Negative electrode material, preparation method thereof and lithium ion battery

Abstract

The present disclosure relates to a negative electrode material, a preparation method thereof, and a lithium ion battery. The negative electrode material includes an active material, the active material includes a framework structure and a silicon-oxygen material embedded in the framework structure, the framework structure includes a lithium silicate framework located inside the active material and a water-insoluble silicate framework located on the surface layer of the active material, the water-insoluble silicate framework and the lithium silicate framework are connected, and in the XRD pattern of the negative electrode material, the intensity of the strongest characteristic diffraction peak of the lithium silicate is I A and the intensity of the strongest characteristic diffraction peak of water-insoluble silicates is I B and I B / I A is 0.03≦I B / I A The negative electrode material and the preparation method thereof according to the present disclosure are simple to prepare, low-cost, and suitable for mass production. The prepared negative electrode material can improve processability, and has excellent electrochemical performance, cycle performance, and expansion inhibition performance, and can extend the service life of lithium-ion batteries.

Description

[Technical Field]

[0001] The present disclosure is in the field of lithium ion batteries and relates to a negative electrode material, a method for preparing the same, and a lithium ion battery.

[0002] Cross-reference to related applications This disclosure claims priority to a Chinese application filed with the China Patent Office on December 29, 2021, bearing application number CN202111635594.X and entitled "Silicon-oxygen composite negative electrode material, preparation method thereof, and lithium-ion battery," the entire contents of which are incorporated herein by reference. [Background technology]

[0003] Silicon suboxide materials are essential anode materials for next-generation ultra-high-capacity lithium-ion batteries. Although the silicon suboxide industry has been developing silicon-based lithium-ion batteries for over a decade, silicon suboxide and other silicon-based materials have yet to be widely applied. The application of silicon-based materials is limited by the shortage of silicon-based materials themselves. Issues such as large expansion, rapid volume change, low first-time coulombic efficiency, and low rate performance need to be addressed as soon as possible. Metal doping of silicon-based cores is one of the most straightforward methods for improving the first-time coulombic efficiency of silicon-based anode materials. Doping with a reducing metal to form an inert silicate prevents the reaction of active lithium with oxygen during lithium intercalation and deintercalation, thereby improving the first-time coulombic efficiency of silicon-oxygen materials. Metals with a certain degree of reducing ability, such as Li or Mg, should be selected for doping. Metallic lithium is one of the most preferred active elements in lithium-ion batteries. After prelithiation, silicon-based materials form inert materials such as various phases of lithium silicates inside. These lithium silicates not only act as buffers for expansion during charging and discharging, but also function as superionic conductors, facilitating the rapid internal migration of lithium ions due to the high lithium content at their interfaces. In both academia and industry, the prelithiation process is one of the most efficient methods for improving the initial coulombic efficiency of silicon-based materials.

[0004] However, pre-lithiated silicon-based materials present many problems that need to be addressed. The most serious of these is gas generation and loss of active silicon due to uncontrollable pH. After pre-lithiated silicon-based materials, while lithium is incorporated into the silicon-based core, strongly alkaline silicates and other residual alkalis are formed on the surface. These components result in a strongly alkaline slurry when prepared. In a strongly alkaline environment, silicon-based materials undergo oxidation-reduction reactions, releasing hydrogen, resulting in the loss of oxidized active silicon and the formation of dead silicon, which reduces battery capacity. Furthermore, the released hydrogen affects the quality of the electrode plates during the slurry application process.

[0005] Therefore, the development of silicon-based materials with reduced gas generation, improved processability, and excellent cycle performance, and a method for preparing the same, has become a technical challenge in the field. Summary of the Invention

[0006] The present disclosure provides a negative electrode material, the negative electrode material comprising an active material, the active material comprising a framework structure present throughout the active material and a silicon-oxygen material embedded in the framework structure, the framework structure comprising a lithium silicate framework located inside the active material and a water-insoluble silicate framework located on the surface layer of the active material, the water-insoluble silicate framework and the lithium silicate framework being connected to each other, and an XRD pattern of the negative electrode material, the intensity of the strongest characteristic diffraction peak of the lithium silicate being I A and the intensity of the most intense characteristic diffraction peak of the water-insoluble silicate is I B and I B / I A is 0.03≦I B / I A ≦0.2.

[0007] The present disclosure further provides a negative electrode material, the negative electrode material comprising an active material, the active material comprising lithium silicate, a water-insoluble silicate, and a silicon-oxygen material, the water-insoluble silicate being formed so as to coat a surface of the lithium silicate, the silicon-oxygen material being contained in at least one of the lithium silicate and the water-insoluble silicate, and an XRD pattern of the negative electrode material, the intensity of the strongest characteristic diffraction peak of the lithium silicate being I A and the intensity of the most intense characteristic diffraction peak of the water-insoluble silicate is I B and I B / I A is 0.03≦I B / I A ≦0.2.

[0008] Optionally, the silicon oxygen material is SiO n where n satisfies 0.5≦n≦1.5.

[0009] Optionally, the lithium silicate comprises at least one of Li2SiO3, Li2Si2O5, Li4SiO4, Li2Si3O7, Li8SiO6, Li6Si2O7, Li4Si2O7, Li2Si4O7 and LiSiO3.

[0010] Optionally, the water insoluble silicate is zAO MO y xSiO2, wherein M contains at least one of Mg, Al, Ca, Ge, Cr, V, Ti, Sc, Co, Ni, Cu, Sr, Zn, Zr, Fe, and Mn, A contains at least one of Li, Na, and K, and x satisfies 0.2≦x≦10.0, y satisfies 1.0≦y≦3.0, and z satisfies 0≦z≦5.0.

[0011] Optionally, the water-insoluble silicate further comprises A2O·nSiO2, where A comprises at least one of Li, Na, and K, and n satisfies 1≦n≦10.

[0012] Optionally, the work function range of the water-insoluble silicate satisfies 2.5 eV≦η≦7.0 eV.

[0013] Optionally, the water-insoluble silicate is located within a region from the surface of the active material to a depth of 20 nm to 50 nm.

[0014] Optionally, the mass content of Li element in the water-insoluble silicate is W1%, and the mass content of Li element in the lithium silicate is W2%, satisfying W2>W1≧0.

[0015] Optionally, the negative electrode material further comprises a carbon layer formed on the surface of the active material.

[0016] Optionally, the carbon layer has an average thickness of 30 nm to 500 nm.

[0017] Optionally, the tap density of the negative electrode material is 0.6 g / cm 3 ~1.20g / cm 3 is.

[0018] Optionally, the specific surface area of ​​the negative electrode material is 1.00 m 2 / g~12.0m 2 / g.

[0019] Optionally, the negative electrode material has an average particle size of 3.0 μm to 12.0 μm.

[0020] Optionally, the mass content of carbon in the negative electrode material is 1.5 wt% to 10.0 wt%.

[0021] Optionally, the mass content of lithium in the negative electrode material is 3 wt% to 15 wt%.

[0022] Optionally, the pH of the negative electrode material is 8.5 to 12.0.

[0023] Optionally, in the XRD pattern of the negative electrode material, the intensity of the strongest characteristic diffraction peak of lithium silicate is I A and the intensity of the strongest characteristic diffraction peak of water-insoluble silicates is I B and I B / IA is 0.12≦I B / I A ≦0.18.

[0024] Optionally, the content of lithium element in the water-insoluble silicate of the negative electrode material is pm, and the total content of lithium element in the negative electrode material is p Li and 0.01≦pm / p Li ≦0.6.

[0025] The present disclosure further provides a method for preparing an anode material, the method comprising the steps of: subjecting a pre-lithiated silicon-oxygen material to a surface etching treatment; and mixing the surface-etched silicon-oxygen material with a substance containing at least one of metal M and metal A, and conducting a solid-state thermal reaction under a protective gas atmosphere to obtain the anode material.

[0026] Optionally, the metal A-containing material includes at least one of metal A alone, a carbonate of metal A, an oxide of metal A, and a hydroxide of metal A, where A includes at least one of Li, Na, and K.

[0027] Optionally, the metal M-containing material comprises at least one of metal M alone, a carbonate of metal M, an oxide of metal M, and a hydroxide of metal M, wherein M comprises at least one of Mg, Al, Ca, Ge, Cr, Pb, Sr, Zn, Zr, Fe, and Mn.

[0028] Optionally, the mass ratio of the surface-etched silicon-oxygen material to the substance containing at least one of metal M and metal A is 1:(0.01 to 0.1).

[0029] Optionally, the mass ratio of the surface-etched silicon-oxygen material to the substance containing at least one of metal M and metal A is 1:(0.075 to 0.1).

[0030] The present disclosure further provides a method for preparing an anode material, the method comprising the steps of: subjecting a pre-lithiated silicon-oxygen material to a surface etching treatment; and mixing the surface-etched silicon-oxygen material with a compound containing metal M, followed by a solid-state thermal reaction under a protective gas atmosphere to obtain an anode material.

[0031] Optionally, the metal M-containing compound comprises at least one of a carbonate of metal M, an oxide of metal M, and a hydroxide of metal M, wherein M comprises at least one of Mg, Al, Ca, Ge, Cr, Pb, Sr, Zn, Zr, Fe, and Mn.

[0032] Optionally, the mass ratio of the surface-etched silicon-oxygen material to the compound containing metal M is 1:(0.01-0.1).

[0033] Optionally, the mass ratio of the surface-etched silicon-oxygen material to the compound containing metal M is 1:(0.075-0.1).

[0034] Optionally, the compound containing metal M is an oxide of metal M.

[0035] Optionally, the mixing method includes at least one of mechanical stirring, ultrasonic dispersion, and abrasive dispersion.

[0036] Optionally, the mixing method is ball milling, and the ball milling time is 3 hours to 24 hours.

[0037] Optionally, the protective gas comprises at least one of nitrogen gas, helium gas, neon gas, argon gas, krypton gas, and xenon gas.

[0038] Optionally, the temperature of the solid-state thermal reaction is 600°C to 1200°C.

[0039] Optionally, the solid-state thermal reaction time is 3 hours to 12 hours.

[0040] Optionally, the temperature rise rate of the solid-state thermal reaction is 1°C / min to 5°C / min.

[0041] Optionally, the prelithiated silicon oxygen material is a prelithiated carbon-coated silicon oxygen material.

[0042] Optionally, the prelithiated carbon-coated silicon and oxygen material is obtained by reacting a carbon-coated silicon and oxygen material with a lithium source.

[0043] Optionally, the silicon oxygen material is SiO n where n satisfies 0.5≦n≦1.5.

[0044] Optionally, the silicon and oxygen material has an average particle size (D50) of 2.0 μm to 15.0 μm.

[0045] Optionally, the carbon layer on the surface of the carbon-coated silicon / oxygen material has a thickness of 30 nm to 500 nm.

[0046] Optionally, the lithium source comprises at least one of lithium or a lithium-containing compound.

[0047] Optionally, the lithium source comprises at least one of lithium hydride, alkyl lithium, metallic lithium, lithium aluminum hydride, lithium amide, and lithium borohydride.

[0048] Optionally, in the reaction between the carbon-coated silicon oxygen material and the lithium source, the reaction temperature is 150°C to 300°C.

[0049] Optionally, the reaction time between the carbon-coated silicon oxygen material and the lithium source is 2.0 hours to 6.0 hours.

[0050] Optionally, the mass ratio of the carbon-coated silicon oxygen material to the lithium source is 1:(0.01-0.20).

[0051] Optionally, the mass content of lithium in the prelithiated carbon-coated silicon-oxygen material is 3 wt% to 20 wt%.

[0052] Optionally, prior to the step of subjecting the pre-lithiated silicon and oxygen material to a surface etching treatment, the method further comprises the step of reacting the silicon and oxygen material with a lithium source to obtain the pre-lithiated silicon and oxygen material, or the step of reacting the carbon-coated silicon and oxygen material with a lithium source to obtain the pre-lithiated carbon-coated silicon and oxygen material.

