Negative electrode material and battery

Abstract

Provided in the present application are a negative electrode material and a battery. The negative electrode material comprises a carbon matrix and active particles, wherein the active particles comprise a silicon material, and at least part of the silicon material is distributed in the carbon matrix. The negative electrode material satisfies 1<γ≤2.2, wherein γ=I / q, I represents the maximum value of a delithiation peak value in the range of 0.4 V to 0.5 V in the differential capacity (dQ / dV) curve of a three-electrode battery made of the negative electrode material, and q represents the initial charge specific capacity of a button battery made of the negative electrode material at a voltage of 1.5 V. The negative electrode material and the battery provided in the present application have a relatively high specific capacity, high initial Coulombic efficiency and good cycle performance.

Description

Anode materials and batteries

[0001] Cross-reference to related applications

[0002] This application claims priority to Chinese Patent Application No. 202411943378.5, filed on December 24, 2024, entitled “Anode Material and Battery”, the entire contents of which are incorporated herein by reference. Technical Field

[0003] This application belongs to the field of negative electrode material technology, and more specifically, relates to negative electrode materials and batteries. Background Technology

[0004] In recent years, with market development, the integration and increasing functionality of power devices, and the growing demand for energy supply, lithium-ion batteries are widely used not only in mobile devices such as smartphones and laptops, but also in electric vehicles and power tools. Developing lithium-ion batteries with higher energy density is the current trend. The positive and negative electrode materials are the core of the battery, determining its operating efficiency. Currently, the commercially available negative electrode material is graphite, whose capacity is nearing its theoretical limit, with limited room for further improvement. Therefore, there is an urgent need to develop a new generation of high-energy-density negative electrode materials.

[0005] Silicon anodes are widely considered the next-generation battery anode material, possessing advantages such as high capacity, abundant supply, and relative safety. However, silicon anodes exhibit a severe volume expansion effect during cycling, leading to material pulverization, breakage, and rapid cycle degradation. To address this issue, multiple solutions exist, including structural design of silicon and composite coating using nanotechnology and porous techniques.

[0006] However, the volume expansion of silicon still affects the cycle performance and capacity utilization of the anode material, and there is still much room for improvement. Summary of the Invention

[0007] This application provides a negative electrode material and a battery that can improve the capacity, initial coulombic efficiency and cycle performance of the negative electrode material.

[0008] In a first aspect, this application provides an anode material, comprising a carbon matrix and active particles, wherein the active particles comprise silicon material, and at least a portion of the silicon material is distributed within the carbon matrix.

[0009] The negative electrode material satisfies 1 < γ ≤ 2.2, γ = I / q, IμAh / V represents the maximum value of the delithiation peak in the voltage-capacity differential dQ / dV curve of the three-electrode battery made of the negative electrode material in the range of 0.4V to 0.5V, q mAh / g represents the initial charge specific capacity of the coin cell made of the negative electrode material at 1.5V, and the unit of γ is 10. -3 g / V.

[0010] This application provides a battery comprising the negative electrode material described in the first aspect.

[0011] The technical solution of this application has at least the following beneficial effects:

[0012] The initial charge specific capacity q of the negative electrode material provided in this application can characterize the total silicon content in the negative electrode material. For a negative electrode material with the same silicon content, the more exposed silicon material, the more intense the side reactions between the silicon material and the electrolyte, leading to increased consumption of active lithium ions. A thicker solid electrolyte interface film on the surface of the negative electrode material also affects the lithium ion insertion / extraction efficiency, and the lithium extraction peak I will increase accordingly. If the exposed silicon content in the negative electrode material is too high, the side reactions with the electrolyte will intensify, the initial coulombic efficiency will decrease, and the cycle performance of the negative electrode material will also decline. In this application, the exposed silicon material in the negative electrode material is difficult to characterize directly. Through extensive research, the applicant has discovered that the content of exposed silicon material on the surface of the negative electrode material particles can be characterized by controlling the ratio of the lithium extraction peak I to the initial charge specific capacity q. Extensive research has revealed that when 1 < γ ≤ 2.2, most of the silicon material is uniformly distributed within the carbon matrix, which can improve the specific capacity of the anode material. At the same time, since most of the silicon material is distributed inside the carbon matrix, the side reactions between the anode material and the electrolyte are reduced during the first charge and discharge process, and the irreversible loss of active lithium ions is reduced. This allows the anode material to have both high specific capacity, high initial coulombic efficiency, and excellent cycle performance. Attached Figure Description

[0013] The present application will be further described below with reference to the accompanying drawings and embodiments.

[0014] Figure 1 is a schematic diagram of the discharge state of the battery provided in an embodiment of this application.

[0015] Figure 2 is a scanning electron microscope (SEM) image of the negative electrode material prepared in Example 4 of this application.

[0016] Figure 3 is the XRD pattern of the negative electrode material prepared in Example 4 of this application.

[0017] Figure 4 shows the first charge-discharge curve of the negative electrode material prepared in Example 4 of this application.

[0018] Figure 5 is a schematic diagram of the cycle performance curve of the negative electrode material prepared in Example 4 of this application.

[0019] Figure 6 shows the voltage-capacity differential dQ / dV curve of the negative electrode material prepared in Example 4 of this application. Detailed Implementation

[0020] To better understand the technical solution of this application, the embodiments of this application will be described in detail below with reference to the accompanying drawings.

[0021] It should be understood that the described embodiments are merely some, not all, of the embodiments in this application. All other embodiments obtained by those skilled in the art based on the embodiments in this application without inventive effort are within the scope of protection of this application.

[0022] The terminology used in the embodiments of this application is for the purpose of describing particular embodiments only and is not intended to be limiting of this application. The singular forms “a,” “the,” and “the” used in the embodiments of this application and the appended claims are also intended to include the plural forms unless the context clearly indicates otherwise.

[0023] It should be understood that the term "and / or" used in this article is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, and B existing alone. Additionally, the character " / " in this article generally indicates that the preceding and following related objects have an "or" relationship.

[0024] The negative electrode material provided in this application includes a carbon matrix and active particles. The active particles include silicon material, and at least a portion of the silicon material is distributed within the carbon matrix.

[0025] The negative electrode material satisfies 1 < γ ≤ 2.2, γ = I / q, I μAh / V represents the delithiation peak value in the 0.4V to 0.5V range in the voltage-capacity differential dQ / dV curve of the three-electrode battery made of the negative electrode material, and Q mAh / g represents the initial charge specific capacity of the coin cell made of the negative electrode material at 1.5V. The unit of γ is 10-1. -3 g / V.

[0026] The initial charge specific capacity q of the negative electrode material provided in this application can characterize the total silicon content in the negative electrode material. For a negative electrode material with the same silicon content, the more exposed silicon material, the more intense the side reactions between the silicon material and the electrolyte, leading to increased consumption of active lithium ions. A thicker solid electrolyte interface film on the surface of the negative electrode material also affects the lithium ion insertion / extraction efficiency, and the lithium extraction peak I will increase accordingly. If the exposed silicon content in the negative electrode material is too high, the side reactions with the electrolyte will intensify, the initial coulombic efficiency will decrease, and the cycle performance of the negative electrode material will also decline. In this application, the exposed silicon material in the negative electrode material is difficult to characterize directly. Through extensive research, the applicant has discovered that the content of exposed silicon material on the surface of the negative electrode material particles can be characterized by controlling the ratio of the lithium extraction peak I to the initial charge specific capacity q. Extensive research has revealed that when 1 < γ ≤ 2.2, most of the silicon material is uniformly distributed within the carbon matrix, which can improve the specific capacity of the anode material. At the same time, since most of the silicon material is distributed inside the carbon matrix, the side reactions between the anode material and the electrolyte are reduced during the first charge and discharge process, and the irreversible loss of active lithium ions is reduced. This allows the anode material to have both high specific capacity, high initial coulombic efficiency, and excellent cycle performance.

[0027] In some embodiments, the negative electrode material satisfies 1 < γ ≤ 2.2, where γ can specifically be 2.2, 2.18, 2.14, 2.11, 2.1, 2.09, 2.05, 2.03, 2.0, 1.95, 1.87, 1.8, 1.79, 1.6, 1.5, 1.4, 1.2, 1.15, or 1.1, or other values ​​within the above range, which are not limited here. When the γ ratio is too large, the amount of exposed silicon material on the surface of the negative electrode material increases, leading to an aggravation of the side reactions between the negative electrode material and the electrolyte. The thickness of the solid electrolyte interphase (SEI) film on the surface of the negative electrode material becomes too large. A thicker SEI film increases the resistance to lithium-ion transport and also leads to a decrease in the cycle performance of the battery prepared with the negative electrode material, especially rapid degradation during high-temperature cycling.

