Negative electrode material, method for preparing the same, and secondary battery

Abstract

The application provides a negative electrode material and a preparation method thereof and a secondary battery, and relates to the technical field of battery materials. The negative electrode material comprises a silicon-based inner core and a carbon layer coated on the surface of the silicon-based inner core, wherein the silicon-based inner core comprises nanosilicon and a silicate containing a metal element M; the negative electrode material is subjected to section analysis and energy spectrum analysis, and meets the conditions of k1<=10, k2<=5 and 0.1 The preparation method of the negative electrode material comprises the following steps: heating and evaporating pre-disproportionated silicon monoxide material and M metal source material to obtain silicon monoxide gas and metal source gas; mixing and condensing the two kinds of gas to obtain an inner core material; and performing carbon coating treatment to obtain the negative electrode material. In the negative electrode material prepared by the application, the metal silicate effectively separates the nanosilicon domain and the silicon oxide domain, and is uniformly distributed, and the negative electrode material has high initial efficiency and excellent cycle performance.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of battery materials, in particular to a negative electrode material, a preparation method thereof and a secondary battery. BACKGROUND

[0002] Among a large number of negative electrode materials, silicon oxide negative electrode material is a high specific capacity negative electrode material with relatively mature application technology. Compared with graphite negative electrode material, the specific capacity of silicon oxide negative electrode material is as high as 2100 mAh / g; compared with crystal silicon negative electrode material, the silicon oxide negative electrode material overcomes the problem of large volume expansion, greatly improving the cycle life of the negative electrode material. However, due to the formation process of Li2O and lithium silicate in the first lithium intercalation process of the silicon oxide material being irreversible, the lithium loss caused by these irreversible reactions leads to a low first coulombic efficiency, and in the design of a secondary battery, an excessive positive electrode capacity is required to match. This not only offsets the high specific capacity of the negative electrode, but also reduces the energy density of the secondary battery; on the other hand, it also increases the positive electrode consumption cost of the secondary battery.

[0003] To solve the problem of low initial charge-discharge coulombic efficiency, the oxygen content in the silicon oxide can be reduced in advance to reduce the consumption of lithium ions in the positive electrode material caused by the irreversible phase Li2O generated during the first charging, thereby improving the energy density of the secondary battery. Common methods include adding exogenous reducing metal elements to react with oxygen elements in the silicon oxide to reduce nanosilicon, thereby improving the coulombic efficiency of the material, and the metal oxide or silicate generated by the reduction reaction can act as a buffer matrix to adjust the stress damage caused by the volume change of nanosilicon during lithium alloying and dealloying, thereby maintaining the structural integrity and improving the long-term cycle performance of the material.

[0004] For example, a method for improving the first-week coulombic efficiency of silicon oxide by mixing silicon monoxide powder with magnesium powder and heating for solid-phase doping reduction reaction. The negative electrode material prepared by the method has stable physical and chemical properties of magnesium silicate, and good stability of water-based slurry. However, the magnesium thermal reduction reaction is a diffusion-controlled reaction, and the composition of the product is closely related to the diffusion rate of magnesium vapor. When the powder is mixed in a micron level, the generated magnesium vapor reacts from the outside of the silicon monoxide particles and gradually diffuses to the inside of the particles, which easily leads to the generation of magnesium silicide, magnesium oxide and rapid growth of silicon grains due to local excess of magnesium. Moreover, since the diffusion rate of magnesium vapor into the solid is generally small, it is difficult for magnesium to be completely and uniformly doped into the inside of the silicon monoxide material, and the distribution of magnesium in the reduction product is also relatively uneven.

[0005] For the in-situ gaseous magnesium doping technology, a method of mixing silicon and silicon dioxide mixture with metal M and then performing vacuum co-evaporation condensation is also disclosed. The first efficiency of the negative electrode material prepared by the method is above 83%, which greatly improves the effective utilization rate of lithium ions in the secondary battery positive electrode material, and the water-based slurry has good stability. However, since the reaction of the silicon and silicon dioxide mixture used in the method to generate silicon oxide vapor under heating conditions is a solid-solid interface reaction, the amount of generated silicon oxide vapor will fluctuate greatly as the reaction proceeds. Therefore, the local magnesium doping ratio is uncontrollable during the mixing and deposition of magnesium vapor and silicon oxide vapor, which easily leads to uneven growth of silicon grains and affects the cycle life and safety of the negative electrode material.

[0006] Obviously, whether it is a solid-phase doping or an in-situ gaseous doping technology, the distribution of the doping elements in the prepared negative electrode material is uneven, or the growth of silicon grains is uneven, that is, it is difficult to simultaneously satisfy the uniform distribution of the doping elements between single particles and multiple particles. Therefore, there is an urgent need to prepare a new negative electrode material to improve its electrochemical performance. SUMMARY

[0007] The purpose of the present application is to provide a negative electrode material, a preparation method thereof and a secondary battery. Through an in-situ doping technology, the doping of nanoscale metal M is realized, the negative electrode material with uniform distribution of metal M is obtained, the oxygen content in the negative electrode material is reduced, and the first efficiency and cycle performance are improved when the material is applied in a battery.

[0008] To achieve the above purpose, the technical solutions of the present application are as follows:

[0009] In a first aspect, the present application provides a negative electrode material, comprising a silicon-based inner core and a carbon layer coated on the surface of the silicon-based inner core, wherein the silicon-based inner core comprises nanosilicon and a silicate containing metal M element.