[0053] Optionally, the acid solution used in the surface etching treatment has properties that maintain a pH of the surface etching reaction system below 7 when the prelithiated silicon oxygen material is subjected to the surface etching treatment.

[0054] Optionally, the acid solution used in the surface etching treatment comprises at least one of hydrochloric acid, acetic acid, nitric acid, citric acid, oxalic acid, sulfuric acid, formic acid, phenol, phosphoric acid, hydrogen phosphate, hydroiodic acid, hydrobromic acid, ethylenediaminetetraacetic acid, glycolic acid, gluconic acid, and succinic acid.

[0055] Optionally, the surface etching treatment time is 0.5 to 10.0 hours.

[0056] The present disclosure further provides a lithium-ion battery comprising the negative electrode material according to the first aspect or prepared by the method for preparing a negative electrode material according to the first aspect. [Brief explanation of the drawings]

[0057] [Figure 1] 1 is a process flow chart of a method for preparing a negative electrode material according to the present disclosure. [Figure 2] FIG. 1 is a schematic diagram of a negative electrode material according to the present disclosure. [Figure 3] FIG. 1 is a schematic diagram of a negative electrode material according to the present disclosure. [Figure 4]FIG. 2 is a schematic diagram showing the change in capacity retention rate of negative electrode materials prepared according to the examples and comparative examples of the present disclosure as the number of cycles increases. [Figure 5] FIG. 2 is a schematic diagram showing the change in conductivity of negative electrode materials prepared according to each of the examples and comparative examples of the present disclosure. [Figure 6] 1 is an XRD diffraction pattern of a negative electrode material prepared according to Example 3 of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0058] In order to better explain the present disclosure and easily understand the technical solutions of the present disclosure, the present disclosure will be described in more detail below. The following examples are merely illustrative examples of the present disclosure and do not represent or limit the protection scope of the present disclosure, which is subject to the scope of the claims.

[0059] The present disclosure provides a negative electrode material, a preparation method thereof, and a lithium-ion battery, which can improve processability, electrochemical performance, cycle performance, and expansion suppression performance, thereby extending the service life of lithium-ion batteries and reducing production costs.

[0060] One embodiment of the present disclosure provides a negative electrode material. The negative electrode material includes an active material, the active material including a framework structure present throughout the active material and a silicon-oxygen material embedded in the framework structure. The framework structure includes a lithium silicate framework located inside the active material and a water-insoluble silicate framework located on the surface layer of the active material, and the water-insoluble silicate framework and the lithium silicate framework are connected. In the XRD pattern of the negative electrode material, the intensity of the strongest characteristic diffraction peak of lithium silicate is I A and the intensity of the strongest characteristic diffraction peak of water-insoluble silicates is I B and I B / I A is 0.03≦I B / I A ≦0.2.

[0061] Optionally, I B / I A The range of is, for example, 0.05≦I B / I A ≦0.2, 0.1≦I B / I A ≦0.2, I B / I A is 0.12≦I B / I A ≦0.18 or 0.14≦I B / I A ≦0.16.

[0062] As used herein, the term "skeleton" refers to a primary substance (e.g., a structure considered as an integral unit, a block structure, a sheet-like structure, a layered structure, a core structure, a shell structure, etc.) that forms a specific structure (e.g., the primary substance accounts for 51% or more of the total weight of the structure), i.e., the primary substance is a basic substance that supports, forms, or constitutes a specific structure. For example, in the case of a "lithium silicate skeleton," lithium silicate can be understood to be the primary component forming the lithium silicate-containing structure and the basic substance that supports, forms, or constitutes the lithium silicate-containing structure, and other components (e.g., silicon-oxygen materials according to the present disclosure) may be dispersed or embedded within the lithium silicate-containing structure. For example, in the case of a "water-insoluble silicate skeleton," water-insoluble silicate can be understood to be the primary component forming the water-insoluble silicate-containing structure and the basic substance that supports, forms, or constitutes the water-insoluble silicate-containing structure, and other components (e.g., silicon-oxygen materials according to the present disclosure) may be dispersed or embedded within the water-insoluble silicate-containing structure.

[0063] In some embodiments, the negative electrode material comprises an active material 100, as shown in FIG.

[0064] The active material 100 includes a lithium silicate 120, a water-insoluble silicate 140, and a silicon-oxygen material 160;

[0065] The water-insoluble silicate 140 is formed so as to cover the surface of the lithium silicate 120,

[0066] At least one of the lithium silicate 120 and the water-insoluble silicate 140 includes the silicon and oxygen material 160;

[0067] In the XRD pattern of the negative electrode material, the intensity of the strongest characteristic diffraction peak of the lithium silicate is I A and the intensity of the most intense characteristic diffraction peak of the water-insoluble silicate is I B and I B / I A is 0.03≦I B / I A ≦0.2.

[0068] In some embodiments, as seen in the preparation method below, the prelithiated silicon-oxygen material is subjected to surface etching (the material is primarily comprised of lithium silicate 120, typically a core of lithium silicate 120 with a silicon dioxide layer formed on the surface), followed by void formation for the formation of a water-insoluble silicate, and then reacted with a substance containing at least one of metal M and metal A to form a structure in which the water-insoluble silicate coats the lithium silicate 120.

[0069] The pre-lithiated silicon-oxygen material then undergoes a subsequent high-temperature treatment to cause a disproportionation reaction of the silicon-oxygen compound, forming a structure in which the silicon-oxygen material 160 is dispersed or embedded in at least one of the lithium silicate 120 and the water-insoluble silicate 140.

[0070] Optionally, the water-insoluble silicate 140 includes, but is not limited to, a silicate that is insoluble in a polar solution (eg, an aqueous solution).

[0071] Optionally, the silicon oxygen material (or referred to as silicon-based active material) comprises at least one of nanosilicon, silicon oxide, silicon carbide, silicon nitride, silicon sulfide, or silicon alloy.

[0072] As shown in FIG. 3, optionally, the negative electrode material further includes a coating layer 200 formed to coat the surface of the active material 100 .

[0073] In the above proposal, silicon-oxygen materials (also known as silicon-based active materials, including nanosilicon, silicon oxide, silicon carbide, silicon nitride, silicon sulfide, and silicon alloys) are embedded in a framework (i.e., silicate framework), and the water-insoluble silicate outer layer and the lithium silicate inner layer are grown on the same silicon-oxygen framework to form different crystalline silicates. The two different silicate materials are connected, which is beneficial to the electrochemical performance of the active material, accelerating electron transfer and lithium intercalation / deintercalation, lowering the material's internal resistance, and improving lithium ion mobility. Coating the silicon-oxygen materials with the water-insoluble silicate framework formed on the outer layer effectively prevents contact between water and the strongly alkaline lithium silicate, inhibiting the hydrolysis of the lithium silicate. This effectively reduces gas generation in the material, allows control over the material's pH, and improves processability. The lithium silicate in the inner layer and the water-insoluble silicate in the outer layer are tightly connected by the silicon and silicon-oxygen materials. Due to the difference in work functions between the two silicate materials, a heterojunction interface is formed between them, resulting in increased electron transfer efficiency at the junction interface, thereby improving lithium insertion depth and capacity and cycle performance. The lithium silicate and the water-insoluble silicate are silicates of different crystal types grown on the same silicon-oxygen framework, forming a tight heterojunction interface without forming a vacuum cross section, which is beneficial for electron transfer between the heterojunction materials. Lithium ions are effectively conducted between the framework structure and the silicon-oxygen material on the active material surface, improving the ionic conductivity of the material and favoring the material's rate performance.

[0074] The following are alternative technical solutions of the present disclosure and do not limit the technical solutions according to the present disclosure. Through the following alternative technical solutions, the technical objectives and beneficial effects of the present disclosure can be better realized.

[0075] As an alternative technical solution of the present disclosure, the silicon oxygen material is SiO n where n satisfies 0.5 ≤ n ≤ 1.5. Optionally, the silicon oxygen material SiO n is, for example, SiO 0.5 、SiO 0.8 、SiO 0.9 、SiO, SiO 1.1 、SiO 1.2 or SiO 1.5 etc. Optionally, the silicon oxygen material is SiO. Note that SiO n has a relatively complex composition and can be understood as being formed by uniformly dispersing nanosilicon in SiO2. Exemplarily, the silicon oxygen material may include at least two of elemental silicon, silicon dioxide, and silicon suboxide.

[0076] As an alternative technical solution of the present disclosure, lithium silicate includes at least one of Li2SiO3, Li2Si2O5, Li4SiO4, Li2Si3O7, Li8SiO6, Li6Si2O7, Li4Si2O7, Li2Si4O7, and LiSiO3. As an alternative technical solution of the present disclosure, lithium silicate includes Li2O·mSiO2, where m satisfies 0 < m ≤ 2, for example, m is 0.1, 0.3, 0.5, 0.7, 0.9, 1.0, 1.2, 1.4, 1.5, 1.6, 1.8, or 2.

[0077] As an alternative technical solution of the present disclosure, the water-insoluble silicate is zA2O·MO yxSiO2, where M contains at least one of Mg, Al, Ca, Ge, Cr, V, Ti, Sc, Co, Ni, Cu, Sr, Zn, Zr, Fe, and Mn, A contains at least one of Li, Na, and K, and x satisfies 0.2≦x≦10.0, y satisfies 1.0≦y≦3.0, and z satisfies 0≦z≦5.0. At least one of metal A and metal M is embedded in the silicon-oxygen framework to form a water-insoluble silicate framework structure.

[0078] In some embodiments, the water-insoluble silicate further comprises A2O·nSiO2, where A comprises at least one of Li, Na, and K, and n satisfies 1≦n≦10.

[0079] As an optional technical solution of the present disclosure, the water-insoluble silicate includes, but is not limited to, Mg2SiO4, Al2SiO5, CaSiO3, LiAlSiO4, LiAlSiO, LiAlSi2O6, LiAlSi3O8, Li2MgSiO4, MgSiO3, or Li2CaSiO4.

[0080] To speed up electron conduction and increase the powder conductivity of the material, the work function of the water-insoluble silicate can be selected within a range of 2.5 eV≦η≦7.0 eV, and optionally 4.50 eV≦η≦6.5 eV. This ensures processability and is favorable for increasing electron transfer efficiency, significantly increasing powder conductivity. Furthermore, an appropriate work function range can improve the efficiency of electron transfer between heterojunctions. Since the water-insoluble silicate skeleton is in direct contact with the conductive carbon layer as the outer layer skeleton, if the work function of the water-insoluble silicate is higher than that of the carbon layer but lower than that of the lithium silicate, it can contribute to the transfer of electrons from the outer layer to the interior, improving conductivity.

[0081] In an optional technical solution of the present disclosure, the water-insoluble silicate is located within a region from the surface of the active material to a depth of 20 nm to 50 nm, for example, 25 nm to 45 nm, 28 nm to 38 nm, or 30 nm to 35 nm, such as 20 nm, 24 nm, 26 nm, 28 nm, 30 nm, 34 nm, 36 nm, 38 nm, 40 nm, 44 nm, 46 nm, 48 nm, 50 nm, or a range defined by any two of the above values. That is, the water-insoluble silicate is located within a region from the surface of the active material to a depth of, for example, 20 nm to 50 nm in the radial direction. Because the water-insoluble silicate is located in the surface layer of the active material, the surface layer structure composed of the water-insoluble silicate skeleton and the silicon-oxygen material distributed in the water-insoluble silicate skeleton can prevent the electrolyte from penetrating into the active material, preventing contact between water and the strongly alkaline lithium silicate, and effectively suppressing hydrolysis of the lithium silicate.