[0028] In some embodiments, the negative electrode material satisfies 1000 ≤ q ≤ 3300, where q can specifically be 1000, 1300, 1500, 1800, 2000, 2200, 2400, 2600, 2800, 3000, or 3300, or other values ​​within the above range, and is not limited here. A q value below 1000 indicates a low capacity of the negative electrode material, which is detrimental to improving battery energy density; a q value above 3300 indicates an excessively high silicon content in the negative electrode material, resulting in a correspondingly low carbon content and a risk of significant silicon exposure, leading to poor cycle stability of the negative electrode material.

[0029] In some embodiments, the negative electrode material satisfies 2000≤I≤6600, where I can specifically be 2000, 2500, 2900, 3000, 3100, 3300, 3500, 3700, 4000, 4300, 4500, 4800, 5200, 5500, 5900, 6200, 6400, or 6600, or other values ​​within the above range, without limitation. If the I value is too low, it indicates that there is less silicon material deposited in the carbon matrix, resulting in a lower energy density of the negative electrode material; if the I value is too high, it indicates that the possibility of silicon floating on the surface of the negative electrode material increases significantly, which is detrimental to the cycle stability of the negative electrode material.

[0030] In some embodiments, the volumetric particle size distribution width P of the negative electrode material is equal to (D 90 -D 10 ) / (D 50 +D 10 The p-value is defined as follows: 0.1 ≤ P ≤ 1.4. Specifically, it can be 0.1, 0.15, 0.2, 0.3, 0.5, 0.6, 0.72, 0.8, 0.95, 1.0, 1.1, 1.2, 1.24, 1.24, 1.3, 1.34, 1.35, 1.38, 1.39, or 1.4, or other values ​​within the above range. When P is greater than 1.4, the particle size distribution of the negative electrode material is too wide, resulting in poor particle size uniformity, decreased uniformity of silicon distribution, increased side reactions between the negative electrode material and the electrolyte, and a decrease in the initial coulombic efficiency of the negative electrode material. When P is less than 0.1, the particle size distribution of the negative electrode material is too narrow, leading to a decrease in tap density and energy density. Studies have shown that excessive fine powder can lead to the continuous consumption of electrolyte by highly active battery materials during cycling, resulting in a deterioration in capacity retention. Larger particles with greater expansion are prone to pulverization during cycling, which can lead to a continuous thickening of the SEI (Sediment Intercalation / Deintercalation) and make lithium insertion / extraction in silicon materials more difficult. Therefore, narrowing the particle size distribution of the anode material can improve its cycle performance.

[0031] In some embodiments, the carbon matrix includes at least one of hard carbon, soft carbon, and mesophase carbon. It is understood that selecting the above-mentioned materials as the carbon matrix can all serve as a supporting framework and also possesses good electrical conductivity, ensuring the conductivity of the negative electrode material.

[0032] In some embodiments, the carbon matrix comprises porous carbon.

[0033] In some embodiments, porous carbon includes at least one of activated carbon, activated carbon fiber, carbon black, capacitive carbon, mesoporous carbon, carbon nanotubes, and carbon molecular sieves.

[0034] In this application, under stirring, 150 mL of 20% HF acid solution is added dropwise to 10 g of negative electrode material. This generates SiF4 and H2 gases and releases heat. After no more gas is generated, the supernatant acid solution is removed by centrifugation. Another 150 mL of 20% HF acid solution is added to the negative electrode material, and the mixture is stirred for 12 h. The supernatant acid solution is removed by centrifugation again. The negative electrode material is then washed with pure water until neutral and dried to obtain the negative electrode material after removing the silicon material, i.e., the carbon matrix.

[0035] In some embodiments, the negative electrode material after removing the silicon material has pores.

[0036] In some embodiments, the average pore size of the anode material after removing the silicon material is 1.0 nm to 5.2 nm. Specifically, it can be 1.0 nm, 1.64 nm, 1.77 nm, 1.78 nm, 1.79 nm, 1.8 nm, 1.81 nm, 1.98 nm, 2.0 nm, 2.01 nm, 2.5 nm, 3.0 nm, 3.5 nm, 3.8 nm, 4.0 nm, 4.5 nm, 5.0 nm, or 5.2 nm, etc., and is not limited here. The anode material after removing silicon is the carbon matrix. If the pore size of the carbon matrix is ​​too small, the gaseous precursor of silicon material cannot easily penetrate into the pores and tends to accumulate on the carbon matrix surface to form a shell structure, resulting in a decrease in the silicon content inside the anode material and a decrease in the specific capacity of the anode material. If the pore size of the carbon matrix is ​​too large, although it is conducive to silicon material filling, it may cause uneven distribution of silicon material, silicon segregation, and other problems, leading to uneven expansion of the anode material, excessive local expansion stress, particle breakage, and ultimately a decrease in the electrochemical performance of the anode material. Therefore, controlling the average pore size of the carbon matrix within the above-mentioned range is beneficial to the composite of carbon matrix and silicon material, which not only improves the rate performance of the anode material, but also helps to buffer the volume expansion of silicon material and improve the structural stability of the anode material.

[0037] In some embodiments, the specific surface area of ​​the negative electrode material after removing the silicon material is 800 m². 2 / g~2500m 2 / g. Specifically, it could be 800m. 2 / g, 1000m 2 / g、1200m 2 / g, 1500m 2 / g、1560m 2 / g、1649m 2 / g、1657m 2 / g、1669m 2 / g、1676m 2 / g、1680m 2 / g、1681m 2 / g、1686m 2 / g、1689m 2 / g、1694m 2 / g、1701m 2 / g、1800m 2 / g、1805m 2 / g、2000m 2 / g、2100m 2 / g、2200m 2 / g or 2500m 2 / g, etc., can also be other values ​​within the above range, and are not limited here.

[0038] In some embodiments, the total pore volume of the negative electrode material after removing the silicon material is 0.4 cm. 3 / g~1.5cm 3 / g. Specifically, it can be 0.4cm. 3 / g, 0.5cm 3 / g, 0.6cm 3 / g, 0.9cm 3 / g, 1.0cm 3 / g, 1.2cm 3 / g, 1.3cm 3 / g, 1.4cm 3 / g or 1.5cm 3 / g, etc., can also be other values ​​within the above range, and are not limited here. This application controls the total pore volume of the anode material (i.e., carbon matrix) to be within the above range. The carbon matrix can provide sufficient space to accommodate the silicon material, which can not only improve the specific capacity of the anode material, but also ensure that the anode material can reserve an appropriate amount of pores to alleviate the volume expansion caused by the silicon material during lithium insertion / extraction, which is beneficial to improving the cycle performance of the anode material.

[0039] In some embodiments, the silicon material includes at least one of elemental silicon, silicon oxide, and silicon alloy.

[0040] In some embodiments, the elemental silicon includes amorphous silicon and / or crystalline silicon; preferably, the elemental silicon includes amorphous silicon, which expands isotropically during lithium intercalation, thereby reducing the collapse of the pore structure, suppressing rapid capacity decay, and improving the lithium intercalation cycle performance of the anode material.

[0041] In some embodiments, the silicon alloy may be at least one of silicon-lithium alloy, silicon-magnesium alloy, etc., and is not limited thereto.

[0042] In some embodiments, the general formula for silicon oxide is SiO. x Where 0 ≤ x ≤ 2. Specifically, SiO xSpecifically, it could be SiO 0.5 SiO 0.7 SiO 0.9 SiO, SiO 1.2 SiO 1.5 SiO 1.8 SiO 1.9 SiO2, etc., are not limited here.

[0043] In some embodiments, the silicon material includes silicon particles and a silicon oxide layer on the surface of the silicon particles. The silicon oxide layer includes silicon oxide, the general formula of which is SiO. x Where 0 < x ≤ 2. Specifically, SiOx can be SiO 0.5 SiO 0.7 SiO 0.9 SiO, SiO 1.2 SiO 1.5 SiO 1.8 SiO 1.9 SiO2, etc., are not limited here.