[0010] The negative electrode material is subjected to section analysis and energy spectrum analysis, a section of n1 particles is randomly selected for surface scanning analysis to obtain n1 M element content values, the standard deviation k1 of the n1 M element content values is calculated, and k1≤10; n2 points are randomly selected inside the section of the particles for point scanning analysis to obtain n2 M element content values, the standard deviation k2 of the n2 M element content values is calculated, and k2≤5, and 0.1

[0011] In combination with the first aspect, in a preferred embodiment of the present application, the negative electrode material satisfies at least one of the following conditions:

[0012] (1) The silicon-based inner core further comprises silicon oxide;

[0013] (2) the pH value of the negative electrode material satisfies 7 < pH≤10.5;

[0014] (3) the M element comprises at least one metal element in IA, IIA and IIIA groups;

[0015] (4) the M element comprises at least one of lithium, sodium, potassium, magnesium, calcium and aluminum;

[0016] (5) the true density of the negative electrode material is 2.0 g / cm 3 -2.6 g / cm 3 ;

[0017] (6) the specific surface area of the negative electrode material is 2 m 2 / g-10 m 2 / g;

[0018] (7) in the negative electrode material, the mass percentage of the M element is 3%-20%, and the mass percentage of the carbon layer is 1%-20%;

[0019] (8) when the metal M element-containing silicate comprises MgSiO3, in the XRD spectrum of the negative electrode material, the diffraction peak of MgSiO3(610) is between 30° and 31°, the diffraction peak of Si(220) is between 45° and 50°, and the ratio of the intensity of the two diffraction peaks α = I Si(220) / I MgSiO3(610) , 0 < α < 2;

[0020] (9) when the metal M element-containing silicate comprises MgSiO3, according to the XRD spectrum of the negative electrode material and the Scherrer formula Kλ = 0.9λ / Bcosθ, the average size of MgSiO3 grains on the (610) crystal face is calculated to be ≤30 nm.

[0021] Further preferably, the negative electrode material further satisfies at least one of the following conditions:

[0022] (10) the nanosilicon is dispersed in the silicon oxide;

[0023] (11) the nanosilicon or the silicon oxide is wrapped by the metal M element-containing silicate.

[0024] In combination with the first aspect, in a preferred embodiment of the present application, the thickness of the carbon layer is 50 nm-500 nm.

[0025] Secondly, the present application further provides a preparation method of the negative electrode material of the first aspect, comprising:

[0026] The metal source material and the pre-disproportionated silicon monoxide material are placed in different positions of the same vacuum heating system and heated and evaporated respectively to obtain metal source gas and silicon monoxide gas;

[0027] The silicon monoxide gas and the metal source gas are mixed and condensed to obtain the core material;

[0028] The core material is subjected to carbon coating treatment to obtain the negative electrode material.

[0029] In combination with the second aspect, in a preferred embodiment of the present application, the preparation method satisfies at least one of the following conditions:

[0030] A. The preparation method of the pre-disproportionated silicon monoxide material comprises: pre-disproportionating an amorphous SiO bulk to obtain silicon monoxide containing silicon grains <20 nm, and then performing powderization or crushing treatment to obtain the pre-disproportionated silicon monoxide powder or particles;

[0031] B. The size of the pre-disproportionated silicon monoxide material is ≤10 cm;

[0032] C. The metal source material comprises at least one of magnesium source material, lithium source material, sodium source material, potassium source material, calcium source material, and aluminum source material;

[0033] D. The metal source gas comprises at least one of magnesium vapor, lithium vapor, sodium vapor, potassium vapor, calcium vapor, and aluminum vapor;

[0034] E. The heating and evaporation is performed in a vacuum or an atmosphere of inert gas;

[0035] F. The temperature for heating and evaporation of the pre-disproportionated silicon monoxide material is 1000-1500°C;

[0036] G. The temperature for heating and evaporation of the metal source material is 600-1350°C;

[0037] H. The condensation temperature is 500-800°C;

[0038] I. The condensation mode comprises at least one of water cooling and air cooling;

[0039] J. After the condensation, the method further comprises: collecting the precursor material after the condensation, and performing crushing and grading treatment on the precursor material to obtain the core material;

[0040] K. The carbon coating treatment comprises gas phase coating, liquid phase coating, or solid phase coating.

[0041] Further preferably, the preparation method further satisfies at least one of the following conditions:

[0042] L. the pre-decomposition treatment is performed in an inert gas atmosphere, the inert gas comprising at least one of nitrogen, argon, and helium;

[0043] M. the pre-decomposition treatment is performed at a temperature of 1000-1200℃;

[0044] N. the pre-decomposition treatment is performed for a holding time of 3-10h;

[0045] O. the magnesium source material comprises at least one of metallic magnesium powder, metallic magnesium ingot, metallic magnesium particle, a mixture of magnesium-containing oxide and reducing substance, and a mixture of magnesium-containing salt and reducing substance.

[0046] P. the pulverization is performed by at least one of mechanical pulverization, ball milling, and air flow pulverization;

[0047] Q. the gas for the gas phase coating comprises a carbon source gas and a carrier gas;

[0048] R. the gas phase coating is performed at a temperature of 700-1000℃.

[0049] Further, the preparation method satisfies at least one of the following conditions:

[0050] S. the carbon source gas comprises at least one of methane, ethane, propane, butane, ethylene, propylene, and acetylene;

[0051] T. the carrier gas comprises at least one of nitrogen, argon, and helium;

[0052] U. the gas for the gas phase coating further comprises hydrogen.

[0053] In combination with the second aspect, in a preferred embodiment of the present application, the silicon monoxide gas and the metal source gas are mixed under vacuum conditions at a vacuum degree of 0-100Pa.

[0054] In a third aspect, the present application further provides a secondary battery comprising the negative electrode material of the first aspect or the negative electrode material prepared by the preparation method of the second aspect.

[0055] The present application has the following advantages:

[0056] The metal element M-containing silicate in the negative electrode material system of the present application can obtain the distribution of the M element in accordance with certain characteristics through energy spectrum analysis, and the metal element M-containing silicate can effectively separate the nano-silicon domain and the silicon oxide domain, reduce the performance degradation problem of the negative electrode material caused by the aggregation of silicon clusters due to the electrochemical sintering of nano-silicon in the charging and discharging cycle process, so that the negative electrode material has high initial efficiency and excellent cycle performance, and the silicate can act as a buffer matrix of nano-silicon and silicon oxide to buffer the volume change caused by lithium intercalation and deintercalation in the process of lithium intercalation and deintercalation, so that the negative electrode material has low expansion performance.

