl]-4,4''-dicarboxylic acid, terephthalic acid, dimethylimidazole, 2,5-dimethylterephthalic acid, 2,5-diaminoterephthalic acid, and 2-amino-4,4'-biphenyldicarboxylic acid; And / or, the micron-sized silicon material is at least one of micron-sized silicon carbide, micron-sized elemental silicon, micron-sized silicon oxide, micron-sized silicon nitride composite, and micron-sized silicon alloy.

10. A negative electrode sheet, characterized in that, It includes a negative electrode current collector and a negative electrode active layer located on at least one surface of the negative electrode current collector, the negative electrode active layer comprising a negative electrode active material, the negative electrode active material comprising the silicon composite material according to any one of claims 1-9.

11. The negative electrode sheet according to claim 10, characterized in that, In the negative electrode active layer, the mass percentage of the silicon composite material is 2-50%; And / or, the sum of the mass percentages of gallium and indium is 0.01-0.04%.

12. The negative electrode sheet according to claim 11, characterized in that, In the negative electrode active layer, the mass percentages of silicon, gallium, and indium are (1-1.8):(0.0136-0.0148):(0.0052-0.0064).

13. The negative electrode sheet according to any one of claims 10-12, characterized in that, In the color spectrum of the negative electrode, the ratio of peak height to peak width at the bottom is greater than 40:

1.

14. A battery, characterized in that, Includes the negative electrode sheet as described in any one of claims 10-12.

15. The battery according to claim 14, characterized in that, It also includes an electrolyte comprising lithium hexafluorophosphate, wherein the concentration of lithium hexafluorophosphate in the electrolyte is c, mol / L; and in the negative electrode, the mass percentage w of the silicon composite material satisfies: w:c=(10-30):

1.

16. The battery according to claim 15, characterized in that, w:c=(15-25):

1.

17. The battery according to claim 14, characterized in that, The battery has an ohmic impedance of <34mΩ, a membrane impedance of <13mΩ, and a charge transfer impedance of <30mΩ.

18. The battery according to claim 17, characterized in that, The battery has an ohmic impedance of <33mΩ, a membrane impedance of <12.5mΩ, and a charge transfer impedance of <20mΩ.

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