[0044] In some embodiments, the silicon material includes silicon particles and a silicon oxide layer on the surface of the silicon particles. The mass percentage of oxygen atoms in the silicon material, based on 100% of the silicon material's mass, is 1% to 18%. Specifically, the mass percentage of oxygen atoms in the silicon material can be 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, or 18%, etc., and is not limited thereto. Controlling the mass percentage of oxygen atoms in the silicon material within the above range is beneficial for forming a stable silicon oxide layer on the surface of the silicon particles, reducing direct contact between the silicon particles and the electrolyte, thereby reducing side reactions between the silicon particles and the electrolyte, and improving the cycle stability of the negative electrode material; it also ensures stable activity of the silicon material, increasing the specific capacity of the negative electrode material.

[0045] In some embodiments, the average particle size of the silicon material is 1 nm to 100 nm. Optionally, the average particle size of the silicon material can specifically be 1 nm, 2 nm, 5 nm, 10 nm, 20 nm, 25 nm, 30 nm, 35 nm, 40 nm, 45 nm, 55 nm, 65 nm, 75 nm, 85 nm, and 100 nm, or other values ​​within this range, which can be selected according to actual needs and are not limited here. The mechanical stress of the silicon material during expansion decreases as the particle size decreases, and the smaller size can shorten the electron and ion transport path. At the same time, the smaller size of the silicon material increases the gap between adjacent silicon materials, which can reserve space for expansion. It is understood that when the average particle size of the silicon material is within the above range, the battery capacity of the lithium-ion battery can be guaranteed and irreversible capacity loss can be reduced. Preferably, the average particle size of the silicon material is 1 nm to 50 nm; more preferably, the average particle size of the silicon material is 1 nm to 10 nm.

[0046] In some embodiments, the morphology of the silicon material includes at least one of dot-like, spherical, ellipsoidal, and sheet-like shapes. The morphology of the silicon material can be selected according to actual needs and is not limited herein.

[0047] In some embodiments, the active particles further include at least one selected from Li, Na, K, Sn, Ge, Fe, Mg, Ti, Zn, Al, P, and Cu. The active particles can be elemental metals.

[0048] In some embodiments, the active particles may specifically include at least one of Sn particles, Ge particles, and Al particles. In other embodiments, the active particles may also be silicon-lithium alloys, silicon-magnesium alloys, etc. Of course, it should be noted that in some cases, the active particles include elemental particles and alloys.

[0049] In some embodiments, the negative electrode material further includes a coating layer located on at least a portion of the surface of the carbon matrix and / or the active particles. The coating layer can reduce the occurrence of solid-liquid interface side reactions between the negative electrode material and the electrolyte. Understandably, the outermost coating layer of the negative electrode material has good electrical conductivity, improving the conductivity of the negative electrode material. Furthermore, it can coat the silicon material exposed on the carbon matrix surface, reducing the continuous oxidation of the exposed silicon material during storage and minimizing the decrease in specific capacity and initial coulombic efficiency (ICE) of the negative electrode material. The coating layer can also reduce direct contact between the silicon material and the electrolyte, ensuring the stability of the SEI film, thereby improving the initial coulombic efficiency of the negative electrode material.

[0050] In some embodiments, the thickness of the coating layer is 0.1 nm to 3000 nm, specifically 0.1 nm, 1 nm, 5 nm, 10 nm, 20 nm, 33 nm, 34 nm, 36 nm, 39 nm, 40 nm, 42 nm, 43 nm, 44 nm, 47 nm, 48 nm, 49 nm, 50 nm, 80 nm, 100 nm, 200 nm, 300 nm, 500 nm, 800 nm, 1000 nm, 2000 nm, or 3000 nm, etc., and of course, other values ​​within the above range are also possible, and are not limited here. Controlling the thickness of the coating layer within the above range can reduce the exposed silicon material on the surface of the negative electrode material, reduce the generation of a large amount of SEI during charging and discharging caused by exposed silicon material, and improve the specific capacity and electrochemical performance of the negative electrode material. Preferably, the thickness of the coating layer is 0.5 nm to 1000 nm, more preferably, the thickness of the coating layer is 5 nm to 500 nm.

[0051] In some embodiments, the coating material includes at least one of carbon, metal oxides, metal fluorides, metal oxyfluorides, and polymers.

[0052] In some embodiments, the coating layer may include lithium-ion permeable carbon, which may include at least one of graphene, soft carbon, and hard carbon. The presence of the coating layer can effectively suppress the volume expansion of the negative electrode material, reduce structural damage to the negative electrode material during cycling, and also enhance the mechanical strength and compressive strength of the negative electrode material.

[0053] In some embodiments, the coating layer may include a lithium-ion-permeable metal oxide, which may include at least one of titanium oxide, aluminum oxide, lithium oxide, cobalt oxide, and vanadium oxide.

[0054] In some embodiments, the coating layer may include aluminum oxide. In certain cases, oxides of other metals that naturally form a protective oxide layer on the surface may be used instead of aluminum oxide. These include, but are not limited to, titanium oxide (Ti), chromium oxide (Cr), tantalum oxide (Ta), niobium oxide (Nb), etc. A variety of oxide coating deposition techniques can be used to deposit such oxide coatings, including physical vapor deposition, chemical vapor deposition, magnetron sputtering, atomic layer deposition, microwave-assisted deposition, wet chemical deposition, etc.

[0055] For example, a metal oxide precursor in the form of a water-soluble salt can be added to a suspension of core particles (in water). The addition of an alkali (e.g., sodium hydroxide or amine) leads to the formation of a metal (M) hydroxide. The core particles suspended in the mixture then serve as nucleation sites for M-hydroxide precipitation. Once the core particles are coated with an M-hydroxide shell, they can be annealed to transform the hydroxide shell into a corresponding oxide layer, which then adheres well to the surface of the anode material.

[0056] In some embodiments, the coating layer comprises a lithium-ion permeable metal fluoride or metal oxyfluoride. Examples of such metal fluoride materials include, but are not limited to: vanadium fluoride, vanadium oxyfluoride, iron fluoride, iron oxyfluoride, aluminum fluoride, aluminum oxyfluoride, titanium fluoride, titanium oxyfluoride, aluminum fluoride, aluminum oxyfluoride, zinc fluoride, zinc oxyfluoride, niobium fluoride, niobium oxyfluoride, tantalum fluoride, tantalum oxyfluoride, nickel fluoride, nickel oxyfluoride, magnesium fluoride, magnesium oxyfluoride, copper fluoride, copper oxyfluoride, manganese fluoride, and manganese oxyfluoride.

[0057] In some implementations, the coating layer comprises a polymer that is permeable to lithium ions.

[0058] In some embodiments, the polymer layer is a conductive polymer. In other embodiments, the polymer is an electrically insulating polymer. Examples of lithium-ion permeable polymers include, but are not limited to, sulfonated polystyrene-grafted fluorinated ethylene propylene, sulfonated inorganic-organic hybrid polymers, partially fluorinated polystyrene, organically modified layered phosphonates, polyphenylene sulfide, polyethers, polysaccharides, polyethylene glycol, and polyethylene oxide.

[0059] In some implementations, the coating may have several (two or more) layers of different lithium-ion permeable materials, including but not limited to lithium-ion permeable metal oxides, lithium-ion permeable metal fluorides, lithium-ion permeable carbon, and lithium-ion permeable polymers.

[0060] In some embodiments, the carbon content in the negative electrode material is 30wt% to 60wt%, specifically 30wt%, 40wt%, 50wt%, 55wt%, or 60wt%, etc., and other values ​​within the above range are also possible and are not limited here. The carbon in the negative electrode material originates from the carbon matrix and coating layer. The composite of carbon and silicon materials can provide a conductive platform and buffer space for the silicon material, improving the structural instability and poor conductivity of the silicon material during cycling. When the mass percentage of carbon in the negative electrode material is within this range, it can provide sufficient distribution sites for the silicon material, which is conducive to the formation of an effective conductive network in the negative electrode material, improving the conductivity and cycle stability of the negative electrode material.

[0061] In some embodiments, the silicon content in the negative electrode material is 30wt% to 65wt%, specifically 30wt%, 35wt%, 40wt%, 45wt%, 46.9wt%, 47.5wt%, 47.7wt%, 47.9wt%, 48.1wt%, 48.2wt%, 48.4wt%, 48.5wt%, 48.6wt%, 48.8wt%, 49.3wt%, 49.9wt%, 50wt%, 50.7wt%, 55wt%, 60wt%, or 65wt%, etc., and other values ​​within the above range are also possible and are not limited here. Preferably, the silicon content in the negative electrode material is 35wt% to 55wt%. When the silicon content in the negative electrode material is within this range, the resulting secondary battery can store a higher amount of electricity, i.e., a higher initial discharge specific capacity.