[0057] Further, the pH of the negative electrode material of the present application is in the range of 7 - , the gas production problem between the active silicon and OH - in the alkaline solution during the preparation of the negative electrode material slurry, the bubble problem of the electrode sheet coating, and the cycle performance degradation problem caused by the performance degradation of the alkaline binder, etc. When the metal element M-containing silicate is mainly MgSiO3, the H2SiO3 generated by the hydrolysis of MgSiO3 results in relatively weak alkalinity of the slurry, and when the content of MgSiO3 is relatively low and the content of Mg2SiO4 is relatively high, a large amount of Mg2SiO4 will hydrolyze to generate H4SiO4, and more OH - will be generated, which will cause the alkalinity of the slurry to become stronger, and OH - will react with the exposed active silicon in the negative electrode material to generate H2, thereby affecting the safety performance of the battery.

[0058] The preparation method of the negative electrode material of the present application is simple and easy to operate, and can realize rapid industrialization. Through in-situ doping technology, the mixed deposition of gaseous metal source and gaseous silicon oxide is realized, the nanoscale doping of metal is realized, and the negative electrode material with uniform distribution of metal silicate is obtained. Especially, pre-isomerized silicon monoxide material is used in the preparation method, which can continuously and stably generate silicon monoxide vapor, and then mixed with the stably generated metal source gas to obtain a negative electrode material with uniform distribution of each substance and better performance, thereby reducing the problem of uneven doping of each substance in the prepared negative electrode material caused by unstable evaporation of silicon monoxide due to the influence of material contact effect on the interface reaction when using a mixture of traditional silicon and silicon dioxide as raw material.

[0059] The secondary battery of the present application uses the above-mentioned negative electrode material, which has higher initial efficiency and excellent charging and discharging cycle performance. BRIEF DESCRIPTION OF DRAWINGS

[0060] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following will briefly introduce the drawings needed to be used in the embodiments. It should be understood that the following drawings only show some embodiments of the present application, and therefore should not be regarded as a limitation on the scope of the present application.

[0061] Figure 1 XRD pattern of the negative electrode material prepared for Example 1;

[0062] Figure 2 SEM / EDS surface mapping of a certain particle section of the negative electrode material prepared for Example 1;

[0063] Figure 3 High magnification SEM image of a certain particle section of the negative electrode material prepared for Example 1;

[0064] Figure 4 Cycle capacity performance graph of the secondary batteries prepared for Example 1 and Comparative Example 1;

[0065] Figure 5 Cycle expansion performance graph of the secondary batteries prepared for Example 1 and Comparative Example 1. DETAILED DESCRIPTION

[0066] As used herein the terms "have," "has," "have," "having," or the like, are used to describe

[0067] "comprise," "comprising," "containing," "contain," "including," "including," "includes," "include," or any other variation thereof, are intended to cover a non-exclusive inclusion. For example, a composition, process, method, article, or apparatus that "comprises," "comprising," "containing," "contain," "including," "including," "includes," "include," or the like, a list of elements is not limited to those elements but can include other elements not expressly listed or inherent to such composition, process, method, article, or apparatus. The term "consisting of" excludes any element, step, or component not specified.

[0068] When expressing a value, concentration, or other value or parameter of a range, preferably a range, or a series of upper preferred values and lower preferred values, it should be understood that all ranges formed by any pair of an upper range limit or preferred value and a lower range limit or preferred value, regardless of whether the range is expressly disclosed, are specifically disclosed. For example, when a range "1-5" is disclosed, the described range should be interpreted as including the range "1-4", "1-3", "1-2", "1-2 and 4-5", "1-3 and 5", etc. When numerical ranges are described herein, unless otherwise stated, the range is intended to include its end values and all integers and fractions within the range.

[0069] In these examples, the parts and percentages described are by mass, unless otherwise indicated.

[0070] "Parts by mass" refers to a basic unit of measurement indicating the mass ratio relationship of multiple components, 1 part can represent an arbitrary unit of mass, such as 1 g, or 2.689 g, etc. If we say that the mass of component A is a parts, and the mass of component B is b parts, it means that the ratio of the mass of component A to the mass of component B is a:b. Alternatively, it means that the mass of component A is aK, and the mass of component B is bK (K is an arbitrary number, indicating a multiple factor). It should not be misunderstood that, unlike parts by mass, the sum of the parts by mass of all components is not limited to 100 parts.

[0071] "and / or" is used to indicate that one or both of the described cases can occur, for example, A and / or B includes (A and B) and (A or B).

[0072] In order to obtain a silicon-oxygen negative electrode material with excellent performance, in the research of the prior art, a silicon-based composite negative electrode material is prepared by uniformly doping gaseous lithium generated by the redox reaction of lithium-containing oxide or silicate with a reducing agent into silicon powder and silicon micro powder, and the initial efficiency can be as high as about 90%, but the negative electrode material prepared has large silicon crystal grains and poor cycle performance. There are also silicon powder, SiO2 powder, magnesium powder and LiCl powder in the same vacuum system, heated and sublimated, and a magnesium-lithium co-doped modified precursor is obtained after cooling, and then a conductive layer is coated to obtain a negative electrode material which not only has high initial efficiency, but also has the characteristics of high ionic conductivity of lithium silicate and high bond strength of magnesium silicate, further improving the cycle life of the material, but the preparation conditions are harsh, and the expansion of the negative electrode material during charging and discharging is too large. At the same time, a silicon-based negative electrode material is prepared by mixing silicon, silicon dioxide mixture and metal M and using vacuum co-evaporation condensation method, although the initial efficiency of the material is improved, but because the evaporation mixing uniformity is poor, the size of the silicon crystal grains produced is uneven, the electrical performance is poor, and there is a certain safety risk.

[0073] The most important purpose of the present application is to solve the problem of mixing two-phase and multi-phase steam, prepare a negative electrode material with metal M element meeting certain distribution characteristics, and further make the negative electrode material have high initial efficiency and excellent cycle performance, and also have low expansion performance.

[0074] In a first aspect, the present application provides a negative electrode material, which comprises a silicon-based inner core and a carbon layer coated on the surface of the silicon-based inner core. The silicon-based inner core of the negative electrode material comprises nanosilicon and silicate containing metal M element.