[0082] In one alternative technical solution of the present disclosure, a water-insoluble silicate framework and a lithium silicate framework are connected to form a heterojunction structure. A silicon-oxygen material is embedded in the framework structure, connecting the water-insoluble silicate framework and the lithium silicate framework through the silicon-oxygen material, thereby connecting the two frameworks to form a distinct heterojunction. This heterojunction is composed of lithium silicate and a water-insoluble silicate, and because both the lithium silicate and the water-insoluble silicate react and grow within the same SiO2 framework, the junction between the interfaces is tight and continuous, avoiding the formation of a vacuum cross section and favoring electron transfer between the heterojunction materials. This heterojunction can promote electron transfer within the active material due to the difference in work function between the interfaces and the appropriate interfacial distance, thereby improving electrical conductivity. The heterojunction structure effectively improves the electrical conductivity of the active material, increasing the initial Coulombic efficiency of the material, while also suppressing hydrolysis and controlling pH.

[0083] As an optional technical solution of the present disclosure, in the XRD pattern of the negative electrode material, the intensity of the characteristic diffraction peak of lithium silicate is I Aand the intensity of the characteristic diffraction peak of water-insoluble silicates is I B and I B / I A is 0.03≦I B / I A Meets ≦0.20. B / I A By controlling the value of I, the electron transport ability of the heterojunction can be maximized, and the electron conductivity can reach 15 S / cm or more, which is advantageous for the rate performance of the material. B / I A is 0.12≦I B / I A ≦0.18, thus ensuring processability and ensuring high electrical conductivity of the silicon-based material.

[0084] When the water-insoluble silicate is lithium silicate, the intensity of the characteristic diffraction peak of the water-insoluble silicate is I c The intensity of the characteristic diffraction peak of the lithium silicate inside the active material is I, and the water-insoluble lithium silicate is subjected to acid washing until it no longer reacts, and the intensity of the characteristic diffraction peak of the treated water-insoluble silicate is I D and 0.03≦(I C -I D ) / 2I≦0.2. The purpose of pickling is to remove the insoluble lithium silicate on the surface and leave SiO2 (silicon-oxygen skeleton) to deposit on the surface, and the acid solution is sulfuric acid, hydrochloric acid, nitric acid, aqua regia, etc. When the water-insoluble silicate is water-insoluble lithium silicate, (I C -I D By controlling the value of ) / 2I, the electron transport capacity of the heterojunction can be maximized, the rate performance of the material can be effectively demonstrated, and the high conductivity of the silicon-based material can be ensured.

[0085] In an alternative technical solution of the present disclosure, the mass content of Li in the water-insoluble silicate on the surface of the active material is W1%, and the mass content of Li in the lithium silicate inside the active material is W2%, where W2 > W1 ≥ 0 is satisfied. That is, the concentration of Li on the surface of the active material is lower than the concentration of Li inside the active material. The lithium silicate is mainly located inside the active material, and the water-insoluble silicate is located in the outer layer of the active material. This silicon-oxygen material coated with the water-insoluble silicate framework can prevent the electrolyte from entering the active material and prevent contact between water and the strongly alkaline lithium silicate, effectively inhibiting the hydrolysis of the lithium silicate, achieving pH control, and suppressing gas generation.

[0086] Optionally, the negative electrode material further includes a carbon layer formed on the surface of the active material, which allows the water-insoluble silicate framework and the silicon-oxygen material embedded therein to directly contact with the carbon layer, thereby ensuring the stability of the conductive channel and the lithium ion transport channel within the particle.

[0087] Optionally, the material of the carbon layer is at least one selected from hard carbon, soft carbon, carbon nanotube, nanocarbon fiber, graphite, and graphene.

[0088] The average thickness of the carbon layer is 30 nm to 500 nm. Optionally, the thickness of the carbon layer is, for example, 60 nm to 450 nm, 120 nm to 350 nm, or 220 nm to 320 nm, such as 30 nm, 50 nm, 100 nm, 150 nm, 200 nm, 250 nm, 300 nm, 350 nm, 400 nm, 450 nm, 500 nm, or a range defined by any two of the above values. The thickness of the carbon layer is not limited to the values ​​listed here and may be other values ​​within the range. Keeping the thickness of the carbon layer according to the present disclosure within the above range is advantageous for improving lithium ion transport efficiency and for high-rate charging and discharging of the material, effectively ensuring the overall performance of the negative electrode material, ensuring the conductivity of the negative electrode material, suppressing volume expansion of the material, and maintaining the long-cycle performance of the negative electrode material.

[0089] Optionally, when the surface of the active material is coated with a carbon layer, the carbon mass content in the negative electrode material is 1.5 wt% to 10 wt%, optionally, for example, 2.0 wt% to 8.0 wt%, 4.0 wt% to 7.0 wt%, or 5.0 wt% to 6.0 wt%, such as 1.5 wt%, 4 wt%, 4.5 wt%, 5 wt%, 5.5 wt%, 6 wt%, 6.5 wt%, 7 wt%, 7.5 wt%, 8 wt%, 8.5 wt%, 9 wt%, or 10 wt%, or a range defined by any two of the above values. The carbon mass percentage is not limited to the values ​​listed here and may be other values ​​within the range.

[0090] The mass content of lithium in the negative electrode material is 3 wt% to 15 wt%, and optionally, the mass content of lithium is, for example, 4 wt% to 14 wt%, 6 wt% to 12 wt%, or 8 wt% to 10 wt%, such as 3 wt%, 3.5 wt%, 4.5 wt%, 5.5 wt%, 8 wt%, 9.5 wt%, 10.5 wt%, 12.1 wt%, 12.9 wt%, or 15 wt%, or a range defined by any two of the above values. The mass percentage of lithium is not limited to the values ​​listed here and may be other values ​​within the range. By keeping the lithium content in the negative electrode material within the above range, most of the lithium source can penetrate into the silicon-oxygen material and form a lithium silicate framework (i.e., lithium silicate 120), thereby improving the initial coulombic efficiency of the negative electrode material. Furthermore, the lithium silicate selected as described above can control the amount of lithium in the surface layer, minimizing lithium loss after surface treatment and improving utilization efficiency. It can ensure the formation of a silicate framework (i.e., water-insoluble silicate 140) through lithium doping in the surface layer of the active material. Its water-insoluble properties prevent contact between water and the strongly alkaline lithium silicate (i.e., lithium silicate 120), effectively inhibiting the hydrolysis of lithium silicate, controlling pH, and suppressing gas generation. The specific surface area of ​​the negative electrode material is 1.0 m. 2 / g~12.0m 2 / g, for example, 2.0m 2 / g~10.0m 2 / g, 3.5m 2 / g~6.0m 2 / g or 4.0m 2 / g~5.5m 2 / g, for example, 1.0m 2 / g, 1.50m 2 / g, 2.00m 2 / g, 3.00m 2 / g, 4.00m 2 / g, 5.0m 2 / g, 7.0m 2 / g, 9.0m 2 / g, 10.0m 2 / g or 12.0m 2 / g, or a range defined by any two of the above values. The specific surface area of ​​the negative electrode material is not limited to the values ​​listed here, and other values ​​within the range may be used. If the specific surface area of ​​the negative electrode material falls within the above range, the workability of the material can be ensured, which is advantageous for improving the initial coulombic efficiency of a lithium battery fabricated using the negative electrode material and for improving the cycle performance of the negative electrode material.

[0091] In an optional technical solution of the present disclosure, the average particle size of the negative electrode material is 3.0 μm to 12.0 μm, for example, 4.0 μm to 11.0 μm, 5.0 μm to 10.0 μm, or 6.0 μm to 8.0 μm, such as 3.0 μm, 4.0 μm, 6.5 μm, 7.0 μm, 8.2 μm, 9.5 μm, 10.0 μm, or 12.0 μm, or a range defined by any two of the above values. Keeping the average particle size of the negative electrode material within the above range is advantageous for improving the cycle performance of the negative electrode material. Optionally, the average particle size of the negative electrode material is 4.5 μm to 9.0 μm.

[0092] As an optional technical solution of the present disclosure, the tap density of the negative electrode material is 0.6 g / cm 3 ~1.2g / cm 3 For example, 0.7 g / cm 3 ~1.1g / cm 3 , 0.8g / cm 3 ~1.0g / cm 3 or 0.9 g / cm 3 ~1.0g / cm 3 For example, 0.6 g / cm 3 , 0.7g / cm 3 , 0.75g / cm 3 , 0.8g / cm 3 , 0.85g / cm 3 , 0.9g / cm 3 , 0.95g / cm 3 , 1.0g / cm 3 , 1.1g / cm 3 or 1.2 g / cm 3or a range defined by any two of the above values. The tap density of the negative electrode material is not limited to the values ​​listed here, and other values ​​within the range may be used. If the tap density of the negative electrode material falls within the above range, it is advantageous for improving the energy density of a lithium battery produced using the negative electrode material.

[0093] The pH value of the negative electrode material is 8.5 to 12.0, for example, 8.6 to 11.0, 9.0 to 10.5, or 9.5 to 10.0, such as 8.5, 8.8, 8.9, 9.2, 9.5, 9.8, 10.0, 10.3, 10.5, 10.8, 11.0, 12.0, etc., or a range defined by any two of the above values. By filling the carbon material with a lithium-containing compound, the alkalinity of the material can be effectively reduced, the aqueous processability of the material can be improved, and the initial coulomb efficiency of the negative electrode material can be improved.

[0094] As an optional technical solution of the present disclosure, the content of lithium element in the water-insoluble silicate of the negative electrode material is pm, and the total content of lithium element in the negative electrode material is p Li and 0.01≦pm / p Li ≦0.6. In the present disclosure, as long as the lithium content in the negative electrode material is within the above range, it is possible to ensure the formation of a stable water-insoluble silicate framework (i.e., water-insoluble silicate 140) on the surface layer of the active material, prevent contact between water and the strongly alkaline lithium silicate (i.e., lithium silicate 120), effectively inhibit the hydrolysis of the lithium silicate, realize pH control, and suppress gas generation.

[0095] In an alternative technical solution of the present disclosure, the negative electrode material is a silicon-oxygen composite material.

[0096] The preparation method according to the present disclosure will now be described in detail.

[0097] One embodiment of the present disclosure provides a method for preparing a negative electrode material, the method comprising the steps of:

[0098] S10: The prelithiated silicon-oxygen material is subjected to a surface etching treatment.

[0099] S20: The surface-etched silicon-oxygen material is mixed with a substance containing at least one of metal M and metal A (for example, at least one of metal M and metal A, or a compound containing at least one of metal M and metal A), and a solid-phase thermal reaction is carried out in a protective gas atmosphere to obtain a negative electrode material.

[0100] The negative electrode material includes an active material, the active material including a skeletal structure present throughout the active material and a silicon-oxygen material distributed in the skeletal structure, the skeletal structure including a lithium silicate framework located inside the active material and a water-insoluble silicate framework located on the surface of the active material, the water-insoluble silicate framework and the lithium silicate framework being connected to each other.

[0101] In the above scheme, the pre-lithiated silicon-oxygen material is subjected to a surface etching treatment, followed by a solid-state thermal reaction between the etched silicon-oxygen material and a metal M-containing substance, thereby forming a water-insoluble silicate on the surface of the etched silicon-oxygen material. This prevents easily soluble, strongly alkaline substances such as lithium silicate from dissolving in the slurry, effectively preventing pH loss and gas generation in the slurry. This also prevents loss of the active silicon-oxygen material and active lithium, improving the initial coulombic efficiency and capacity of the material. The lithium silicate and the water-insoluble silicate are silicates of different crystal types grown on the same silicon-oxygen framework, forming a tight heterojunction interface without forming a vacuum cross section, which is beneficial for electron transfer between the heterojunction materials, improves the ionic conductivity of the material, and enhances the rate performance of the material. Furthermore, the preparation process is simple, contributing to mass production and reducing costs. Before step S10, the preparation method further includes a step of applying a carbon coating to the silicon-oxygen material to obtain a carbon-coated silicon-oxygen material.