[0062] In some embodiments, the mass percentage of oxygen in the negative electrode material is ≤5 wt%. Specifically, the mass percentage of oxygen in the negative electrode material can be 0 wt%, 0.8 wt%, 0.9 wt%, 1 wt%, 1.1 wt%, 1.2 wt%, 1.3 wt%, 1.4 wt%, 1.5 wt%, 1.6 wt%, 1.8 wt%, 2 wt%, 2.5 wt%, 3 wt%, 3.5 wt%, 4 wt%, 4.5 wt%, or 5 wt%, and is not limited here. It is understood that if the mass content of oxygen is too high, the silicon material in the negative electrode material will be partially oxidized. Controlling the mass content of oxygen in the negative electrode material within the above range is beneficial for improving the specific capacity of the negative electrode material and reducing the formation of low-activity silicon oxides.

[0063] In some implementations, the specific surface area of ​​the negative electrode material is 1m². 2 / g~10m 2 / g. Specifically, the specific surface area of ​​the negative electrode material can be 1m². 2 / g, 1.4m 2 / g, 1.5m 2 / g, 1.6m 2 / g, 1.7m 2 / g, 1.8m 2 / g, 1.9m 2 / g、2m 2 / g、2.1m 2 / g, 2.2m 2 / g, 2.3m 2 / g, 2.4m 2 / g, 2.5m 2 / g、4m 2 / g、5m 2 / g、7m 2 / g、8m2 / g、9m 2 / g or 10m 2 / g, etc., can also be other values ​​within the above range, and are not limited here. Understandably, the specific surface area of ​​the negative electrode material affects the contact area between the negative electrode material and the electrolyte. When the specific surface area of ​​the negative electrode material is within the above range, the side reactions between the negative electrode material and the electrolyte are reduced, the consumption of active lithium ions is reduced, and the initial coulombic efficiency of the negative electrode material is improved.

[0064] In some embodiments, the tap density of the negative electrode material is 0.7 g / cm³. 3 ~1.1g / cm 3 It can be 0.7g / cm³. 3 0.71g / cm 3 0.75g / cm 3 0.78g / cm 3 0.8g / cm 3 0.85g / cm 3 0.86 g / cm 3 0.88g / cm 3 0.89g / cm 3 0.9g / cm 3 0.91g / cm 3 0.95g / cm 3 0.97g / cm 3 0.98g / cm 3 1.0g / cm 3 1.02g / cm 3 1.05g / cm 3 1.08g / cm 3 Or 1.1g / cm 3 "etc." can also be other values ​​within the above range, and no restrictions are imposed here.

[0065] In some embodiments, the median particle size D50 of the negative electrode material's volume distribution is 0.1 μm to 30 μm, specifically 0.1 μm, 1 μm, 5 μm, 7 μm, 10 μm, 12 μm, 15 μm, 18 μm, 19 μm, 20 μm, or 30 μm, etc., and of course, other values ​​within the above range are also possible, without limitation. In this application, controlling the average particle size of the negative electrode material within the above range is beneficial for improving the cycle performance of lithium-ion batteries made from this negative electrode material.

[0066] In some embodiments, the total pore volume of the negative electrode material is ≤0.1 cm³. 3 / g, specifically 0.1cm 3 / g, 0.08cm 3 / g, 0.07cm 3 / g, 0.06cm 3 / g, 0.05cm 3 / g, 0.04cm 3 / g, 0.03cm 3 / g, 0.024cm 3 / g, 0.02cm 3 / g, 0.015cm 3 / g, 0.012cm 3 / g, 0.011m 3 / g, 0.01cm 3 / g, 0.009cm 3 / g, 0.006cm 3 / g, 0.005cm 3 / g or 0.002cm 3 / g, etc., can also be other values ​​within the above range, and are not limited here. An appropriate amount of porosity in the negative electrode material can reserve space for the volume expansion of the silicon material, alleviate the expansion effect of the negative electrode material, improve the cycle stability of the negative electrode material, and can also adsorb or contain a small amount of gas generated by the side reaction between the silicon material and the electrolyte, thus improving the gas generation phenomenon of the negative electrode material.

[0067] In some embodiments, the pores in the negative electrode material include mesopores.

[0068] In some embodiments, the mesopores in the negative electrode material account for 25% to 95% of the total pore volume. Specifically, this can be 25%, 30%, 35%, 40%, 43%, 44%, 45%, 46%, 49%, 50%, 55%, 57%, 58%, 60%, 66%, 67%, 70%, 75%, 80%, 85%, 90%, 92%, or 95%, etc., and is not limited thereto. Preferably, the mesopores account for 80% to 95% of the total pore volume of the negative electrode material.

[0069] It should be noted that the pores in the negative electrode material are mainly mesopores. When the battery made from the negative electrode material is charged and discharged, the mesopores in the negative electrode material can provide a buffer space for the expansion of the silicon material. On the other hand, it ensures the stress dispersion distribution in the negative electrode material. When the negative electrode material is used in lithium-ion batteries, it can improve the specific capacity of the negative electrode material, alleviate the volume expansion of the silicon material, improve the particle strength of the negative electrode material, and reduce the collapse and breakage of the material structure during electrode rolling or cycling. Thus, under the synergistic effect of the above overall structure, the cycle performance and electrochemical performance of the negative electrode material are improved.

[0070] In some embodiments, the mass ratio of silicon to carbon in the anode material is 0.8 to 2.0, specifically 0.8, 0.9, 0.92, 0.95, 0.98, 1.0, 1.01, 1.02, 1.05, 1.1, 1.2, 1.5, 1.6, 1.8, 1.9, or 2.0, etc., without limitation. When the mass ratio of silicon to carbon in the anode material is <0.8, the specific capacity of the anode material decreases, but the overall cycle performance improves. When the mass ratio of silicon to carbon in the anode material is ≥2.0, the specific capacity of the anode material increases with the increase of silicon content, but the volume expansion effect of silicon is significant, affecting the cycle performance of the anode material. Controlling the mass ratio of silicon to carbon in the anode material within the above range is beneficial for improving the overall specific capacity and cycle stability of the anode material.

[0071] This application provides a method for preparing a negative electrode material, as shown in Figure 1, which is a flowchart of the preparation process of the negative electrode material of this application, including the following steps:

[0072] Step S100: Pre-treat the porous carbonaceous raw material to obtain a carbon matrix, and control the volumetric particle size distribution width α of the carbon matrix to be (D 90 -D 10 ) / (D 50 +D 10 The pore size of the carbon matrix is ​​0.1 ≤ α ≤ 1.4, with an average pore diameter of 1.0 nm to 5.2 nm and a total pore volume of 0.4 cm³. 3 / g~1.5cm 3 / g.

[0073] Step S200: The carbon substrate is preheated to 200℃~400℃, then silicon source gas is introduced, and then the temperature is increased to the deposition temperature at a heating rate of 0.1℃ / min~5℃ / min to obtain the negative electrode material.

[0074] In the above scheme, this application prepares or screens a suitable carbon matrix to control the volumetric particle size distribution width of the carbon matrix within the aforementioned range, resulting in relatively uniform particle size, which is beneficial for the uniform deposition of silicon source gas on the carbon matrix. At the same time, the preheating temperature of the carbon matrix is ​​controlled to maintain the temperature of the carbon matrix between 200 and 400°C, which is beneficial for the silicon source gas to diffuse from the surface of the carbon matrix inward after contacting it. After reaching the interior of the carbon matrix, the silicon source gas decomposes and deposits to form silicon material. By preheating the carbon matrix and the silicon source gas, the deposition uniformity of the silicon material is improved, so that most of the pores of the carbon matrix can be filled by silicon material, thereby increasing the specific capacity of the negative electrode material. Furthermore, after preheating, a very small amount of silane will directly decompose and deposit on the surface of the carbon matrix, which can reduce the occurrence of side reactions between the negative electrode material and the electrolyte. This allows the negative electrode material to have high capacity, first coulombic efficiency, cycle performance, and excellent processing performance.

[0075] The preparation method of this application is described in detail below with reference to the following embodiments:

[0076] Step S100: Pre-treat the porous carbonaceous raw material to obtain a carbon matrix, and control the volumetric particle size distribution width α of the carbon matrix to be (D 90 -D 10 ) / (D 50 +D 10 The pore size of the carbon matrix is ​​0.1 ≤ α ≤ 1.4, with an average pore diameter of 1.0 nm to 5.2 nm and a total pore volume of 0.4 cm³. 3 / g~1.5cm 3 / g.