[0075] Among them, the section and energy spectrum analysis of the negative electrode material are carried out, especially the distribution of M element in the inner core is analyzed, and the k1 value and k2 value are obtained by calculating the results.

[0076] Specifically, n1 particles of the negative electrode material are randomly selected for sectioning, surface scanning energy spectrum analysis is performed on the sections of the n1 particles to obtain n1 M element content values, the standard deviation k1 of the n1 metal M element content values is calculated, and k1≤10. In the interior of the section of the particle, n2 points are randomly selected for point scanning analysis to obtain n2 M element content values, the standard deviation k2 of the n2 M element content values is calculated, k2≤5, and the k1 value and the k2 value further satisfy 0.1

[0077] The negative electrode material satisfying the condition can effectively separate the nanosilicon domains and the silicon oxide domains in the metal silicate in the silicon-based core, and reduce the performance degradation problem of the negative electrode material caused by the aggregation of silicon clusters.

[0078] In a preferred embodiment of the present application, the pH value of the negative electrode material of the present application satisfies 7

[0079] It can be understood that if the pH value in the negative electrode material is too high, when the negative electrode material is prepared into a negative electrode slurry, the exposed Si will react with OH - in the slurry to produce H2, which will cause problems such as bubble coating of the slurry, performance degradation of the alkaline binder, and further cause cycle performance degradation, battery capacity initial effect attenuation, battery use safety and other problems. The pH value of the negative electrode material of the present application is not more than 10.5, which greatly reduces the generation of gas and improves the performance of the battery.

[0080] The metal M element-containing silicate can be written as (MO) n ·SiO2, so when the pH of the negative electrode material meets the above range, (MO) n The silicate with low proportion of (MO) - and high proportion of SiO2 will be the main silicate phase in the negative electrode material. Taking the metal magnesium silicate as an example, when MgSiO3 (MgO·SiO2) is the main silicate phase in the negative electrode material, the pH value of the negative electrode material will be relatively low, however, if the content of Mg2SiO4 (2MgO·SiO2) is relatively high, Mg2SiO4 will hydrolyze to produce more OH -react with exposed active Si to generate H2, which leads to the capacity fade of the initial capacity and the gas generation during the slurry coating process, which may cause the battery to swell and even burst, leading to safety risks. Therefore, when 0 < m(Mg2SiO4) / m(MgSiO3) ≤ 1, the ability to increase the pH value is weak; thus, the pH value of the negative electrode material can be stably maintained in the range of 7 < pH ≤ 10.5, which reduces the problem of the exposed Si in the negative electrode material reacting with OH - reacting with exposed active Si to generate H2, which leads to the capacity fade of the initial capacity and the gas generation during the slurry coating process, which may cause the battery to swell and even burst, leading to safety risks. Therefore, when 0 < m(Mg2SiO4) / m(MgSiO3) ≤ 1, the ability to increase the pH value is weak; thus, the pH value of the negative electrode material can be stably maintained in the range of 7 < pH ≤ 10.5, which reduces the problem of the exposed Si in the negative electrode material reacting with OH

[0081] When the negative electrode material simultaneously satisfies the ranges of k1 and k2 and the range of the pH value, the silicate containing the metal M element is uniformly distributed in the core, and the nanosilicon or silicon oxide is encapsulated and isolated, reducing the problems of the gas generation during the slurry coating process and the sintering of the nanosilicon clusters during the cycle process caused by the exposure of the active silicon, thereby bringing a more stable material structure and reducing the consumption of the active silicon during the cycle process.

[0082] In a preferred embodiment of the present application, the silicon-based core of the negative electrode material further includes silicon oxide. More preferably, the nanosilicon is dispersed in the silicon oxide, and the nanosilicon or the silicon oxide is encapsulated by the silicate containing the metal M element. Through the multiple protection of the silicon oxide and the metal silicate, the exposure of the active silicon can be further reduced, and the volume expansion rate during the charge and discharge process is also reduced.

[0083] The silicon oxide can be expressed by the general formula SiO x (0.5 ≤ x ≤ 2). It can be a material formed by dispersing silicon particles in SiO2, or a material having a tetrahedral structural unit, in which a silicon atom is located at the center of the tetrahedral structural unit, and a silicon atom and an oxygen atom are located at four vertices of the tetrahedral structural unit.

[0084] In a preferred embodiment of the present application, the metal M element includes at least one metal element in the IA, IIA, and IIIA groups.

[0085] In a preferred embodiment of the present application, the M element includes at least one of lithium, sodium, potassium, magnesium, calcium, and aluminum, and more preferably, the M element is a magnesium element.

[0086] In a preferred embodiment of the present application, the true density of the negative electrode material is 2.0 g / cm 3 -2.6 g / cm 3 , for example, can be 2.0 g / cm 3 , 2.1 g / cm 3 , 2.2 g / cm 3 , 2.3 g / cm 32.4 g / cm3 3 2.5 g / cm3 3 or 2.6 g / cm3 3 More preferably, the true density is 2.3 g / cm3 3 -2.6 g / cm3 3 .

[0087] The true density of the negative electrode material of the present application is tested by the gas adsorption expansion method.

[0088] In a preferred embodiment of the present application, the specific surface area of the negative electrode material is 2 m 2 / g-10 m 2 / g, for example, it can be 2 m 2 / g, 4 m 2 / g, 6 m 2 / g, 8 m 2 / g or 10 m 2 / g.

[0089] In a preferred embodiment of the present application, the mass percentage of the M element in the negative electrode material is 3%-20%, for example, it can be 3%, 5%, 7%, 10%, 12%, 15%, 18% or 20%.

[0090] In a preferred embodiment of the present application, the mass percentage of the surface carbon layer of the negative electrode material is 1%-20%, for example, it can be 1%, 3%, 5%, 8%, 10%, 12%, 15%, 18% or 20%, more preferably 3%-7%.

[0091] In a preferred embodiment of the present application, the thickness of the surface carbon layer is 50 nm-500 nm, for example, it can be 50 nm, 100 nm, 200 nm, 300 nm, 400 nm or 500 nm.