[0102] When a carbon coating is applied to a silicon and oxygen material, the carbon coating layer is relatively sparse and has a large number of micropore passages, so that the subsequent lithium source can pass through the micropore passages of the carbon coating layer, penetrate the carbon coating layer, and react on the surface of the silicon and oxygen material, and in the obtained negative electrode material, the carbon coating layer remains as the outermost layer.

[0103] As an optional technical solution of the present disclosure, the carbon coating includes at least one of a gas phase carbon coating and a solid phase carbon coating.

[0104] When vapor-phase carbon coating is adopted as an optional technical solution of the present disclosure, the silicon-oxygen material is heated to 600°C to 1000°C under a protective gas atmosphere, an organic carbon source gas is introduced, the temperature is maintained for 0.5 to 10 hours, and then the material is cooled.

[0105] In some embodiments, the organic carbon source gas comprises a hydrocarbon. In some embodiments, the organic carbon source comprises a hydrocarbon. In some embodiments, the hydrocarbon comprises an alkane, an olefin, an alkyne, or an aromatic hydrocarbon. In some embodiments, the hydrocarbon is a hydrocarbon that can be vaporized at 600°C to 1000°C. In some embodiments, the hydrocarbon comprises at least one of methane, ethylene, acetylene, and benzene. In some embodiments, the hydrocarbon comprises at least one organic carbon source such as methane, ethane, propane, ethylene, propylene, acetylene, benzene, or toluene.

[0106] In the case of adopting solid-phase carbon coating as an optional technical solution of the present disclosure, the material to be carbon-coated and the carbon source are fused for 0.5 to 2 hours, and then the resulting carbon mixture is carbonized at 600 to 1000°C for 2 to 6 hours, and then cooled.

[0107] In some embodiments, the carbon source comprises at least one of hard carbon, soft carbon, carbon nanotubes, nanocarbon fibers, graphite, graphene, pitch, and organic-inorganic hybrid carbon materials.

[0108] Optionally, before step S10, the preparation method further includes a step of reacting the silicon and oxygen material with a lithium source to obtain a pre-lithiated silicon and oxygen material, or a step of reacting the carbon-coated silicon and oxygen material with a lithium source to obtain a pre-lithiated carbon-coated silicon and oxygen material.

[0109] Silicon-oxygen materials are SiO n where n satisfies 0.5≦n≦1.5, and SiO n For example, SiO 0.5 , SiO 0.6 , SiO 0.7 , SiO 0.8 , SiO 0.9 , SiO, SiO 1.1 , SiO 1.2 or SiO 1.5 etc. Optionally, the silicon oxygen material is SiO.

[0110] In some embodiments, the average particle size (D50) of the silicon and oxygen material is 2.0 μm to 15.0 μm, such as 3.0 μm to 13.0 μm, 6.0 μm to 11.0 μm, or 7.0 μm to 10.0 μm, such as 2.0 μm, 3.5 μm, 4.0 μm, 4.5 μm, 5.0 μm, 5.5 μm, 6.0 μm, 7.5 μm, 9.0 μm, 10.5 μm, 12 μm, or 15.0 μm, or a range defined by any two of the above values. By keeping the average particle size of the silicon and oxygen material according to the present disclosure within the above range, the structural stability, thermal stability, and long-term cycle stability of the negative electrode material can be further ensured.

[0111] In some embodiments, the average particle size (D50) of the carbon-coated silicon / oxygen material is 2.0 μm to 15.0 μm, such as 3.0 μm to 13.0 μm, 6.0 μm to 11.0 μm, or 7.0 μm to 10.0 μm, such as 2.0 μm, 3.5 μm, 4.0 μm, 4.5 μm, 5.0 μm, 5.5 μm, 6.0 μm, 7.5 μm, 9.0 μm, 10.5 μm, 12 μm, or 15.0 μm, or a range defined by any two of the above values. The particle size is not limited to the values ​​listed here, and other values ​​within the range may also be used. Keeping the particle size of the carbon-coated silicon / oxygen material or silicon / oxygen material within the above range can prevent cycle stability issues caused by uneven distribution and type of lithium silicate product, and is advantageous for improving the structural stability, thermal stability, and long-term cycle stability of the negative electrode material.

[0112] Optionally, the thickness of the carbon layer on the surface of the carbon-coated silicon-oxygen material is 30 nm to 500 nm, e.g., 50 nm to 550 nm, 90 nm to 500 nm, 160 nm to 400 nm, or 220 nm to 300 nm, e.g., 30 nm, 50 nm, 60 nm, 70 nm, 80 nm, 90 nm, 100 nm, 150 nm, 200 nm, 300 nm, 400 nm, or 500 nm, or a range defined by any two of the above values. The thickness is not limited to the values ​​listed here and may be other values ​​within the range. If the coating layer is too thick, the lithium ion transport efficiency decreases, which is disadvantageous for high-rate charging and discharging of the material and reduces the overall performance of the negative electrode material. If the coating layer is too thin, it is disadvantageous for increasing the conductivity of the negative electrode material and also weakens the suppression of volume expansion of the material, resulting in a deterioration of long-cycle performance.

[0113] In an alternative technical solution of the present disclosure, the lithium source includes elemental lithium, a lithium-containing compound, or a mixture thereof. In an alternative technical solution of the present disclosure, the lithium source includes at least one of lithium hydride, alkyl lithium, metallic lithium, lithium aluminum hydride, lithium amide, and lithium borohydride. Optionally, the lithium source further includes a lithium-containing oxide, a lithium-containing hydride, or the like.

[0114] Optionally, in the reaction of the carbon-coated silicon-oxygen material or the silicon-oxygen material with the lithium source, the reaction temperature is 150°C to 300°C, such as 180°C to 280°C, 200°C to 260°C, or 210°C to 240°C, such as 150°C, 170°C, 180°C, 200°C, 220°C, 250°C, 280°C, or 300°C, or a range defined by any two of the above values, and the reaction time is 2.0 hours to 6.0 hours, such as 2.0 hours, 2.5 hours, 3.0 hours, 3.5 hours, 4.0 hours, 4.5 hours, 5.0 hours, 5.5 hours, or 6.0 hours, or a range defined by any two of the above values. By controlling the reaction temperature and reaction time, at least a portion of the lithium source penetrates into the interior of the silicon and oxygen material particles to form a Li—SiO material, while the majority of the lithium source deposits on the surface layer of the silicon and oxygen material and undergoes a reduction reaction with the silicon and oxygen material to produce lithium oxide or lithium hydroxide, which is then embedded in the voids in the carbon coating layer on the surface of the silicon and oxygen material.

[0115] As an optional technical solution of the present disclosure, a carbon-coated silicon-oxygen material, SiO n and the lithium source is 1:(0.01-0.20), and optionally, for example, 1:(0.02-0.18), 1:(0.04-0.16), or 1:(0.08-0.12), such as 1:0.01, 1:0.03, 1:0.05, 1:0.1, 1:0.15, 1:0.2, or a range defined by any two of the above values. The mass ratio is not limited to the values ​​listed here, and other values ​​within the range may also be used.

[0116] In an optional technical solution of the present disclosure, the mass content of lithium in the pre-lithiated carbon-coated silicon and oxygen material is 3 wt% to 20 wt%. In the present disclosure, if the lithium content in the pre-lithiated carbon-coated silicon and oxygen material is within the above range, it is possible to ensure the reliable production of a highly stable water-insoluble silicate, prevent the electrolyte from penetrating into the active material, and effectively suppress gas generation. If the lithium content in the pre-lithiated carbon-coated silicon and oxygen material is too low or too high, the silicon dioxide framework and the metal M-containing substance will react sufficiently to produce a stable water-insoluble silicate, which will prevent contact between the silicon and oxygen material, lithium silicate, and the electrolyte and will be disadvantageous in suppressing gas generation.

[0117] Optionally, the mass content of lithium in the prelithiated carbon-coated silicon-oxygen material is, for example, 4 wt% to 18 wt%, 6 wt% to 16 wt%, or 9 wt% to 14 wt%, such as 3 wt%, 5 wt%, 8 wt%, 10 wt%, 12 wt%, 15 wt%, 18 wt%, or 20 wt%, or a range defined by any two of the above values, and is not limited to the values ​​listed herein and may be other values ​​within the range.

[0118] In some embodiments, an acid pickling process is used to provide a surface etching process to the prelithiated silicon and oxygen material or the prelithiated carbon-coated silicon and oxygen material.

[0119] In an optional technical solution of the present disclosure, the acid solution used in the surface etching treatment has a property of maintaining a pH of the surface etching reaction system below 7 when the pre-lithiated silicon-oxygen material is subjected to the surface etching treatment. In an optional technical solution of the present disclosure, the acid solution used in the surface etching treatment includes at least one of hydrochloric acid, acetic acid, nitric acid, citric acid, oxalic acid, sulfuric acid, formic acid, phenol, phosphoric acid, hydrogen phosphate, hydroiodic acid, hydrobromic acid, ethylenediaminetetraacetic acid, glycolic acid, gluconic acid, and succinic acid, but is not limited to these.

[0120] As an optional technical solution of the present disclosure, the surface etching treatment time is 0.5 to 10.0 hours.

[0121] After the surface etching treatment, the surface layer of the silicon oxygen material contains no or only a small amount of lithium silicate, and the surface layer of the silicon oxygen material is mainly silicon oxygen material and also contains disproportionated silicon dioxide.

[0122] The silicon dioxide framework exposed on the surface of the surface-etched silicon-oxygen material reacts with the metal M-containing substance to produce a water-insoluble silicate.

[0123] S20: The surface-etched silicon-oxygen material is mixed with a substance containing at least one of metal M and metal A, and a solid-phase thermal reaction is carried out in a protective gas atmosphere to obtain a negative electrode material.

[0124] As an optional technical solution of the present disclosure, the metal M-containing substance includes at least one of an elemental metal M and a compound containing metal M, and the compound containing metal M includes at least one of a carbonate of metal M, an oxide of metal M, a hydroxide of metal M, and a soluble silicate of metal M. M is at least one selected from Mg, Al, Ca, Ge, Cr, Pb, Sr, Zn, Zr, Fe, and Mn. Illustratively, the metal M-containing substance may be an oxide of M, such as magnesium oxide, calcium oxide, or aluminum oxide. The metal M-containing substance may be a carbonate of metal M, such as magnesium carbonate, calcium carbonate, or aluminum carbonate.

[0125] The metal M and metal A are each selected from metal elements having an electronegativity of 1.0 to 1.9.

[0126] Optionally, the metal M-containing material is an oxide of the metal M.

[0127] In an alternative technical solution of the present disclosure, the metal A-containing substance includes at least one of metal A alone, a carbonate of metal A, an oxide of metal A, and a hydroxide of metal A, where A includes at least one of Li, Na, and K. In an alternative technical solution of the present disclosure, the metal A-containing compound includes at least one of a carbonate of metal A, an oxide of metal A, a hydroxide of metal A, and a soluble silicate of metal A. Exemplarily, the metal A-containing compound may be an oxide of metal A, such as lithium oxide, potassium oxide, or sodium oxide. The metal A-containing compound may be a carbonate of metal A, such as lithium carbonate, potassium carbonate, or sodium carbonate. For example, metal salts with relatively strong alkalinity (e.g., pH > 10), such as lithium carbonate, sodium carbonate, and potassium carbonate, may be used in combination with other substances and should not be used alone. In an optional technical solution of the present disclosure, the mass ratio of the surface-etched silicon-oxygen material to the metal M-containing substance (metal M alone or a compound containing M) is 1:(0.01-0.1), optionally 1:(0.075-0.1). In the present disclosure, if the mass ratio of M is too high, an excessive amount of insoluble and inactive MO·xSiO2 (0.2≦x≦10.0) is formed on the surface, resulting in a decrease in the reversible capacity and conductivity of the powder. If the mass ratio of M is too low, the content of the metal M-containing substance on the surface will be too low, which will prevent the metal M-containing substance from reacting sufficiently with the silicon-oxygen material, which is unfavorable for forming a water-insoluble silicate framework on the surface layer of the silicon-oxygen material. The electrolyte will easily permeate the surface of the negative electrode material and react with the lithium silicate inside the particles, which is unfavorable for suppressing the alkalinity of the material. This will result in excessive gas generation during the processing of the negative electrode material, which will reduce the initial coulombic efficiency and cycle stability of the battery.