[0077] In some embodiments, the volumetric particle size distribution width α of the carbon matrix is ​​(D 90 -D 10 ) / (D 50 +D 10 The α value is 0.1 ≤ α ≤ 1.4, specifically 0.1, 0.2, 0.5, 0.6, 0.8, 1.0, 1.1, 1.2, 1.3, or 1.4, or other values ​​within the above range. When α is greater than 1.4, the particle size distribution of the carbon matrix is ​​too wide, resulting in poor particle size uniformity. During subsequent silicon deposition, this can easily lead to an excess of silicon in some carbon matrices and an underabundance of silicon in others, reducing the uniformity of silicon distribution, exacerbating side reactions between the negative electrode material and the electrolyte, and decreasing the initial efficiency of the negative electrode material.

[0078] In some embodiments, the average pore size of the carbon matrix is ​​1.0 nm to 5.2 nm. Specifically, it can be 1.0 nm, 1.8 nm, 2.0 nm, 2.5 nm, 3.0 nm, 3.5 nm, 3.8 nm, 4.0 nm, 4.5 nm, 5.0 nm, or 5.2 nm, etc., and is not limited thereto. If the pore size of the carbon matrix is ​​too small, the gaseous precursor of silicon material is difficult to penetrate into the pores and easily accumulates on the carbon matrix surface to form a shell structure, leading to a decrease in the silicon content inside the negative electrode material and a decrease in the specific capacity of the negative electrode material. If the pore size of the carbon matrix is ​​too large, although it is beneficial for silicon material filling, it may cause uneven distribution of silicon material, silicon segregation, etc., resulting in uneven expansion of the negative electrode material, excessive local expansion stress, particle breakage, etc., and ultimately a decrease in the electrochemical performance of the negative electrode material. Therefore, controlling the average pore size of the carbon matrix within the above range is beneficial to the uniform composite of the carbon matrix and silicon material. This not only improves the rate performance of the anode material, but also helps to buffer the volume expansion of the silicon material and improve the structural stability of the anode material.

[0079] In some embodiments, the specific surface area of ​​the carbon matrix is ​​800 m².2 / g~2500m 2 / g. Specifically, it could be 800m. 2 / g, 1000m 2 / g、1200m 2 / g, 1500m 2 / g、1800m 2 / g、2000m 2 / g、2200m 2 / g or 2500m 2 / g, etc., can also be other values ​​within the above range, and are not limited here.

[0080] In some embodiments, the total pore volume of the carbon matrix is ​​0.4 cm³. 3 / g~1.5cm 3 / g. Specifically, it can be 0.4cm. 3 / g, 0.5cm 3 / g, 0.6cm 3 / g, 0.9cm 3 / g, 1.0cm 3 / g, 1.2cm 3 / g, 1.3cm 3 / g, 1.4cm 3 / g or 1.5cm 3 / g, etc., can also be other values ​​within the above range, and are not limited here. This application controls the total pore volume of the carbon matrix within the above range. The carbon matrix can provide sufficient space to accommodate silicon material, which can not only improve the specific capacity of the anode material, but also ensure that the anode material can reserve an appropriate amount of pores to alleviate the volume expansion caused by the lithium insertion and extraction process of silicon material, which is beneficial to improving the cycle performance of the anode material.

[0081] In some embodiments, the carbon matrix can be prepared by: carbonizing a carbon source, and then mixing the carbonized material with an activator for activation.

[0082] In some embodiments, the carbon source includes at least one of lignin, coconut shell, fruit shell, peanut shell, rice husk, coal-derived biomass, and resin. Coal-derived biomass refers to biomass briquettes, such as the low-pressure compressed product of sawdust, agricultural waste, and paper. The resin may be, for example, polyethylene (PE), polypropylene (PP), polyvinyl chloride (PVC), and polystyrene (PS).

[0083] In some embodiments, the carbonization temperature is 800℃ to 1000℃, specifically 800℃, 850℃, 900℃, 950℃ or 1000℃, etc., and of course other values ​​within the above range are also possible. This application does not limit these values.

[0084] In some embodiments, the activator can be a gaseous activator that reacts with carbon at high temperature using gaseous water vapor, oxygen and nitrogen to generate hydrogen and carbon monoxide. This reaction is used to etch the carbonized material to obtain a carbon matrix with activated pores.

[0085] In some embodiments, the concentration of the gaseous activator is 3% to 20%, specifically 3%, 5%, 7%, 9%, 10%, 12%, 15%, 18%, and 20%, etc., and of course, other values ​​within the above range are also possible, which are not limited herein. Within the above-defined range, a larger amount of activator added results in stronger activation ability, which can form more and more uniformly distributed activation pores in the carbonization material, which is beneficial for subsequent silicon material to fill the activation pores.

[0086] It is understandable that when the activator is water vapor, the concentration of water vapor can be considered as the humidity of water vapor.

[0087] In some embodiments, the activation treatment further includes: acid washing the activated product, wherein the acid used for acid washing is at least one of hydrochloric acid, sulfuric acid, nitric acid, hydrofluoric acid, phosphoric acid, perchloric acid, acetic acid, and benzoic acid.

[0088] In some embodiments, the concentration of the pickling solution is 1 mol / L to 10 mol / L, for example, it can be 1 mol / L, 3 mol / L, 5 mol / L, 8 mol / L, or 10 mol / L, etc., and of course, other values ​​within the above range are also possible, which are not limited here. It is understood that the purpose of pickling is to remove impurities from the material. The material obtained from the carbonization treatment is pickled and then washed with deionized water to wash the product until it is close to neutral.

[0089] In some embodiments, the pickling time is 3h to 8h, for example, it can be 3h, 4h, 5h, 6h, 7h or 8h, etc., and of course it can be other values ​​within the above range, which are not limited here.

[0090] It is understandable that porous carbonaceous raw materials can also be used by purchasing finished porous carbon products directly through commercial channels.

[0091] Step S200: The carbon substrate is preheated to 200℃~400℃, silicon source gas is introduced, and then the temperature is increased to the deposition temperature at a heating rate of 0.1℃ / min~5℃ / min to obtain the negative electrode material.

[0092] In some embodiments, the silicon source gas includes at least one of silane, hexane, and propane.

[0093] In some embodiments, the preheating temperature of the carbon substrate is 200℃ to 400℃, specifically 200℃, 250℃, 300℃, 350℃, and 400℃, or other values ​​within the above range. This application does not impose any limitations on these values. It is understood that silicon source gas is a very reactive gas, decomposing and depositing at temperatures above 400℃, with a very fast reaction rate. During the contact between the silicon source gas and the carbon substrate, surface diffusion typically occurs first, followed by diffusion into the interior of the carbon substrate, and then decomposition and deposition. When the preheating temperature is too high, the silicon source gas begins to decompose directly upon contact with the carbon substrate, causing some silicon material to deposit on the surface of the carbon substrate. When the pores on the carbon substrate surface are blocked, the silicon source gas has difficulty diffusing into the interior of the carbon substrate, resulting in a significant increase in the amount of deposition on the carbon substrate surface, exacerbating the side reactions of the anode material, and significantly reducing the initial efficiency. Controlling the preheating temperature of the carbon matrix within the aforementioned range ensures that silane gas can diffuse from the carbon matrix surface into the interior of the carbon matrix before decomposition and deposition, which is beneficial for improving the deposition uniformity of silicon material. Simultaneously, maintaining the volumetric particle size distribution width of the carbon matrix within the aforementioned range further enhances the uniformity of silicon material distribution within the carbon matrix.

[0094] In some embodiments, the preheating time of the carbon matrix is ​​2h to 6h, specifically 2h, 2.5h, 3h, 3.5h, 4h, 4.5h, 5h, 5.5h and 6h, etc., and of course other values ​​within the above range are also possible, which are not limited here.

[0095] Understandably, by preheating sufficiently, the temperatures of the carbon matrix and the silicon source gas can be made similar, which can reduce the impact of temperature on the uniformity of silicon material deposition when the silicon source gas comes into contact with the carbon matrix.

[0096] In some embodiments, the concentration of the silicon source gas introduced is 5% to 30%, specifically 5%, 8%, 10%, 12%, 15%, 18%, 20%, 23%, 26%, 28%, or 30%, etc. Of course, it can also be other values ​​within the above range, which are not limited here.

[0097] In some embodiments, the temperature of vapor deposition is 500°C to 700°C, specifically 500°C, 550°C, 600°C, 650°C and 700°C, etc., and of course other values ​​within the above range are also possible, which are not limited here.