[0092] In a preferred embodiment of the present application, when the silicate containing the metal M element includes MgSiO3, in the XRD spectrum of the negative electrode material, the diffraction peak of MgSiO3(610) is between 30°-31°, the diffraction peak of Si(220) is between 45°-50°, and the ratio of the intensity of the two diffraction peaks α = I Si(220) / I MgSiO3(610) , 0 < α < 2.

[0093] In a preferred embodiment of the present application, when the silicate containing the metal M element includes MgSiO3, according to the XRD spectrum of the negative electrode material and the Scherrer formula Kλ = 0.9λ / Bcosθ, the average size of the MgSiO3 crystal grains on the (610) crystal face is ≤30 nm.

[0094] In a second aspect, the application also provides a preparation method of the negative electrode material in the first aspect, comprising:

[0095] S1, placing a metal source material and a pre-disproportionated silicon monoxide material in different positions of a same vacuum heating system to be heated and evaporated respectively to obtain a metal source gas and a silicon monoxide gas;

[0096] S2, mixing and condensing the silicon monoxide gas and the metal source gas to obtain a core material;

[0097] S3, performing carbon coating treatment on the core material to obtain the negative electrode material.

[0098] In combination with the second aspect, in a preferred embodiment of the application, the preparation method of the pre-disproportionated silicon monoxide material in S1 comprises: performing pre-disproportionation treatment on an amorphous SiO bulk to obtain silicon monoxide containing silicon grains <20 nm, and then performing powderization or crushing treatment to obtain a pre-disproportionated silicon monoxide powder or particle.

[0099] Further preferably, the pre-disproportionation treatment is performed in an atmosphere of an inert gas, which comprises at least one of nitrogen, argon and helium.

[0100] Further preferably, the temperature of the pre-disproportionation treatment is 1000-1200℃, for example, it can be 1000℃, 1050℃, 1100℃, 1150℃ or 1200℃, and the holding time is 3-10h, for example, it can be 3h, 5h, 6h, 8h or 10h. More preferably, the pre-disproportionation treatment is performed at 1000℃ for 10h.

[0101] It should be noted that the pre-disproportionated silicon monoxide material is selected as the silicon monoxide source in the application, mainly to reduce the instability of SiO evaporation caused by the influence of material contact effect on the interface reaction when traditional silicon and silicon dioxide are selected as raw materials. Among them, the amorphous SiO is subjected to homogenization disproportionation treatment to obtain silicon monoxide containing silicon grains <20 nm, which realizes the micro-nano uniform dispersion of Si and SiO2 in the silicon monoxide vapor source, stabilizes the generation rate of the silicon monoxide vapor in the whole reaction process, and realizes the relatively uniform generation, mixing and condensation deposition of the silicon monoxide gas and the metal M source gas.

[0102] In a preferred embodiment of the application, the size of the pre-disproportionated silicon monoxide material in S1 is ≤10cm, for example, it can be 10μm, 100μm, 1mm, 1cm, 5cm or 10cm.

[0103] In a preferred embodiment of the present application, the metal source material in S1 comprises at least one of a magnesium source material, a lithium source material, a sodium source material, a potassium source material, a calcium source material, and an aluminum source material, and more preferably a magnesium source material.

[0104] Further preferably, the magnesium source material comprises at least one of a magnesium metal powder, a magnesium metal ingot, a magnesium metal particle, a mixture of a magnesium-containing oxide and a reducing substance, and a mixture of a magnesium-containing salt and a reducing substance.

[0105] In a preferred embodiment of the present application, the metal source gas in S1 comprises at least one of magnesium vapor, lithium vapor, sodium vapor, potassium vapor, calcium vapor, and aluminum vapor, and more preferably magnesium vapor.

[0106] In a preferred embodiment of the present application, when the metal source material and the pre-deformed silicon monoxide material are heated and evaporated at different positions of the same vacuum heating system, the pre-deformed silicon monoxide material can be heated and evaporated in a first vacuum heating chamber to obtain a silicon monoxide gas; and the metal source material can be heated and evaporated in a second vacuum heating chamber to obtain a metal source gas.

[0107] Specifically, the first vacuum heating chamber is supplied with an inert gas, and the temperature is heated to 1000-1500°C to obtain a silicon monoxide gas, for example, 1000°C, 1100°C, 1200°C, 1300°C, 1400°C, or 1500°C.

[0108] The second vacuum heating chamber is supplied with an inert gas, and the temperature is heated to 700-1300°C to obtain a metal source gas, for example, 700°C, 800°C, 900°C, 1000°C, 1100°C, or 1200°C.

[0109] It can be understood that the heating and evaporation temperatures of the metal source material and the pre-deformed silicon monoxide material in the same vacuum heating system can be the same or different.

[0110] In a preferred embodiment of the present application, the mixing of the two gases in S2 is performed under vacuum conditions with a vacuum degree of 0-100 Pa.

[0111] In a preferred embodiment of the present application, the condensation temperature in S2 is 500-900°C, for example, 500°C, 600°C, 700°C, 800°C, or 900°C.

[0112] Further preferably, the condensation method comprises at least one of water cooling and air cooling.

[0113] Specifically, the condensation deposition chamber is vacuumized, and when the vacuum degree reaches 100 Pa or less and the temperature of the condensation chamber reaches 500-900 ℃, the gases in the two vacuum heating chambers are mixed and introduced into the condensation deposition chamber, and then the precursor mixed with the silicon oxide and the metal source is collected on the condenser.

[0114] In a preferred embodiment of the present application, after condensation in S2, the method further comprises collecting the condensed precursor material, and then crushing and grading the precursor material to obtain the core material.

[0115] Further preferably, the crushing method comprises any one of mechanical crushing, ball milling, and airflow crushing.

[0116] In a preferred embodiment of the present application, the carbon coating treatment in S3 comprises gas phase coating, liquid phase coating, or solid phase coating.

[0117] When the surface carbon layer is prepared using gas phase coating, the gas required for the gas phase coating comprises a carbon source gas and a carrier gas; the temperature for the gas phase coating is 700-1000 ℃, for example, it can be 700 ℃, 800 ℃, 900 ℃, or 1000 ℃.