[0128] In one alternative technical solution, the mass ratio of the surface-etched silicon-oxygen material to metal A or a compound containing metal A is 1:(0.01-0.1). Within this range, the powder can be guaranteed to have high reversible capacity and high electrical conductivity. The reaction primarily produces insoluble and inert AO·nSiO (1≦n≦10), allowing the metal A compound to fully react with the silicon-oxygen material, favoring the formation of a water-insoluble silicate framework on the surface of the silicon-oxygen material. This prevents the electrolyte from reacting with the lithium silicate inside the particles, effectively suppresses the alkalinity of the material, and prevents gas generation during processing of the negative electrode material, further improving the initial coulombic efficiency and cycle stability of the battery.

[0129] Optionally, the mass ratio of the surface-etched silicon-oxygen material to the metal M-containing material is, for example, 1:(0.020-0.095), 1:(0.040-0.090), 1:(0.060-0.085), or 1:(0.078-0.082), such as 1:0.1, 1:0.2, 1:0.3, 1:0.4, 1:0.5, 1:0.6, 1:0.7, 1:0.075, 1:0.081, 1:0.083, 1:0.085, 1:0.087, 1:0.091, 1:0.093, 1:0.095, or 1:0.1, or a range defined by any two of the above values. It is not limited to the values ​​listed here, and other values ​​within the range may also be used.

[0130] Optionally, the mass ratio of the surface-etched silicon-oxygen material to the metal A or the metal A-containing compound is, for example, 1:(0.020-0.095), 1:(0.040-0.090), 1:(0.060-0.085), or 1:(0.078-0.082), such as 1:0.1, 1:0.2, 1:0.3, 1:0.4, 1:0.5, 1:0.6, 1:0.7, 1:0.075, 1:0.081, 1:0.083, 1:0.085, 1:0.087, 1:0.091, 1:0.093, 1:0.095, or 1:0.1, or a range defined by any two of the above values. The mass ratio is not limited to the values ​​listed here, and other values ​​within the range may also be used.

[0131] In the present disclosure, the mixing method may include at least one of mechanical stirring, ultrasonic dispersion, and abrasive dispersion. Of course, the mixing method is not limited to the above methods, and any method that can uniformly mix the pre-lithiated silicon-oxygen material and the metal M-containing substance may be used.

[0132] Optionally, the mixing method is ball milling, and the ball milling time is 3 to 24 hours, for example, 6 to 21 hours, 9 to 17 hours, or 11 to 15 hours, such as 3, 4, 5, 6, 8, 12, 16, 18, 20, or 24 hours, or a range defined by any two of the above values. The values ​​are not limited to those listed here, and other values ​​within the range may also be used. Furthermore, sufficient ball milling can ensure that the metal M-containing substance adheres uniformly to the surface of the surface-etched silicon / oxygen material or the surface of the surface-etched carbon-coated silicon / oxygen material.

[0133] As an optional technical solution of the present disclosure, the protective gas includes at least one of nitrogen gas, helium gas, neon gas, argon gas, krypton gas, and xenon gas.

[0134] In some embodiments, the solid-state thermal reaction is a calcination process, and to ensure sufficient calcination, the calcination can be carried out in a kiln.

[0135] Optionally, the solid-state thermal reaction temperature is 600°C to 1200°C, such as 640°C to 1160°C, 720°C to 920°C, or 780°C to 820°C, such as 600°C, 700°C, 750°C, 800°C, 850°C, 900°C, 950°C, 1000°C, 1050°C, 1100°C, or 1200°C, or a range defined by any two of the above values. The reaction temperature is not limited to the values ​​listed here and may be other values ​​within the range. Optionally, the reaction temperature is 750°C to 1150°C. Note that if the reaction temperature is too high, the reaction will be too vigorous, causing rapid growth of silicon crystal grains and affecting the cycle performance of the material. If the reaction temperature is too low, the water-insoluble silicate framework on the surface of the surface-etched silicon / oxygen material will not be formed.

[0136] Optionally, the solid-state thermal reaction time may be 3 to 12 hours, such as 5 to 11 hours, 6 to 9 hours, or 7 to 8 hours, such as 3, 4, 5, 6, 7, 8, 9, 10, 11, or 12 hours, or a range defined by any two of the above values. The values ​​are not limited to those listed here, and other values ​​within the range may also be used. Furthermore, sufficient calcination can produce a water-insoluble silicate framework on the surface of the surface-etched silicon / oxygen material.

[0137] Optionally, the heating rate of the solid-state thermal reaction is 1°C / min to 5°C / min, such as 1°C / min, 2°C / min, 3°C / min, 4°C / min, or 5°C / min, or a range defined by any two of the above values. It is not limited to the values ​​listed here and may be other values ​​within the range.

[0138] During the solid-state thermal reaction, the metal M-containing material reacts with the silicon dioxide framework exposed on the surface of the surface-etched silicon-oxygen material through disproportionation and the strongly alkaline lithium silicate to form a water-insoluble silicate framework, preventing the electrolyte from easily penetrating the surface of the negative electrode material and reacting with the lithium silicate inside the particles, lowering the pH of the material and thereby adjusting the pH of the entire negative electrode slurry, thereby improving the processing stability of the pre-lithiated material and improving the initial coulombic efficiency of the negative electrode material.

[0139] Optionally, after step S20, the method further includes the following steps:

[0140] The negative electrode material obtained by the solid-state thermal reaction is cooled and sieved to have an average particle size of 1 μm to 10 μm. The average particle size is, for example, 2.5 μm to 9.5 μm, 3.5 μm to 7 μm, or 4.5 μm to 6.5 μm, such as 1 μm, 2 μm, 3 μm, 4 μm, 6 μm, 7 μm, 8 μm, 9 μm, or 10 μm, or a range defined by any two of the above values. Keeping the average particle size of the negative electrode material within the above range is advantageous for improving the cycle performance of the negative electrode material. Optionally, the average particle size of the negative electrode material is 4 μm to 7 μm.

[0141] In some embodiments, sieving comprises at least one of crushing, ball milling, screening, or classifying.

[0142] The negative electrode material prepared by the above method has a waterproof layer composed of a water-insoluble silicate framework and an embedded silicon-oxygen material, which prevents the reaction between the strongly alkaline material and the solvent, suppresses gas generation, and minimizes the impact on the capacity and initial coulombic efficiency of the material, allowing the pH value of the negative electrode slurry prepared using this material to be controlled. The active silicon-oxygen material is embedded in the silicate framework and the lithium silicate framework, and the resulting framework structure serves as a stable expansion buffer, allowing nano-silicon crystal grains to be embedded throughout the entire particle system, ensuring good contact between the silicon-oxygen material and the conductive carbon layer, improving conductivity, reducing interfacial resistance, and ensuring the stability of the conductive channels and lithium ion transport channels within the particles.

[0143] As shown in Figure 1, one embodiment of the present disclosure provides a method for preparing a negative electrode material, which includes the following steps:

[0144] S100: The prelithiated silicon-oxygen material is subjected to a surface etching treatment.

[0145] S200: The surface-etched silicon-oxygen material is mixed with a compound containing metal M, and a solid-state thermal reaction is carried out in a protective gas atmosphere to obtain a negative electrode material.

[0146] In some embodiments, the surface-etched silicon-oxygen material can be further mixed with a substance containing metal A. Metal A comprises an alkali metal element, and optionally, metal A comprises at least one of Li, Na, and K.

[0147] The present disclosure provides a lithium-ion battery comprising an anode material according to the first aspect above or an anode material prepared by the preparation method according to the second aspect above.

[0148] The negative electrode material disclosed herein has a silicon-oxygen material embedded in the framework, connecting the water-insoluble silicate framework of the outer layer with the lithium silicate framework of the inner layer. This is beneficial for the electrochemical performance of the active material, accelerating electron transfer and lithium intercalation / deintercalation, lowering the internal resistance of the material, and improving lithium ion mobility. By covering the silicon-oxygen material with the water-insoluble silicate framework formed in the outer layer, contact between water and the strongly alkaline lithium silicate can be effectively prevented, suppressing the hydrolysis of the lithium silicate. This effectively reduces gas generation in the material, allows control over the pH of the material, and improves processability. The lithium silicate of the inner layer and the water-insoluble silicate of the outer layer are tightly connected to the silicon and silicon-oxygen material. Due to the difference in work functions between the two silicate materials, a heterojunction interface is formed between them, increasing the efficiency of electron transfer at the junction interface, thereby improving the depth of lithium intercalation and capacity and cycle performance.

[0149] In addition, the method for preparing a negative electrode material according to the present disclosure involves surface etching a prelithiated silicon-oxygen material and then subjecting the etched silicon-oxygen material to a solid-state thermal reaction with a metal M-containing substance, thereby forming a water-insoluble silicate on the surface of the etched silicon-oxygen material. This prevents easily soluble, strongly alkaline substances such as lithium silicate from dissolving in the slurry, effectively preventing pH loss and gas generation in the slurry. This also prevents loss of active silicon-oxygen material and active lithium, improving the initial coulombic efficiency and capacity of the material. The lithium silicate and the water-insoluble silicate are silicates of different crystal types grown on the same silicon-oxygen framework, forming a tight heterojunction interface without forming a vacuum cross section, which is beneficial for electron transfer between the heterojunction materials, improves the ionic conductivity of the material, and enhances the rate performance of the material. Furthermore, the preparation process is simple, contributing to mass production and reducing costs.

[0150] Example

[0151] The present disclosure will be further described below with reference to several examples. The present disclosure is not limited to the following examples. It can be modified and implemented as appropriate within the scope of protection.

[0152] Example 1

[0153] (1) The carbon-coated silicon-oxygen material SiO / C was reacted with metallic lithium to obtain a prelithiated carbon-coated silicon-oxygen material Li~SiO / C, with a lithium content of 10 wt%.

[0154] (2) The prelithiated material was immersed in a 10 wt% citric acid solution for 1 h, surface etched, and then suction filtered and dried in a dry environment at 80°C for 24 h.

[0155] (3) Magnesium oxide (5 g) and surface-etched pre-lithiated silicon suboxide (100 g) were placed in a ball mill and ball milled for 12 hours. After that, the mixture was placed in a graphite crucible and treated at 850°C for 10 hours under a protective gas atmosphere. The mixture was then crushed, sieved, and classified to obtain the negative electrode material.

[0156] FIG. 3 is a schematic diagram of the negative electrode material prepared in this example. As shown in FIG. 3, the negative electrode material includes an active material 100 and a carbon layer (i.e., coating layer 200) formed on the surface of the active material. The active material 100 includes a framework structure and a silicon-oxygen material embedded in the framework structure. The framework structure includes a lithium silicate framework (i.e., lithium silicate 120) located inside the active material and a magnesium silicate framework (i.e., water-insoluble silicate 140) located on the surface layer of the active material, and the magnesium silicate framework (water-insoluble silicate 140) is connected to the lithium silicate framework. In this example, the lithium silicate framework (i.e., lithium silicate 120) was Li2SiO5, Li2SiO3, or Li4SiO4, and the surface layer of the active material (i.e., water-insoluble silicate 140) was Mg2SiO4 and Li2MgSiO4.

[0157] The negative electrode material has an average particle size (D50) of 5.0 μm and a tap density of 0.98 g / cm 3 and the specific surface area is 2.54m 2 / g, the mass content of lithium in the negative electrode material was 9.5 wt %, and the thickness of the carbon layer was 183 nm.

[0158] Example 2

[0159] (1) The carbon-coated silicon-oxygen material SiO / C was reacted with metallic lithium to obtain a prelithiated carbon-coated silicon-oxygen material Li~SiO / C, with a lithium content of 10 wt%.