[0098] In some embodiments, the holding time for vapor deposition is 2h to 25h, specifically 2h, 5h, 10h, 15h, 20h and 25h, etc., and of course other values ​​within the above range are also possible, which are not limited here.

[0099] This application controls the temperature, time, and concentration of the vapor phase active material precursor during vapor deposition, thereby controlling the mass ratio of silicon to carbon in the deposited product, enabling the anode material to possess both high capacity and first-time coulombic efficiency.

[0100] Step S300: Carbon coating treatment is performed on the deposited product using a carbon source to obtain the negative electrode material.

[0101] In some embodiments, the carbon source includes at least one of a gaseous carbon source and a solid carbon source.

[0102] In some embodiments, the gaseous carbon source includes at least one selected from acetylene, methane, propylene, benzene, ethanol, methanol, ethylene, propane, and butane.

[0103] In some embodiments, the flow rate of the gaseous carbon source is 0.1 L / min to 100 L / min, specifically 0.1 L / min, 1 L / min, 10 L / min, 30 L / min, 600 L / min and 100 L / min, etc., and of course other values ​​within the above range are also possible, which are not limited here.

[0104] In some embodiments, the solid carbon source includes at least one selected from sucrose, fructose, glucose, pitch, phenolic resin, polyimide, citric acid, epoxy resin, amino resin, polystyrene, polyacrylic acid, carboxymethyl cellulose, and cellulose acetate butyrate.

[0105] In some embodiments, the mass ratio of the solid carbon source to the precursor is (1 to 100):100, specifically 1:100, 10:100, 30:100, 50:100, 80:100 and 100:100, etc. Of course, it can also be other values ​​within the above range, which are not limited here.

[0106] In some embodiments, the carbon coating treatment temperature is 600℃ to 1100℃, specifically 600℃, 650℃, 700℃, 800℃, 900℃, 1000℃, and 1000℃, etc., and of course, other values ​​within the above range are also possible, which are not limited herein. If the carbon coating treatment temperature is below 600℃, the carbon source will be incompletely carbonized, and a relatively dense carbon layer cannot be obtained; if the carbon coating treatment temperature is above 1100℃, the grain size of the silicon material will increase rapidly, resulting in poor cycle performance and expansion performance of the anode material.

[0107] In some embodiments, the heat preservation time for carbon coating treatment is 2h to 10h, specifically 2h, 5h, 7h, 8h and 10h, etc., and of course other values ​​within the above range are also possible, which are not limited here.

[0108] In some embodiments, the method further includes the steps of sieving and classifying the carbon-coated product.

[0109] In some embodiments, the coating material may also be a metal oxide, for example, after carbon coating, the carbon-coated product may be further coated with a metal-containing coating material.

[0110] In some embodiments, the metal oxide includes at least one of oxides of Sn, Ge, Fe, Cu, Ti, Na, Mg, Al, Ca, and Zn.

[0111] This application also provides a battery. Figure 1 is a schematic diagram of the discharge state of the battery provided in this application embodiment. As shown in Figure 1, the battery includes a casing and an electrode assembly. The electrode assembly includes a positive electrode 1, a negative electrode 2, and a separator 3, with the separator 3 disposed between the positive electrode 1 and the negative electrode 2. The electrode assembly can be a stacked structure, formed by alternately stacking the positive electrode 1, the separator 3, and the negative electrode 2. In other embodiments, the electrode assembly can also be a wound structure, formed by sequentially stacking and winding the positive electrode, the separator, and the negative electrode.

[0112] In some embodiments, the positive electrode 1 includes a positive current collector 101 and a positive active layer 102 disposed on at least one surface of the positive current collector 101.

[0113] In some embodiments, the positive current collector 101 may be made of aluminum foil or nickel foil, or any composite current collector disclosed in the prior art, such as, but not limited to, current collectors formed by combining the aforementioned conductive foil (aluminum foil or nickel foil, etc.) with a polymer substrate. The positive active layer 102 comprises a positive active material, which includes compounds that reversibly insert and deintercalate metal ions.

[0114] In some embodiments, the positive electrode active material may include lithium transition metal composite oxides, sodium transition metal composite oxides, etc. The lithium transition metal composite oxide contains lithium and at least one element selected from cobalt, manganese, and nickel.

[0115] In some embodiments, the positive electrode active material may include, but is not limited to, lithium cobalt oxide (LiCoO2), lithium nickel manganese cobalt ternary materials (NCM), and lithium manganese oxide (LiMn2O3). 4) Lithium nickel manganese oxide (LiNi) 0.5 Mn 1.5 At least one of lithium iron phosphate (LiFePO4) or lithium iron phosphate (LiFePO4).

[0116] In some embodiments, the negative electrode 2 includes a negative electrode current collector 201 and a negative electrode active material layer 202 disposed on at least one surface of the negative electrode current collector.

[0117] In some embodiments, the negative electrode current collector 201 can be at least one of copper foil, nickel foil, stainless steel foil, titanium foil, or carbon-based current collector, or any composite current collector disclosed in the prior art, such as, but not limited to, current collectors formed by combining the aforementioned conductive foil and polymer substrate. The negative electrode active material layer 202 includes a negative electrode material, which is the negative electrode material described in the first aspect or the negative electrode material prepared by the aforementioned preparation method. The battery provided in this application embodiment has the advantages of high capacity, high initial efficiency, long cycle life, excellent rate performance, and low expansion. The battery can be a lithium-ion battery, a sodium-ion battery, a solid electrolyte battery, etc., and is not limited thereto.

[0118] The embodiments of this application will be further described below with reference to several examples. However, the embodiments of this application are not limited to the specific embodiments described below. Appropriate modifications can be made within the scope of the main claims.

[0119] Example 1

[0120] (1) Coconut shells are used as raw materials and carbonized at 950℃. Then, a mixture of water vapor and nitrogen is introduced, with a water vapor concentration of 5.8%, an activation time of 7h, and an activation temperature of 780℃. The activated product is then acid-washed with hydrochloric acid at a concentration of 7mol / L for 3h. After drying, porous carbon is obtained.

[0121] (2) The porous carbon is classified and the particle size of the porous carbon is controlled to obtain porous carbon with a volume particle size distribution width α of 1.31.

[0122] (3) Place the porous carbon in a chemical vapor deposition chamber, introduce silane, control the silane concentration to 15%, first heat to 280℃ and hold for 2h; then heat to 500℃ at a heating rate of 3℃ / min and react for 10h to obtain the precursor.

[0123] (4) Place the precursor in a reactor, introduce methane gas at a concentration of 12%, heat treat at 720°C for 2 hours, and then screen and classify the resulting material to obtain the negative electrode material.

[0124] In this embodiment, the negative electrode material includes a carbon matrix and a silicon material, with at least a portion of the silicon material distributed within the carbon matrix. Other parameters of the negative electrode material are shown in Tables 1 and 2.

[0125] Example 2

[0126] Unlike Example 1:

[0127] In addition to the process parameters specified in Table 1, (4) the precursor is placed in a reactor and propylene gas is introduced at a concentration of 26%. It is then carbon-coated at 650°C for 8 hours. Then it is placed in an atomic layer deposition equipment to deposit TiO2 oxide for 3 hours. The resulting material is then screened and graded to obtain the negative electrode material.

[0128] Example 3

[0129] Unlike Example 1:

[0130] In addition to the process parameters specified in Table 1, (4) the precursor is placed in a reactor and acetylene gas is introduced at a concentration of 14%. The precursor is carbon coated at 520°C and kept at that temperature for 8 hours. Then, titanium source gas and nitrogen source gas are introduced at a temperature of 700°C for 50 minutes. The titanium source gas is the gas formed by the gasification of TiCl2 at 700°C. The carrier gas is argon with a gas velocity of 10 L / min. The nitrogen source gas is nitrogen with a gas velocity of 30 L / min. The obtained material is sieved and graded to obtain titanium oxide coated anode material.

[0131] The following examples (abbreviated as S1 to S14) and comparative examples (abbreviated as D1 to D3) were prepared according to the preparation process of Example 1, and the specific process parameters are shown in Table 1.

[0132] Table 1. Process parameters for the examples and comparative examples.