[0118] Optionally, the carbon source gas comprises at least one of methane, ethane, propane, butane, ethylene, propylene, and acetylene.

[0119] Optionally, the carrier gas comprises at least one of nitrogen, argon, and helium.

[0120] Further preferably, in the gas phase coating process, in addition to the carbon source gas and the carrier gas, a certain proportion of hydrogen can also be introduced, which is mainly used for adjusting the structure of the carbon layer.

[0121] In a third aspect, the present application also provides a secondary battery comprising the negative electrode material of the first aspect or the negative electrode material prepared by the preparation method of the second aspect.

[0122] More preferably, the secondary battery is a non-aqueous electrolyte rechargeable battery.

[0123] By using the in-situ doping technology, the gaseous magnesium is used as the magnesium source to mix and deposit with the gaseous silicon oxide to realize the nanoscale magnesium doping, and the negative electrode material meeting the distribution characteristics and pH range of the metal M is obtained, and then the active material is reduced by heat treatment to reduce the oxygen content, and then the high initial efficiency silicon monoxide negative electrode material is obtained through powderization and carbon coating.

[0124] In the preparation method of the negative electrode material of the present application, by using the silicon monoxide source, pre-isomerization treatment is performed, and the Si and SiO xIn any place, it is uniformly dispersed in nanoscale, the silicon crystal grain is less than 20 nm, the influence of the change of the reaction rate caused by the change of the interface reaction contact area is reduced, the silicon monoxide vapor can be continuously and stably generated, after the magnesium vapor is continuously and stably generated, the high initial efficiency silicon oxide negative electrode product with uniform distribution and better performance is obtained.

[0125] The embodiments of the present application will be described in detail below with specific examples, but those skilled in the art will understand that the following examples are only for illustration of the present application and should not be regarded as limiting the scope of the present application. If the specific conditions are not specified in the examples, the conventional conditions or the conditions recommended by the manufacturer are used. If the manufacturer of the reagent or instrument is not specified, it is a conventional product that can be obtained by market purchase.

[0126] Example 1

[0127] The present application provides a negative electrode material, and a preparation method thereof comprises:

[0128] 1) The amorphous SiO bulk is pre-isomerization treated at 1200℃ in an argon gas atmosphere for 10h, and after cooling, powder treatment is performed to obtain a pre-isomerization silicon monoxide powder containing silicon crystal grains with an average size of 6.0nm, the volume distribution D50 of the powder is 100μm, then the powder is placed in a first vacuum heating chamber of a vacuum heating system, argon is introduced, and heated to 1400℃ to obtain a silicon monoxide gas;

[0129] 2) The metal magnesium powder is placed in a second vacuum heating chamber of the vacuum heating system, argon is introduced, and heated to 700℃ to obtain a magnesium vapor;

[0130] 3) The vacuum heating system is vacuumed to a vacuum degree of 10Pa;

[0131] 4) The gas obtained from the first vacuum heating chamber and the gas from the second vacuum heating chamber are introduced into a condensation deposition chamber with a vacuum degree of 10Pa, and the precursor material is collected on a water-cooled substrate with a condensation deposition chamber temperature of 700℃;

[0132] 5) The precursor of step 4) is crushed to a volume distribution D50 of 5.5μm by mechanical crushing, classification and other means;

[0133] 6) The powder material obtained in step 5) is placed in a rotary furnace, heated to 900℃, and introduced into methane, hydrogen and carrier gas nitrogen, the atmosphere ratio is adjusted to 2:1:3.5, and the gas phase coating is 8h;

[0134] 7) The coated material is collected, dispersed and sieved to remove the magnet, and a silicon oxide-containing composite negative electrode material is obtained.

[0135] The present application provides a secondary battery, and the specific preparation method comprises:

[0136] The negative electrode material, conductive carbon black, and PAA glue prepared in the above example were mixed in a mass ratio of 75:15:10 to prepare a negative electrode slurry, which was coated on a copper foil, dried, and then formed into a negative electrode sheet. A lithium metal sheet was used as a counter electrode to assemble a button cell in an argon-filled glove box.

[0137] The button cell was subjected to charge-discharge tests at a current density of 0.1 C and in a charge-discharge interval of 0.01-1.5 V. The first reversible specific capacity and the first efficiency of the battery were obtained by the tests.

[0138] The embodiment also provides a secondary battery, and the specific preparation method comprises the following steps:

[0139] The negative electrode material prepared in the above example, Super-P, KS-6, CMC, and SBR were mixed in a mass ratio of 92:2:2:2:2 to prepare a negative electrode slurry, which was coated on a copper foil, dried, and then formed into a negative electrode sheet. A lithium metal sheet was used as a counter electrode to assemble a button cell in an argon-filled glove box.

[0140] The button cell was subjected to charge-discharge tests at a current density of 1 C and in a charge-discharge interval of 0.01-1.5 V. The volume expansion rate and the capacity retention rate of the battery after 50 cycles were obtained by the tests, and the expansion performance in the cycle process was studied by a prismatic soft-pack battery in-situ expansion rate test method.

[0141] Embodiment 2

[0142] The embodiment provides a negative electrode material, and the preparation method comprises the following steps:

[0143] 1) The amorphous SiO bulk was subjected to a pre-deformation treatment in an argon gas atmosphere at 1200℃ for 10 h, and then was subjected to a powder treatment after cooling to obtain a pre-deformation silicon monoxide powder containing silicon grains with an average size of 6.0 nm. The volume distribution D50 of the powder was 100 μm. Then, the powder was placed in a first vacuum heating chamber of a vacuum heating system, argon was introduced, and the temperature was heated to 1300℃ to obtain a silicon monoxide gas;

[0144] 2) The metal magnesium powder was placed in a second vacuum heating chamber of the vacuum heating system, argon was introduced, and the temperature was heated to 900℃ to obtain a magnesium vapor;

[0145] 3) The vacuum heating system was vacuumized to a vacuum degree of 5 Pa;

[0146] 4) The gas obtained from the first vacuum heating chamber and the gas from the second vacuum heating chamber were introduced into a condensation deposition chamber with a vacuum degree of 5 Pa, and a precursor material was collected on a water-cooled substrate with a condensation deposition chamber temperature of 800℃;

[0147] 5) The precursor of step 4) is crushed to a volume distribution D50 = 5.0 μm by mechanical crushing, classification and other means;

[0148] 6) The powder material obtained in step 5) is placed in a rotary furnace, heated to 980°C, and a gas atmosphere of methane, hydrogen and carrier gas argon is introduced, with the atmosphere ratio adjusted to 3:1:3.5, and gas phase coating for 10 h;

[0149] 7) The coated material is collected, dispersed, screened and de-magnetized to obtain a silicon oxide-containing composite negative electrode material.