[0160] (2) The prelithiated material was immersed in a 10 wt% citric acid solution for 1 h, surface etched, and then suction filtered and dried in a dry environment at 80°C for 24 h.

[0161] (3) Magnesium oxide (2.5 g), lithium carbonate (4.6 g), and surface-etched pre-lithiated silicon suboxide (100 g) were placed in a ball mill and ball milled for 12 hours. The mixture was then placed in a graphite crucible and treated at 850°C for 10 hours in a protective gas atmosphere. The mixture was then crushed, sieved, and classified to obtain the negative electrode material.

[0162] FIG. 3 is a schematic diagram of the negative electrode material prepared in this example. As shown in FIG. 3, the negative electrode material includes an active material 100 and a carbon layer (i.e., coating layer 200) formed on the surface of the active material. The active material 100 includes a framework structure and a silicon-oxygen material embedded in the framework structure. The framework structure includes a lithium silicate framework (i.e., lithium silicate 120) located inside the active material and a lithium magnesium silicate framework (i.e., water-insoluble silicate 140) located on the surface layer of the active material, and the lithium magnesium silicate framework (water-insoluble silicate 140) is connected to the lithium silicate framework. In this example, the lithium silicate framework (i.e., lithium silicate 120) was Li2SiO5, Li2SiO3, or Li4SiO4, and the surface layer of the active material (i.e., water-insoluble silicate 140) was Li2MgSiO4.

[0163] The negative electrode material prepared in this example had an average particle size (D50) of 5.0 μm and a tap density of 0.98 g / cm 3 and the specific surface area is 2.54m 2 / g, the mass content of lithium in the negative electrode material was 9.5 wt %, and the thickness of the carbon layer was 183 nm.

[0164] Example 3

[0165] (1) The carbon-coated silicon-oxygen material SiO / C was reacted with metallic lithium to obtain a prelithiated carbon-coated silicon-oxygen material Li~SiO / C, with a lithium content of 10 wt%.

[0166] (2) The prelithiated material was immersed in a 10 wt% citric acid solution for 1 h, surface etched, and then suction filtered and dried in a dry environment at 80°C for 24 h.

[0167] (3) Magnesium powder (3 g) and surface-etched pre-lithiated silicon suboxide (100 g) were placed in a ball mill and ball milled for 12 hours in an inert atmosphere. The mixture was then placed in a graphite crucible and treated at 850°C for 10 hours in a protective gas atmosphere. The mixture was then crushed, sieved, and classified to obtain the negative electrode material.

[0168] FIG. 3 is a schematic diagram of the negative electrode material prepared in this example. As shown in FIG. 3, the negative electrode material includes an active material 100 and a carbon layer (i.e., coating layer 200) formed on the surface of the active material. The active material 100 includes a framework structure and a silicon-oxygen material embedded in the framework structure. The framework structure includes a lithium silicate framework (i.e., lithium silicate 120) located inside the active material and a magnesium silicate framework (i.e., water-insoluble silicate 140) located on the surface layer of the active material, and the magnesium silicate framework (water-insoluble silicate 140) is connected to the lithium silicate framework. In this example, the lithium silicate framework (i.e., lithium silicate 120) was Li2SiO5, Li2SiO3, or Li4SiO4, and the surface layer of the active material (i.e., water-insoluble silicate 140) was Mg2SiO4, MgSiO3, or Li2MgSiO4.

[0169] The negative electrode material prepared in this example had an average particle size (D50) of 5.0 μm and a tap density of 0.98 g / cm 3 and the specific surface area is 2.54m 2 / g, the mass content of lithium in the negative electrode material was 9.5 wt%, and the thickness of the carbon layer was 183 nm. The XRD diffraction pattern of the negative electrode material prepared in this example is shown in Figure 6.

[0170] Example 4

[0171] Step (1) was similar to Example 1, differing only in that the lithium content was 11 wt%.

[0172] Step (2) was similar to Example 1, except that the prelithiated material was immersed in a 12 wt % acetic acid solution for 1.2 hours.

[0173] In step (3), Al2O3 (7.5 g) and surface-etched pre-lithiated silicon suboxide (100 g) were placed in a ball mill and milled for 10 hours. The mixture was then placed in a graphite crucible and treated at 850 °C for 10 hours under a protective gas atmosphere. The mixture was then crushed, sieved, and classified to obtain the negative electrode material.

[0174] FIG. 3 is a schematic diagram of the negative electrode material prepared in this example. As shown in FIG. 3, the negative electrode material includes an active material 100 and a carbon layer (i.e., coating layer 200) formed on the surface of the active material. The active material 100 includes a framework structure and a silicon-oxygen material embedded in the framework structure. The framework structure includes a lithium silicate framework (i.e., lithium silicate 120) located inside the active material and a lithium aluminum silicate framework (i.e., water-insoluble silicate 140) located on the surface layer of the active material, and the lithium aluminum silicate framework (water-insoluble silicate 140) is connected to the lithium silicate framework. In this example, the lithium silicate framework (i.e., lithium silicate 120) was Li2SiO2O5, Li2SiO3, and Li4SiO4, and the surface layer of the active material (i.e., water-insoluble silicate 140) was Al2SiO5, LiAlSiO4, LiAlSi2O6, and LiAlSi3O8.

[0175] The negative electrode material prepared in this example had an average particle size (D50) of 5.0 μm and a tap density of 0.98 g / cm 3 and the specific surface area is 2.77m 2 / g, the mass content of lithium in the negative electrode material was 9.6 wt %, and the thickness of the carbon layer was 177 nm.

[0176] Example 5

[0177] Step (1) was similar to Example 1, differing only in that the lithium content was 11 wt%.

[0178] Step (2) is similar to Example 1, except that the prelithiated material was immersed in a 1 wt % nitric acid solution for 0.5 h.

[0179] In step (3), Na2CO3 (8 g) and surface-etched pre-lithiated silicon suboxide (100 g) were placed in a ball mill and milled for 10 hours. The mixture was then placed in a graphite crucible and treated at 850 °C for 10 hours under a protective gas atmosphere. The mixture was then crushed, sieved, and classified to obtain the negative electrode material.

[0180] FIG. 3 is a schematic diagram of the negative electrode material prepared in this example. As shown in FIG. 3, the negative electrode material includes an active material 100 and a carbon layer (i.e., coating layer 200) formed on the surface of the active material. The active material 100 includes a framework structure and a silicon-oxygen material embedded in the framework structure. The framework structure includes a lithium silicate framework (i.e., lithium silicate 120) located inside the active material and a sodium lithium silicate framework (i.e., water-insoluble silicate 140) located on the surface layer of the active material, and the sodium lithium silicate framework (water-insoluble silicate 140) is connected to the lithium silicate framework. In this example, the lithium silicate framework (i.e., lithium silicate 120) was Li2SiO5, Li2SiO3, and Li4SiO4, and the surface layer of the active material (i.e., water-insoluble silicate 140) was LiNaSiO4.

[0181] The negative electrode material prepared in this example had an average particle size (D50) of 5.0 μm and a tap density of 1.00 g / cm 3 and the specific surface area is 2.79m 2 / g, the mass content of lithium in the negative electrode material was 10.0 wt %, and the thickness of the carbon layer was 193 nm.

[0182] Example 6

[0183] Step (1) is similar to Example 1, except that the silicon-oxygen material SiO 2 with a silicon content of 65% is used. 0.75 / C as a carbon-coated silicon-oxygen material is reacted with metallic lithium to obtain a prelithiated carbon-coated silicon-oxygen material Li~SiO 0.75 / C was obtained, and the lithium content was 10 wt%.

[0184] The other steps were the same as in Example 1.

[0185] FIG. 3 is a schematic diagram of the negative electrode material prepared in this example. As shown in FIG. 3, the negative electrode material includes an active material 100 and a carbon layer (i.e., coating layer 200) formed on the surface of the active material. The active material 100 includes a framework structure and a silicon-oxygen material embedded in the framework structure. The framework structure includes a lithium silicate framework (i.e., lithium silicate 120) located inside the active material and a magnesium silicate framework (i.e., water-insoluble silicate 140) located on the surface layer of the active material, and the magnesium silicate framework (water-insoluble silicate 140) is connected to the lithium silicate framework. In this example, the lithium silicate framework (i.e., lithium silicate 120) was Li2SiO5, Li2SiO3, or Li4SiO4, and the surface layer of the active material (i.e., water-insoluble silicate 140) was Mg2SiO4, MgSiO3, or Li2MgSiO4.

[0186] The negative electrode material prepared in this example had an average particle size (D50) of 5.0 μm and a tap density of 1.1 g / cm 3 and the specific surface area is 2.47m 2 / g, the mass content of lithium in the negative electrode material was 9.5 wt %, and the thickness of the carbon layer was 187 nm.

[0187] Example 7

[0188] (1) The carbon-coated silicon-oxygen material SiO / C was reacted with metallic lithium to obtain a prelithiated carbon-coated silicon-oxygen material Li~SiO / C, with a lithium content of 10 wt%.

[0189] (2) The prelithiated material was immersed in a 10 wt% citric acid solution for 1 h, surface etched, and then suction filtered and dried in a dry environment at 80°C for 24 h.

[0190] (3) Magnesium oxide (5 g) and surface-etched pre-lithiated silicon suboxide (100 g) were placed in a ball mill and ball milled for 12 hours. After that, the mixture was placed in a graphite crucible and treated at 550°C for 10 hours under a protective gas atmosphere. The mixture was then crushed, sieved, and classified to obtain the negative electrode material.

[0191] The negative electrode material prepared according to this example comprises a mixture of active material and magnesium oxide.

[0192] The negative electrode material prepared in this example had an average particle size (D50) of 5.0 μm and a tap density of 0.98 g / cm 3 and the specific surface area is 2.54m 2 / g, the mass content of lithium in the negative electrode material was 9.5 wt %, and the thickness of the carbon layer was 183 nm.

[0193] Example 8

[0194] (1) The carbon-coated silicon-oxygen material SiO / C was reacted with metallic lithium to obtain a prelithiated carbon-coated silicon-oxygen material Li~SiO / C, with a lithium content of 10 wt%.

[0195] (2) The prelithiated material was immersed in a 10 wt% citric acid solution for 1 h, surface etched, and then suction filtered and dried in a dry environment at 80°C for 24 h.

[0196] (3) Magnesium oxide (0.5 g) and surface-etched pre-lithiated silicon suboxide (100 g) were placed in a ball mill and ball milled for 12 hours in an inert atmosphere. The mixture was then placed in a graphite crucible and treated at 850°C for 10 hours in a protective gas atmosphere. The mixture was then crushed, sieved, and classified to obtain the negative electrode material.

[0197] The negative electrode material prepared according to this example comprises a mixture of active material and magnesium oxide.

[0198] The negative electrode material prepared in this example had an average particle size (D50) of 5.0 μm and a tap density of 0.98 g / cm 3 and the specific surface area is 2.54m 2 / g, the mass content of lithium in the negative electrode material was 9.5 wt %, and the thickness of the carbon layer was 183 nm.

[0199] Example 9

[0200] Steps (1) and (2) were the same as in Example 8.

[0201] Step (3) was similar to that of Example 8, except that the amount of magnesium oxide added was 11 g.

[0202] The negative electrode material prepared according to this example comprises a mixture of active material and magnesium oxide.

[0203] The negative electrode material prepared in this example had an average particle size (D50) of 5.0 μm and a tap density of 0.89 g / cm 3 and the specific surface area is 3.2m 2 / g, the mass content of lithium in the negative electrode material was 9.2 wt %, and the thickness of the carbon layer was 187 nm.

[0204] Example 10

[0205] The preparation method is similar to that of Example 1, except that in step (1), a silicon-oxygen material SiO is reacted with metallic lithium to obtain a pre-lithiated silicon-oxygen material Li-SiO.