[0133] Performance testing

[0134] (1) Etching process:

[0135] Under stirring, 150 mL of 20% HF acid solution was added dropwise to 10 g of anode material. This produced SiF4 and H2 gases and released heat. After no more gas was produced, the supernatant acid solution was removed by centrifugation. Another 150 mL of 20% HF acid solution was added to the anode material, and the mixture was stirred for 12 h. The supernatant acid solution was removed by centrifugation again. The anode material was then washed with pure water until neutral and dried to obtain the anode material after removing the silicon material, which is the ideal carbon matrix.

[0136] (2) Test method for the specific surface area of ​​the negative electrode material or the negative electrode material after removing silicon material:

[0137] The specific surface area was measured using a Microtonic TriStar 3000 surface area and pore size analyzer. The static volumetric method according to GB / T19587-2017 "Determination of Specific Surface Area of ​​Solid Substances by Gas Adsorption BET Method" was followed. First, a specific surface area tube (M1) was taken after high-temperature drying and weighed. A certain amount of sample (1 / 2 to 2 / 3 of the tube volume) was then added and degassed at 300℃ for one hour. After cooling, the tube weight (M2) was measured; the sample mass is M2-M1. The sample mass was entered into the computer, and the instrument was used for testing. The instrument automatically completed the test, read the data, and recorded the results. It is important to note that after heating the sample to 300℃ and purging with nitrogen for 1 hour, it was cooled to room temperature, and N2 purging was still required during the cooling process.

[0138] (3) Test method for pore volume of negative electrode material or negative electrode material after removing silicon material:

[0139] The test was conducted using the ASAP2460 instrument from the American company Mack. The pore size distribution data of the material was obtained by DFT simulation analysis using the isothermal adsorption characteristic curve of nitrogen. The average pore size, pore volume, and the proportion of micropore (0-2nm), mesopore (2-50nm), and macropore (>50nm) pore volumes to the total pore volume were then obtained.

[0140] (4) Test method for average particle size of silicon materials:

[0141] The particle size of 20 silicon materials was randomly tested using a high-powered microscope, and then the average particle size of the multiple silicon materials was calculated, which is the average particle size of the silicon material.

[0142] (5) Coating thickness:

[0143] The material was cross-sectioned using a FIB-SEM device. Ten particles were randomly selected from the SEM, and the coating thickness of each particle was measured three times to obtain the average coating thickness.

[0144] (6) Types of silicon materials:

[0145] The type of silicon material is identified by measuring diffraction peaks using an X-ray diffractometer (XRD).

[0146] (7) Test of silicon content in anode material:

[0147] The sample was burned in an oxygen atmosphere using a box-type atmosphere furnace (model: SA2-9-17TP) to allow silicon and silicon suboxide in the sample to react and become silicon dioxide. After carbon combustion, it was converted into carbon dioxide and discharged. The mass content of silicon in the negative electrode material was then calculated by weighing.

[0148] (8) Test of carbon content in negative electrode materials:

[0149] Using a Bruker / Elter G4 ICARUS HF / CS-i infrared carbon-sulfur analyzer, the sample was burned in a high-temperature, oxygen-rich environment. The carbon contained in the sample was oxidized into carbon dioxide, which then entered the infrared detector along with the carrier gas. The carbon content was quantitatively calculated by statistically analyzing the changes in the intensity of the infrared absorption wavelength of the carbon dioxide signal.

[0150] (9) Particle size distribution test of materials:

[0151] The particle size distribution test method refers to GB / T 19077-2016. The particle size distribution range of the negative electrode material was tested using a Malvern laser particle size analyzer (Mastersizer3000). The cumulative particle size distribution based on volume was determined by laser diffraction. D10 represents the particle size corresponding to a cumulative volume distribution percentage of 10%, D50 represents the particle size corresponding to a cumulative volume distribution percentage of 50%, and D90 represents the particle size corresponding to a cumulative volume distribution percentage of 90%.

[0152] (10) Test method for I value of negative electrode material:

[0153] A three-electrode battery was used for charging and discharging. The three-electrode battery consists of a working electrode made of negative electrode material, a reference electrode made of lithium metal, a counter electrode made of lithium metal, and a lithium-ion conductive electrolyte. The three-electrode battery was charged and discharged, and the differential value dQ / dV obtained by differentiating the potential V of the working electrode with reference to the reference electrode with respect to the charge and discharge capacity Q was plotted. The voltage-capacity differential dQ / dV curve showing the relationship between dQ / dV and potential V was also plotted. The maximum value I of the delithiation peak value in the first charge and discharge cycle of the three-electrode battery was measured at a voltage of 1.5V, a current of 0.1C, and a voltage range of 0.005 to 1.5V within the range of 0.4V to 0.5V. A mixture of negative electrode material, conductive carbon black, and polyacrylic acid in a mass ratio of 75:15:10 was dissolved in pure water to obtain a mixture. The solid content of the mixture was controlled at 50%. The mixture was then coated onto a copper foil current collector, vacuum dried, and rolled to obtain a negative electrode sheet, which served as the working electrode in a three-electrode battery. The compaction density of the working electrode was 0.95-1.10 g / cm³. 3 Surface density: 3-4 mg / cm³ 2 A CR2016 analog battery was assembled using a 1 mol / L LiPF6 / ethylene carbonate + dimethyl carbonate + methyl ethyl carbonate (v / v = 1:1:1) electrolyte, a Celgard 2400 separator, and a casing, all manufactured using conventional processes.

[0154] (11) Testing the electrochemical performance of the negative electrode material:

[0155] A mixture of negative electrode material, conductive carbon black, and polyacrylic acid in a mass ratio of 75:15:10 was dissolved in pure water to obtain a compound. The solid content of the compound was controlled at 50%. The compound was coated onto a copper foil current collector, vacuum dried, and rolled to obtain the negative electrode sheet. A lithium metal sheet was used as the counter electrode, and the cells were assembled into a coin cell in an argon-filled glove box. The compaction density of the negative electrode sheet was 0.95-1.10 g / cm³. 3 Surface density: 3-4 mg / cm³ 2 The electrolyte consisted of 1 mol / L LiPF6 / ethylene carbonate + dimethyl carbonate + methyl ethyl carbonate (v / v = 1:1:1), and a Celgard 2400 separator. The coin cell was charged and discharged at a current density of 0.1C within a charge / discharge range of 0.0051V–1.5V. The initial charge specific capacity (q mAh / g), initial discharge specific capacity (mAh / g), and initial coulombic efficiency (ICE) of the coin cell were obtained.

[0156] At room temperature (25℃±2℃), the above-mentioned button cells were subjected to cycle performance tests on the Blue Electric CT2001A battery testing system. The tests were conducted according to the following charge and discharge regime: (1) rest for 6 hours; (2) discharge at 0.1C constant current to 0.01V, discharge at constant voltage to 0.05C; (3) rest for 30 minutes; (4) charge at 0.1C constant current to 1.5V; (5) rest for 30 minutes; (6) discharge at 0.1C constant current to 0.01V, discharge at constant voltage to 0.05C; (7) rest at 25℃ for 180 minutes; (8) charge at 1C constant current to 1.5V; (9) rest for 60 minutes; (10) discharge at 1C constant current to 0.01V, discharge at constant voltage to 0.05C; (11) rest for 30 minutes; (12) repeat steps (8) to (11) 500 times, and then stop the test. The capacity retention rate after 500 cycles is calculated as follows: capacity retention rate after 500 cycles = discharge capacity after 500 cycles / discharge capacity in the first cycle.

[0157] Table 2. Performance parameters of the negative electrode materials in each embodiment and comparative example

[0158] Table 3. Electrochemical performance tests of the negative electrode materials in each example and comparative example.

[0159] Figure 2 shows a scanning electron microscope (SEM) image of the negative electrode material prepared in Example 4, indicating particle dispersion. Figure 3 shows the XRD pattern of the negative electrode material prepared in Example 4, revealing that the silicon material is primarily amorphous silicon. Figure 4 shows the initial charge-discharge curve of the negative electrode material prepared in Example 4, demonstrating a high initial charge-discharge capacity of 1925 mAh / g and an initial coulombic efficiency of 92.7%. Figure 5 shows the cycle performance curve of the negative electrode material prepared in Example 4, and Figure 6 shows the voltage-capacity differential dQ / dV curve. Figures 5 and 6 show excellent cycle performance, with a capacity retention of 93.8% after 500 cycles.