[0150] The production and evaluation of the secondary battery provided in this example are the same as in Example 1.

[0151] Example 3

[0152] This example provides a negative electrode material, and the preparation method thereof is the same as in Example 1, except that:

[0153] In step 2), the calcium metal powder is placed in the second vacuum heating chamber of the vacuum heating system, argon is introduced, and heated to 1300°C.

[0154] The production and evaluation of the secondary battery provided in this example are the same as in Example 1.

[0155] Example 4

[0156] This example provides a negative electrode material, and the preparation method thereof is the same as in Example 1, except that:

[0157] In step 1), the temperature for pre-deformation treatment is 1000°C, and the time is 10 h, to obtain a pre-deformation silicon monoxide powder with a silicon grain size of 5.5 nm.

[0158] The production and evaluation of the secondary battery provided in this example are the same as in Example 1.

[0159] Example 5

[0160] This example provides a negative electrode material, and the preparation method thereof is the same as in Example 1, except that:

[0161] The vacuum degree in step 3) is 50 Pa, and in step 4), the precursor material is collected on a water-cooled substrate at 900°C.

[0162] The production and evaluation of the secondary battery provided in this example are the same as in Example 1.

[0163] Example 6

[0164] This example provides a negative electrode material, and the preparation method thereof is the same as in Example 1, except that:

[0165] The pre-disproportionated silicon monoxide material in step 1) has a size of a block of 5 cm.

[0166] The production and evaluation of the secondary battery provided in this example are the same as in Example 1.

[0167] Comparative Example 1

[0168] This comparative example provides a negative electrode material, which is prepared in the same manner as in Example 2, except that:

[0169] In step 1), the silicon dioxide powder with a volume distribution D50 = 30 μm and the silicon powder with a volume distribution D50 = 10 μm are directly mixed in a molar ratio of 1:2 and placed in the first vacuum heating chamber of a vacuum heating system, argon is introduced, and heated to 1400°C; the temperature of the water-cooled substrate in the condensation deposition chamber in step 4) is 850°C; only methane and carrier gas nitrogen are introduced in step 6), and the proportion of the atmosphere is adjusted to 3:3.5.

[0170] The production and evaluation of the secondary battery provided in this example are the same as in Example 1.

[0171] The negative electrode materials prepared in Examples 1-6 and Comparative Example 1 are subjected to energy spectrum analysis of Mg elements, and the negative electrode material prepared in Example 3 is subjected to energy spectrum analysis of Ca elements, to obtain k1 and k2 values, respectively.

[0172] The specific test method for energy spectrum analysis: the prepared negative electrode material particles are cut open using a Hitachi E-3500 ion mill, the morphology and structure of the cross section are observed on a Hitachi S-4800 type cold field emission scanning electron microscope, and the element composition and distribution are observed using a British Oxford energy spectrometer.

[0173] The negative electrode materials prepared in Examples 1-6 and Comparative Example 1 are also subjected to pH value testing: 5.00±0.01 g of the powder sample is weighed and added to 45 mL of pure water, stirred and dispersed, and after ultrasonic treatment for 5 min, the upper clear liquid after standing is tested using a Mettler FE20 type pH meter to read the pH value.

[0174] True density test: the true density of the negative electrode material is tested by the gas adsorption expansion method using a U.S. Micromeritics true density instrument (AccuPyc II type).

[0175] Specific surface area test: the specific surface area of the material is calculated by the BET method using nitrogen adsorption using a U.S. Micromeritics specific surface area and pore analyzer (TriStar II type).

[0176] XRD test: the sample is characterized by XRD using an XRD diffractometer, the scanning range is 10°-90°, and the scanning step is 0.05°.

[0177] The performance test results of the negative electrode materials prepared in the above Examples 1-6 and Comparative Example 1 are shown in Table 1, and the electrochemical test results of the negative electrode materials prepared in the above Examples and Comparative Example in secondary batteries are shown in Table 2.

[0178] Table 1 Performance test results of the negative electrode materials prepared in the above Examples and Comparative Example

[0179]

[0180] Table 2 Electrochemical performance results of the batteries prepared in the above Examples and Comparative Example

[0181]

[0182] In addition, Figure 1 The XRD spectrum of the negative electrode material prepared in Example 1 is shown in which the MgSiO3(610) diffraction peak appears between 30°-31°, and the Si(220) diffraction peak appears between 45°-50°.

[0183] Figure 2 and Figure 3 The SEM / EDS surface scanning images of the Mg element in a certain particle section of the negative electrode material prepared in Example 1, and the high-magnification SEM image of the particle section are shown in Figs. 1 and 2, respectively. As can be seen from the figures, the metal silicate domain, the nano-silicon domain and the silicon oxide domain are uniformly and dispersedly distributed.

[0184] Figure 4 and Figure 5 The cycle-capacity graph and the cycle-expansion graph of the secondary batteries prepared in Example 1 and Comparative Example 1 are shown in Figs. 3 and 4, respectively. By comparison, it can be seen that the negative electrode material prepared in the present application has more excellent cycle performance and lower cycle expansion performance.

[0185] Finally, it should be noted that: the above examples are only used to illustrate the technical solutions of the present application, but not to limit them; although the present application has been described in detail with reference to the above examples, those skilled in the art should understand that: they can still modify the technical solutions recorded in the above examples, or make equivalent replacement for part or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the above examples.