[0206] The negative electrode material has an average particle size (D50) of 5.0 μm and a tap density of 0.98 g / cm 3 and the specific surface area is 3.01m 2 / g, the mass content of lithium in the negative electrode material was 10 wt %, and there was no carbon layer.

[0207] Example 11

[0208] The preparation method was similar to that of Example 1, except that in step (2), the sample was immersed in a citric acid solution for 30 minutes.

[0209] The negative electrode material has an average particle size (D50) of 5.0 μm and a tap density of 0.98 g / cm 3 and the specific surface area is 2.74m 2 / g, the mass content of lithium in the negative electrode material was 9.5 wt %, and the thickness of the carbon layer was 189 nm.

[0210] Comparative Example 1

[0211] A prelithiated carbon-coated silicon-oxygen material, SiO-Li / C, was used as the negative electrode material, with an average particle size (D50) of 5.14 μm and a tap density of 0.98 g / cm. 3 and the specific surface area is 3.24m 2 / g and the carbon content was 5.0 wt%.

[0212] Comparative Example 2

[0213] A solution of 11.9 g of MgCl (molar mass corresponding to 5 g of MgO) was dissolved in 500 ml of purified water. After complete dissolution, 100 g of SiO-Li / C (Comparative Example 1) was added to the solution and thoroughly stirred for 10 minutes. After stirring, the solution was further subjected to suction filtration to separate the solvent. The resulting SiO-Li / Mg(OH) / C was placed in a box furnace and subjected to high-temperature treatment at 800 °C for 6 hours under the protection of Ar gas. The material was then crushed and classified to obtain a negative electrode material.

[0214] MgCl2 is formed as a magnesium hydroxide colloid or precipitate in an alkaline environment, uniformly coating the exterior of the carbon-coated prelithiated material SiO-Li / C powder. During the sintering process, some of the MgO may react with SiO2 and other silicate frameworks to produce magnesium-containing silicates, while other MgO uniformly coats the entire core. Thus, an MgO coating layer and a carbon coating layer on the outermost surface are formed, forming a multi-layered core-shell structure.

[0215] The negative electrode material prepared in this comparative example had an average particle size (D50) of 5.17 μm and a tap density of 0.98 g / cm 3 and the specific surface area is 3.40m 2 / g, the porosity was 2.17 wt%, and the carbon content was 5.0 wt%.

[0216] Measurement method

[0217] 1. Electrical performance measurements

[0218] The negative electrode materials obtained in Examples 1 to 11 (S1 to S11) and Comparative Examples 1 to 2 (R1 to R2) were used as negative electrode active materials, and artificial graphite was uniformly mixed in a mass ratio of SiO:graphite:CMC:SBR:SP:KS-6=9.2:82.8:2:2:2:2. The mixture was then applied to a copper foil current collector and dried to obtain a negative electrode plate.

[0219] First, coin-cell battery measurements were performed on the obtained electrode plates. The batteries were assembled in an argon-filled glove box. Metallic lithium pieces were used as the negative electrode, 1 mol / L LiPF6+EC+EMC was used as the electrolyte, and a polyethylene / polypropylene composite microporous film was used as the separator. Electrochemical performance was evaluated using a battery measurement device. The battery capacity was set to a standard capacity of 480 mAh / g, and charge / discharge measurements were performed at charge / discharge voltages of 0.01 to 1.5 V and a charge / discharge rate of 0.1 C. The initial reversible capacity, initial charge capacity, and initial discharge capacity were obtained. Initial Coulombic efficiency = initial discharge capacity / initial charge capacity.

[0220] After 50 cycles, the thickness H1 of the electrode plate of the lithium-ion battery was measured using a micrometer, and the electrode plate expansion rate after 50 cycles was found to be (H1-H0) / H0 x 100 wt%.

[0221] After 50 cycles, the discharge capacity was recorded as the remaining capacity of the lithium-ion battery. Capacity retention rate = remaining capacity / initial capacity * 100%.

[0222] 2.Method for measuring the average particle size of negative electrode materials

[0223] 2. Particle size measurement

[0224] Particle size measurements were performed on the negative electrode material using a Malvern Mastersizer 2000 laser particle sizer to obtain the average particle size.

[0225] 3.Method for measuring the specific surface area of ​​negative electrode materials

[0226] The specific surface area of ​​the negative electrode material was measured using a Micromeritics Tristar 3020 specific surface area and pore distribution analyzer. A specified mass of powder was taken and completely degassed under vacuum heating to remove small molecules of gas physically adsorbed on the surface. The specific surface area of ​​the particles was then calculated based on the amount of nitrogen gas adsorbed using the nitrogen gas adsorption method.

[0227] 4. Measurement of porosity of negative electrode material

[0228] The porosity of the negative electrode material was measured using a gas displacement method. Calculation method: The percentage of voids relative to the total area of ​​the sample was calculated as P = (V0 - V) / V0 * 100 wt%, where V0 is the volume of the material in its natural state, or called the apparent volume, and its unit is cm 3 or m 3 and V is the true volume of the material, in cm 3 or m 3 is.

[0229] 5. Measurement of tap density of negative electrode material

[0230] The national standard GB / T5162-2006 "Measurement of tapped density of metal powders" was followed.

[0231] 6. Measurement of carbon content in negative electrode materials

[0232] A sample of anode material was heated to high temperatures in a high-frequency furnace under oxygen-rich conditions, oxidizing carbon to carbon dioxide. The resulting gas then entered an appropriate absorption cell, absorbed the corresponding infrared radiation, and was converted into a corresponding signal by a detector. This signal was sampled by a computer and linearly corrected to convert it into a value directly proportional to the carbon dioxide concentration. The values ​​throughout the analysis were then accumulated. After the analysis was completed, the computer divided this accumulated value by the weight, multiplied by a correction factor, and subtracted the blank to obtain the percentage carbon content of the sample. Measurements were performed on the samples using a high-frequency infrared carbon and sulfur analyzer (model: Shanghai Dekai HCS-140).

[0233] 7. Measurement of lithium content in aqueous negative electrode material solution

[0234] A sample of the negative electrode material was immersed in deionized water (the ratio of material to water was 50 wt%), stirred and left to stand for 24 hours, and after separation occurred in the material liquid, the supernatant liquid was taken and subjected to ICP measurement to obtain the lithium content.

[0235] 8. XRD Measurement of Anode Materials

[0236] XRD measurements were carried out directly on the negative electrode material samples.

[0237] 9. Band gap measurement of negative electrode materials

[0238] The spectrum of the negative electrode material sample was directly obtained by UV-visible spectroscopy, and then the extremum wavelength was obtained by integrating the spectrum curve, and the band gap of the negative electrode material was obtained by the formula Eg=1240 / λ.

[0239] 10. pH measurement

[0240] The pH value was that of the slurry.

[0241] 11. Gas generation measurement

[0242] To measure gas generation, after the slurry was prepared, 4 ml of the slurry was extracted using a sealed syringe (a small syringe with a capacity of 10 ml), and after 8 hours, the change in volume inside the syringe due to gas generation (change in the syringe's scale alignment position) was observed.

[0243] 12.Measuring method for lithium element

[0244] (i) The lithium element content (expressed in pm) in the water-insoluble silicate in the negative electrode material was measured. The measurement method was as follows.

[0245] Approximately 0.5 g of a sample of the negative electrode material was taken and placed in a platinum crucible, and burned at 750°C for 2 hours. After the carbon had completely burned, an additional 4 mL of HNO3 was added. After the reaction between the acid and the sample had stabilized, the platinum crucible was placed on a hot plate at 350°C and heated until the hydrofluoric acid had evaporated and no white smoke was emitted. After the crucible had cooled, an additional 6 mL of HCl was added and heated until the residue had completely dissolved. The volume was then measured using a 100 mL plastic measuring flask, and the lithium concentration was determined.

[0246] (ii) The total lithium content in the negative electrode material (p Li The measurement method was similar to the above method (i), in which 6 mL of HF was added simultaneously with the addition of HNO3, and 4 mL of HNO3 and 6 mL of HF were mixed and reacted.

[0247] [Table 1] [Table 2]

[0248] As shown in Tables 1, 2, and Figures 4 and 5, the negative electrode materials of Examples 1 to 3 each have a silicon-oxygen material embedded in the framework, connecting the water-insoluble silicate framework of the outer layer with the lithium silicate framework inside. This is beneficial for the electrochemical performance of the active material, accelerating electron transfer and lithium intercalation / deintercalation, lowering the internal resistance of the material, and improving the lithium ion mobility. By covering the silicon-oxygen material with the water-insoluble silicate framework formed in the outer layer, contact between water and the strongly alkaline lithium silicate can be effectively prevented, suppressing the hydrolysis of the lithium silicate. This effectively improves gas generation in the material and allows for control of the pH of the material. Lithium ions can be conducted through the framework and the silicon-oxygen material on the surface of the active material, improving the ionic conductivity of the material and favoring the rate performance of the material. For a comparison of performance data between some Examples and Comparative Examples, see Figures 4 to 6.

[0249] In Example 1, a stable heterojunction interface was formed by in situ growth of water-insoluble silicate and lithium silicate on the SiO2 framework, improving the conductivity of the material, reaching 40.21 S / cm.

[0250] In Example 2, a magnesium oxide material was used, and ball milling and solid-state reaction were performed to react with the SiO2 outer layer and the strongly alkaline lithium silicate outer layer to produce an insoluble magnesium silicate salt (or lithium magnesium silicate). The work function of the lithium magnesium silicate was relatively close to that of the lithium silicate, and the powder conductivity of the material was 20.97 S / cm, which was somewhat lower than that of Example 1, but was better in terms of rate, improving by approximately 1.5% to 2.0% over Comparative Example 1 at each rate. This indicates that the improved conductivity due to the heterojunction can promote rate improvement.

[0251] In Example 3, magnesium powder was used, and a redox reaction occurred on the surface to produce MgO and SiO2, which improved the capacity and initial coulomb efficiency. The water-insoluble silicate (magnesium silicate) produced by the reaction of MgO and SiO2 could isolate the slurry from the strongly alkaline silicate. However, because the SiO2 skeleton was reduced by Mg, some of the silicon-oxygen material extending through the lithium silicate was destroyed, and part of the surface of the material particle formed a tight water-insoluble silicate interface. Therefore, the powder conductivity in Example 3 was slightly lower than that in Example 1. As can be seen from the XRD data (FIG. 6) in Example 3, when the composite anode material contains only the three components of Si / lithium silicate / magnesium silicate, a trace amount of magnesium silicate is concentrated on the surface of the composite anode material particles, as can be seen from the lithium content in the eluate, and a heterojunction structure is formed at the interface of the new silicates. Therefore, the powder conductivity in this case is much higher than that of the lithium silicate / silicon and magnesium silicate / silicon samples (0.1-10 S / cm), respectively, which indicates that the heterojunction structure on the surface of the composite anode material particles can contribute to improving the conductivity.

[0252] As can be seen from the UV-vis evaluation results for each of Examples 1 to 3, the band gaps for Examples 1, 2, and 3 are 0.63 eV, 0.78 eV, and 0.73 eV, respectively. In other words, the heterojunction effect can improve the conductivity by changing the energy band, and the formed heterojunction can contribute to improving the electrochemical performance of the material.

[0253] In Example 4, Al2O3 was used, and in Example 5, Na2CO3 was used. In each case, a water-insoluble silicate and lithium silicate were formed in situ on the silicon oxide, forming a stable heterojunction interface. Again, this improved the electrochemical performance of the material. In Example 6, a silicon-oxygen material with a silicon content of 65% was used, and magnesium oxide was used. A water-insoluble silicate and lithium silicate were also grown in situ on the silicon oxide, forming a stable heterojunction interface, resulting in a negative electrode material with high electrochemical performance. As can be seen from Examples 1 to 9 and Comparative Examples 1 and 2, the intensity of the strongest characteristic diffraction peak of soluble lithium silicate was compared with the intensity of the strongest characteristic diffraction peak of a water-insoluble silicate (e.g., magnesium silicate) by XRD, and the I in Examples 1 to 9 was obtained. B / I A The values ​​of σ are within the range of the present disclosure, resulting in higher electrochemical performance relative to the comparative examples.