[0160] Based on the test data in Tables 1 to 3, the negative electrode material prepared in this application embodiment is controlled within a suitable range (1 < γ ≤ 2.2) by controlling the ratio γ of the maximum value of the delithiation peak of the negative electrode material to the specific capacity of the first charge. This ensures that most of the silicon material is uniformly distributed in the carbon matrix, thereby improving the specific capacity of the negative electrode material. At the same time, since most of the silicon material is inside the carbon matrix, the side reactions between the negative electrode material and the electrolyte are reduced during the first charge and discharge process. The negative electrode material can have both high specific capacity, high first coulombic efficiency, and excellent cycle stability.

[0161] According to the test data of Comparative Example 1 and Example 1, due to the excessively large volumetric particle size distribution of the carbon matrix, uneven deposition of some silicon material is likely to occur during the silicon vapor deposition process. Some silicon material is deposited on the surface of the carbon matrix, resulting in an increase in the I value, which in turn increases the γ value. Combined with the data in Table 3, it can be seen that the γ value of the negative electrode material is out of the appropriate range, and the specific capacity of the negative electrode material in Comparative Example 1 is reduced. This is because the side reaction between the silicon material exposed on the surface of the negative electrode material and the electrolyte is aggravated, which leads to an aggravated irreversible loss of lithium ions. Therefore, the initial coulombic efficiency of the battery prepared by the negative electrode material decreases, and the cycle retention rate also decreases.

[0162] According to the test data of Comparative Example 2 and Example 1, the carbon substrate was not preheated to 200℃~400℃ before vapor phase silicon deposition. Due to insufficient preheating of the carbon substrate, some silicon material was deposited on the surface of the carbon substrate, resulting in an increase in the I value, which in turn increased the γ value. Combined with the data in Table 3, it can be seen that the specific capacity of the negative electrode material decreased. This is because the side reaction between the silicon material exposed on the surface of the negative electrode material and the electrolyte was intensified, which led to an increase in the irreversible loss of lithium ions. The initial coulombic efficiency of the battery prepared by the negative electrode material decreased, the initial specific capacity also decreased significantly, and the cycle retention rate of the battery also decreased.

[0163] According to the test data of Comparative Example 3 and Example 1, the heating rate of 10℃ / min during the silicon vapor deposition process of the carbon matrix is ​​too fast, resulting in a large temperature difference in the reactor. Since the heating of carbon particles in the reactor requires a transmission time, the carbon matrix particles on the outside are at a higher temperature, while the carbon matrix particles in the central area are at a lower temperature. This temperature difference makes it easy for the silicon material deposition to be uneven. Some silicon material is deposited on the surface of the carbon matrix, which leads to an increase in the I / q ratio, a decrease in the initial coulombic efficiency of the battery, and a decrease in the cycle retention rate.

[0164] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A negative electrode material, characterized in that, It includes a carbon matrix and active particles, wherein the active particles include silicon material, and at least a portion of the silicon material is distributed within the carbon matrix; The negative electrode material satisfies 1 < γ ≤ 2.2, γ = I / q, I μAh / V represents a delithiation peak value in the voltage capacity differential dQ / dV curve of a three-electrode type battery made of the negative electrode material in the range of 0.4 V to 0.5 V, q mAh / g represents the first charge specific capacity of a button type battery made of the negative electrode material at 1.5 V voltage, and the unit of γ is 10 -3 g / V.

2. The negative electrode material according to claim 1, characterized in that, The negative electrode material has at least one of the following characteristics: (1) γ is 2.2, 2.18, 2.14, 2.11, 2.1, 2.09, 2.05, 2.03, 2.0, 1.95, 1.87, 1.8, 1.79, 1.6, 1.5, 1.4, 1.2, 1.15, 1.1 or any value within the range of any two of the above values; (2)1000≤q≤3300； (3)2000≤I≤6600。 3. The negative electrode material according to claim 1, characterized in that, The negative electrode material has at least one of the following characteristics: (1) The carbon matrix includes at least one of hard carbon, soft carbon and mesophase carbon; (2) The carbon matrix includes porous carbon, which includes at least one of activated carbon, activated carbon fiber, carbon black, capacitive carbon, mesoporous carbon, carbon nanotubes and carbon molecular sieves.

4. The negative electrode material according to claim 1, characterized in that, The negative electrode material has at least one of the following characteristics: (1) The silicon material includes at least one of elemental silicon, silicon oxide, and silicon alloy; (2) The silicon material includes elemental silicon, which includes amorphous silicon and / or crystalline silicon; (3) The silicon material includes silicon oxide, and the general formula of the silicon oxide is SiO. x Where 0 < x ≤ 2; (4) The silicon material includes silicon particles and a silicon oxide layer on the surface of the silicon particles. The mass percentage of oxygen in the silicon material is 1%-18% based on the mass of the silicon material being 100%. (5) The active particles also include at least one of Li, Na, K, Sn, Ge, Fe, Mg, Ti, Zn, Al, P and Cu.

5. The negative electrode material according to claim 1, characterized in that, The negative electrode material has at least one of the following characteristics: (1) The specific surface area of ​​the negative electrode material after removing silicon is 800 m². 2 / g~2500m 2 / g; (2) The total pore volume of the negative electrode material after removing the silicon material is 0.4 cm³. 3 / g~1.5cm 3 / g; (3) The average pore size of the negative electrode material after removing silicon material is 1.0 nm to 5.2 nm.

6. The negative electrode material according to claim 1, characterized in that, The negative electrode material has at least one of the following characteristics: (1) The negative electrode material further includes a coating layer, which is located on at least a portion of the surface of the carbon matrix and / or the active particles; (2) The negative electrode material further includes a coating layer, the thickness of which is 0.1 nm to 3000 nm; (3) The negative electrode material further includes a coating layer, the thickness of which is 5nm to 500nm.

7. The negative electrode material according to claim 1, characterized in that, The negative electrode material has at least one of the following characteristics: (1) The average particle size of the silicon material is 1 nm to 100 nm; (2) The average particle size of the silicon material is 1 nm to 10 nm; (3) The morphology of the silicon material includes at least one of the following: dot-shaped, spherical, ellipsoidal and sheet-like.

8. The negative electrode material according to claim 1, characterized in that, The negative electrode material has at least one of the following characteristics: (1) The active particles also include at least one of Sn particles, Ge particles, and Al particles; (2) The active particles also include silicon-lithium alloy or silicon-magnesium alloy.

9. The negative electrode material according to claim 6, characterized in that, The negative electrode material has at least one of the following characteristics: (1) The material of the coating layer includes at least one of carbon, metal oxide, metal fluoride, metal oxyfluoride and polymer; (2) The material of the coating layer includes carbon, and the carbon includes at least one of graphene, soft carbon and hard carbon; (3) The material of the coating layer includes metal oxides, and the metal oxides include at least one of titanium oxide, aluminum oxide, lithium oxide, cobalt oxide and vanadium oxide.

10. The negative electrode material according to any one of claims 1 to 9, characterized in that, The negative electrode material has at least one of the following characteristics: (1) The specific surface area of ​​the negative electrode material is 1m². 2 / g~10m 2 / g; (2) The median particle size D of the volume distribution of the negative electrode material 50 The range is from 0.1 μm to 30 μm; (3) The volumetric particle size distribution width P of the negative electrode material is P = (D 90 -D 10 ) / (D 50 +D 10 ), 0.1≤P≤1.

4.

11. The negative electrode material according to any one of claims 1 to 9, characterized in that, The negative electrode material has at least one of the following characteristics: (1) The total pore volume of the negative electrode material is ≤0.1 cm³. 3 / g; (2) The tap density of the negative electrode material is 0.7 g / cm³. 3 ~1.1g / cm 3 .

12. The negative electrode material according to any one of claims 1 to 9, characterized in that, The negative electrode material has at least one of the following characteristics: (1) The pores in the negative electrode material include mesopores, and the volume ratio of the mesopores in the total pore volume of the negative electrode material is 25% to 95%; (2) The pores in the negative electrode material include mesopores, and the volume ratio of mesopores in the total pore volume of the negative electrode material is 80%-95%.

13. The negative electrode material according to any one of claims 1 to 9, characterized in that, The negative electrode material has at least one of the following characteristics: (1) The mass percentage of oxygen in the negative electrode material is ≤5wt%; (2) The carbon content in the negative electrode material is 30wt% to 60wt%.

14. The negative electrode material according to any one of claims 1 to 9, characterized in that, The negative electrode material has at least one of the following characteristics: (1) The mass percentage of silicon in the negative electrode material is 30wt% to 65wt%; (2) The mass ratio of silicon to carbon in the negative electrode material is 0.8 to 2.

0.

15. A battery, characterized in that, The battery comprises the negative electrode material as described in any one of claims 1 to 14.

Images