[0186] Furthermore, to the extent that the terms "comprises", "comprising", "includes", "including" and "has" or any variation thereof are used in the specification and / or claims, these terms are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises, includes or has a list of elements does not include only those elements but can include other elements not expressly listed or inherent to such process, method, article, or apparatus. In addition, to the extent that the terms "coupled", "coupling", "connected", "connecting" or "connection" are used in the specification and / or claims, these terms are intended to refer to either a direct connection between entities that are in physical or logical contact with each other or an indirect connection through one or more intermediate entities.

Claims

1. A negative electrode material, characterized in that, It includes a silicon-based core and a carbon layer covering the surface of the silicon-based core, wherein the silicon-based core includes nano-silicon and silicates containing the metal element M; The negative electrode material is subjected to cross-sectional and energy dispersive spectroscopy (EDS) analysis. Surface scan analysis is performed on the cross-sections of n1 randomly selected particles to obtain n1 M element content values. The standard deviation k1 of the n1 M element content values ​​is calculated, where k1 ≤ 6.

91. Point scan analysis is performed on n2 randomly selected points within the cross-sections of the particles to obtain n2 M element content values. The standard deviation k2 of the n2 M element content values ​​is calculated, where k2 ≤ 3.7, and 0.1 < k2 / k1 ≤ 1, where n1 is a natural number greater than or equal to 5, and n2 is a natural number greater than or equal to 5.

2. The negative electrode material as described in claim 1, characterized in that, At least one of the following conditions must be met: (1) The silicon-based core also includes silicon oxide; (2) The pH value of the negative electrode material satisfies 7 < pH ≤ 10.5; (3) The M element includes at least one metallic element from Groups IA, IIA, and IIIA; (4) The M element includes at least one of lithium, sodium, potassium, magnesium, calcium, and aluminum; (5) The true density of the negative electrode material is 2.0 g / cm³. 3 -2.6g / cm 3 ; (6) The specific surface area of ​​the negative electrode material is 2m². 2 / g-10m 2 / g; (7) In the negative electrode material, the mass percentage of element M is 3%-20%, and the mass percentage of carbon layer is 1%-20%; (8) When the silicate containing metal element M includes MgSiO3, in the XRD spectrum of the negative electrode material, the diffraction peak of MgSiO3 (610) is between 30° and 31°, and the diffraction peak of Si (220) is between 45° and 50°, and the intensity ratio of the two diffraction peaks is α = I. Si(220) / I MgSiO 3 (610) , 0 < α < 2; (9) When the silicate containing metal element M includes MgSiO3, the average size of MgSiO3 grains on the (610) crystal plane is calculated to be ≤30nm based on the XRD spectrum of the negative electrode material and the Scherrer formula Kλ = 0.9λ / Bcosθ.

3. The negative electrode material as described in claim 2, characterized in that, It also meets at least one of the following conditions: (10) The nano-silicon is dispersed in the silicon oxide; (11) The silicate containing the metal M element is surrounded by the nano-silicon or the silicon oxide.

4. The negative electrode material according to any one of claims 1-3, characterized in that, The thickness of the carbon layer is 50nm-500nm.

5. A method for preparing a negative electrode material as described in any one of claims 1-4, characterized in that, include: The metal source material and the predisproportionated silicon suboxide material were placed at different positions in the same vacuum heating system and heated and evaporated separately to obtain metal source gas and silicon suboxide gas. The silicon suboxide gas and the metal source gas are mixed and condensed to obtain the core material; The core material is carbon-coated to obtain the anode material.

6. The preparation method according to claim 5, characterized in that, At least one of the following conditions must be met: A. The preparation method of the predisproportionated silicon suboxide material includes: predisproportionating amorphous SiO bulk to obtain silicon suboxide containing disproportionated silicon grains <10nm, and then pulverizing or crushing it to obtain the predisproportionated silicon suboxide powder or particles. B. The size of the predisproportionated silicon suboxide material is ≤10cm; C. The metal source material includes at least one of magnesium source material, lithium source material, sodium source material, potassium source material, calcium source material, and aluminum source material; D. The metal source gas includes at least one of magnesium vapor, lithium vapor, sodium vapor, potassium vapor, calcium vapor, and aluminum vapor; E. The heating and evaporation are carried out in a vacuum or inert gas atmosphere; F. The temperature at which the predisproportionated silicon suboxide material is heated and evaporated is 1000℃-1500℃; G. The temperature at which the metal source material is heated and evaporated is 600℃-1350℃; H. The condensation temperature is 500℃-800℃; I. The condensation method includes at least one of water cooling and air cooling; J. After condensation, the process further includes: collecting the condensed precursor material, crushing and classifying the precursor material to obtain the core material; K. The carbon coating treatment includes gas phase coating, liquid phase coating or solid phase coating.

7. The preparation method according to claim 6, characterized in that, At least one of the following conditions must be met: L. The pre-disproportionation treatment is carried out in an inert gas atmosphere, wherein the inert gas includes at least one of nitrogen, argon, and helium; M. The temperature of the pre-disproportionation treatment is 1000℃-1200℃; N. The heat preservation time for the pre-disproportionation treatment is 3h-10h; O. The magnesium source material includes at least one of the following: metallic magnesium powder, metallic magnesium ingots, metallic magnesium granules, a mixture of magnesium oxides and reducing substances, and a mixture of magnesium salts and reducing substances; P. The pulverization method includes mechanical pulverization, ball milling, or air jet milling; Q. The gas encapsulated in the gas phase includes a carbon source gas and a carrier gas; R. The temperature of the gas phase coating is 700℃-1000℃.

8. The preparation method according to claim 7, characterized in that, At least one of the following conditions must be met: S. The carbon source gas includes at least one of methane, ethane, propane, butane, ethylene, propylene, and acetylene; T. The carrier gas includes at least one of nitrogen, argon, and helium; U. The gas encapsulated in the gas phase also includes hydrogen.

9. The preparation method according to any one of claims 5-8, characterized in that, The silicon suboxide gas and the metal source gas are mixed under vacuum conditions of 0-100 Pa.

10. A secondary battery, characterized in that, Includes the negative electrode material as described in any one of claims 1-4.

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