[0254] Also, I B / I A When I is 0.10 or more, the content of soluble lithium (lithium element that can be naturally dissolved after the negative electrode material is put into water) in the negative electrode material is significantly reduced, and a stable water-insoluble silicate has already been formed on the outer layer of the negative electrode material, so that gas generation in the negative electrode material can be more effectively suppressed. B / I A is 0.12≦I B / I A≦0.18. The deposition of water-insoluble silicates (e.g., magnesium silicate) on the surface weakens the heterojunction interface effect, reducing the powder conductivity, which is closer to that of water-insoluble silicates (e.g., magnesium silicate), and thus affecting the electrochemical performance of the material.

[0255] In Comparative Example 1, a common pre-lithiated material was used, and the powder conductivity of the material was relatively low. This is because silicon-based materials and lithium silicate are insulators or semiconductors, and have poor conductivity when used as cell materials. Evaluation of the powder conductivity showed that the powder conductivity was 7.21 S / cm, while the powder conductivity of common graphite anode materials was 250 S / cm or more. Even with a conductive carbon coating on the surface, there was a significant difference in conductivity compared to the graphite anode material.

[0256] In Comparative Example 2, the carbon surface of the particles was coated with a magnesium oxide coating layer by the growth method, and the magnesium oxide coating layer grew on the outer layer of the conductive layer, covering the conductive carbon layer. This suppressed contact between the conductive carbon layer structure and the conductive agent, resulting in a significant decrease in powder conductivity (0.37 S / cm). Furthermore, the capacity retention rates of the batteries prepared using this material at rates of 0.5 C, 1 C, and 2 C were each 3% or more lower than those of Comparative Example 1.

[0257] In comparison with Example 7, Examples 1 to 6 of the present disclosure demonstrate that, when the treatment temperature is within the range of the present disclosure, efficient reaction between the surface-etched silicon-oxygen material and the M- or A-containing compound can be effectively ensured, the pH of the material can be controlled, gas generation can be prevented, and the powder conductivity and rate performance are effectively improved, indicating the formation of a more stable heterojunction structure. In Example 7, the treatment temperature was relatively low, which slowed the reaction between the surface lithium silicate, the SiO2 framework, and the magnesium oxide, resulting in gas generation. However, the amount of gas generated was significantly lower than in the comparative example, resulting in an increase in powder conductivity compared to the comparative example and a decrease in rate performance compared to Example 1, indicating the formation of a heterojunction structure.

[0258] The cycle capacity retention rate of the battery is also related to the heterojunction structure of the negative electrode material. As shown in Figure 4, in Examples 1 and 2, which had good conductivity, the capacity retention rate at 50 cycles was 90% or higher. In contrast, in Comparative Example 1, which did not have a heterojunction structure, the capacity retention rate at 50 cycles was reduced by about 10%. In Comparative Example 2, the surface was coated with magnesium oxide, which reduced the conductivity, preventing the battery from achieving full capacity and reducing the electrochemical performance.

[0259] As can be seen from the data on the Li concentration in the solutions of the materials of the Examples and Comparative Examples, the three samples of Examples 1, 2, and 3 each contained less than 20 ppm of lithium ions in their respective solutions, which is within the margin of error, proving that the surface layers of the three samples did not contain soluble lithium silicate. In contrast, the standard pre-lithiated sample of Comparative Example 1 contained more than 2000 ppm of lithium in its solution, indicating that without treatment, the soluble lithium silicate would dissolve in the solvent, causing hydrolysis of some of the lithium silicate and resulting in an increase in pH.

[0260] In Examples 1 to 6 of the present disclosure, pm / p Li Since this range is within the scope of the present disclosure, it is possible to further ensure high lithium ion and charge transfer ability of the material, effectively suppress the alkalinity of the material, prevent gas generation during the processing of the negative electrode material, and further improve the initial coulombic efficiency and cycle stability of the battery.

[0261] The examples described in this specification are for the purpose of interpreting the present disclosure, and the specific materials, compounding ratios, and reaction conditions described are merely specific examples and do not further limit the present disclosure, and the implementation of the present disclosure does not necessarily depend on the detailed methods described above. As those skilled in the art will understand, any technology realized based on the above content of the present disclosure falls within the scope of the present disclosure, and any improvements made to the present disclosure, equivalent substitution of each material of the product according to the present disclosure, addition of auxiliary components, selection of specific methods, etc. also fall within the protection scope and disclosure scope of the present disclosure.

[0262] Industrial Applicability

[0263] The negative electrode material according to the present disclosure can improve processability, has excellent electrochemical performance, cycle performance, and expansion suppression performance, can extend the service life of lithium-ion batteries, is simple to prepare, is low cost, is suitable for mass production, and has excellent industrial applicability. [Explanation of symbols]

[0264] 100 active materials 200 coating layer 120 Lithium Silicate 140 Water-insoluble silicates 160 Silicon-Oxygen Materials.

Claims

1. A negative electrode material, the negative electrode material includes an active material and a carbon layer formed on a surface of the active material, the active material includes a skeletal structure present throughout the active material and a silicon-oxygen material embedded in the skeletal structure, the skeletal structure includes a lithium silicate skeleton located inside the active material and a water-insoluble silicate skeleton located on a surface layer of the active material, and the water-insoluble silicate skeleton and the lithium silicate skeleton are connected to each other; In the XRD pattern of the negative electrode material, the intensity of the strongest characteristic diffraction peak of the lithium silicate is I Ａ and the intensity of the most intense characteristic diffraction peak of the water-insoluble silicate is I Ｂ and I Ｂ / I Ａ is 0.12≦I Ｂ / I Ａ Satisfies ≦0.18 A negative electrode material characterized by:

2. A negative electrode material, the negative electrode material includes an active material and a carbon layer formed on a surface of the active material; the active materials include lithium silicate, water-insoluble silicates, and silicon-oxygen materials; the water-insoluble silicate is formed so as to coat the surface of the lithium silicate; At least one of the lithium silicate and the water-insoluble silicate contains the silicon and oxygen material; In the XRD pattern of the negative electrode material, the intensity of the strongest characteristic diffraction peak of the lithium silicate is I Ａ and the intensity of the most intense characteristic diffraction peak of the water-insoluble silicate is I Ｂ and I Ｂ / I Ａ is 0.12≦I Ｂ / I Ａ Satisfies ≦0.18 A negative electrode material characterized by:

3. a. The silicon-oxygen material is SiO ｎ where n satisfies 0.5≦n≦1.5; b. The water-insoluble silicate is zA ２ O.M.O. ｙ xSiO ２ wherein M contains at least one of Mg, Al, and Ca, A contains at least one of Li, Na, and K, x satisfies 0.2≦x≦10, y satisfies 0, 1.0≦y≦3.0, and z satisfies 0≦z≦5.0, c. The water-insoluble silicate is A ２ O.nSiO ２ A contains at least one of Li, Na, and K, and n satisfies 1≦n≦10; d. the water-insoluble silicate is located within a region of the active material from a surface thereof to a depth of 20 nm to 50 nm; At least one of the conditions a to d is satisfied.

3. The negative electrode material according to claim 1 or 2.

4. a. The specific surface area of ​​the negative electrode material is 1.0 m ２ / g to 12.0m ２ / g, b) the mass content of lithium in the negative electrode material is 3 wt % to 15 wt %; c) the pH of the negative electrode material is 8.5 to 12.0; At least one of the conditions a to c is satisfied.

3. The negative electrode material according to claim 1 or 2.

5. A method for preparing the negative electrode material according to claim 1 or 2, comprising: subjecting the prelithiated carbon-coated silicon-oxygen material to a surface etching treatment; mixing the surface-etched carbon-coated silicon-oxygen material with a substance containing at least one of metal M and metal A, and carrying out a solid-state thermal reaction in a protective gas atmosphere to obtain the negative electrode material; the mass ratio of the surface-etched carbon-coated silicon / oxygen material to the substance containing at least one of metal M and metal A is 1:(0.075-0.1); The metal A-containing substance contains at least one of metal A alone, a carbonate of metal A, an oxide of metal A, and a hydroxide of metal A, and A contains at least one of Li, Na, and K; The metal M-containing substance contains at least one of the metal M simple substance, a carbonate of the metal M, an oxide of the metal M, and a hydroxide of the metal M, and M contains at least one of Mg, Al, and Ca; The temperature of the solid-phase thermal reaction is 600°C to 1200°C; the acid solution used in the surface etching treatment has a property of maintaining a pH of the surface etching reaction system below 7 when the prelithiated silicon-oxygen material is subjected to the surface etching treatment; A method for preparing a negative electrode material.

6. A method for preparing the negative electrode material according to claim 1, comprising: subjecting the prelithiated carbon-coated silicon-oxygen material to a surface etching treatment; mixing the surface-etched carbon-coated silicon-oxygen material with a compound containing metal M, and carrying out a solid-state thermal reaction under a protective gas atmosphere to obtain the negative electrode material; the mass ratio of the surface-etched carbon-coated silicon-oxygen material to the metal M-containing compound is 1:(0.075-0.1); The metal M contains at least one of Mg, Al, and Ca. The temperature of the solid-phase thermal reaction is 600°C to 1200°C; the acid solution used in the surface etching treatment has a property of maintaining a pH of the surface etching reaction system below 7 when the prelithiated silicon-oxygen material is subjected to the surface etching treatment; A method for preparing a negative electrode material.

7. The compound containing metal M is an oxide of metal M.

7. The method of claim 6.

8. a. The mixing method includes at least one of mechanical stirring and ultrasonic dispersion; b. The mixing method is ball milling, and the ball milling time is 3 hours to 24 hours; c) The time for the solid-state thermal reaction is 3 hours to 12 hours; d. The temperature rise rate of the solid-phase thermal reaction is 1°C / min to 5°C / min; At least one of the conditions a to d is satisfied.

6. The method of claim 5.

9. a. the prelithiated carbon-coated silicon and oxygen material is obtained by reacting a carbon-coated silicon and oxygen material with a lithium source; b. The silicon-oxygen material is SiO ｎ where n satisfies 0.5≦n≦1.5; c. The average particle size (D50) of the silicon and oxygen material is 2.0 μm to 15.0 μm; d) The lithium source includes at least one of lithium elemental element and lithium-containing compound; e. The reaction temperature between the carbon-coated silicon-oxygen material and the lithium source is 150°C to 300°C; f. The reaction time between the carbon-coated silicon-oxygen material and the lithium source is 2.0 hours to 6.0 hours; g. The mass ratio of the carbon-coated silicon-oxygen material to the lithium source is 1:(0.01-0.20); h. The mass content of lithium in the prelithiated carbon-coated silicon-oxygen material is 3 wt % to 20 wt %; At least one of the conditions a to h is satisfied.

6. The method of claim 5.

10. and reacting the carbon-coated silicon and oxygen material with a lithium source to obtain a prelithiated carbon-coated silicon and oxygen material prior to the step of subjecting the prelithiated carbon-coated silicon and oxygen material to a surface etching treatment.

6. The method of claim 5.

11. a. The acid solution used in the surface etching treatment contains at least one of hydrochloric acid, acetic acid, nitric acid, citric acid, oxalic acid, sulfuric acid, formic acid, phenol, phosphoric acid, hydrogen phosphate, hydroiodic acid, hydrobromic acid, ethylenediaminetetraacetic acid, glycolic acid, gluconic acid, and succinic acid; b. The surface etching treatment time is 0.5 hours to 10.0 hours; At least one of the conditions a to b is satisfied.

6. The method of claim 5.

12. The negative electrode material according to claim 1 or 2 is included. A lithium-ion battery characterized by:

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